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- Title
- Debonding fracture of foam core sandwich structure.
- Creator
- Li, Xiaoming., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A new test specimen, named tilted sandwich debond specimen (TSD), has been Introduced to promote face/core debonding over crack kinking and enable characterization of an important failure mode of sandwich structures. An experimental compliance calibration procedure was developed for evaluation of debond fracture toughness in a straight-forward manner. The specimen has been evaluated through kinematics analysis, elastic foundation model, finite element analysis and a comprehensive experimental...
Show moreA new test specimen, named tilted sandwich debond specimen (TSD), has been Introduced to promote face/core debonding over crack kinking and enable characterization of an important failure mode of sandwich structures. An experimental compliance calibration procedure was developed for evaluation of debond fracture toughness in a straight-forward manner. The specimen has been evaluated through kinematics analysis, elastic foundation model, finite element analysis and a comprehensive experimental investigation. An elastic foundation model of the TSD specimen was developed to obtain analytical expressions for specimen compliance and strain energy release rate. A design equation for the maximum tolerable crack length was derived. Finite element analysis of various configurations of the TSD specimen was conducted to obtain the mixed mode stress intensity factors, crack kinking angle, specimen compliance and strain energy release rate. The results revealed that the bimaterial character of the TSD specimen influences the mode mixity for the specimen and that crack kinking was more likely for thick and low density cores. The presence of the interphase layer only slightly influenced the mode mixity and kinking angle. The debonding characteristics of several sandwiches consisting of glass/vinylester face sheets and PVC foam cores of various densities were examined using the TSD specimen. Crack propagation from the beelcore precrack involved "micro-kinking" or kinking deeply in the core for all specimens at the first crack propagation increment(s). Crack kinking in the intermediate density core could be suppressed by selecting a certain range of tilt angles. After kinking, crack returned to a path parallel and close to the interface in agreement with the analysis of sub-interface cracks. Cracks propagated in a stick/slip manner. Measurements of the debond fracture toughness, Gc, using the TSD specimen revealed that Gc is fairly independent of crack length and increases with increasing core density. The debond toughness was of similar order as the mode I toughness of the core.
Show less - Date Issued
- 2000
- PURL
- http://purl.flvc.org/fcla/dt/12625
- Subject Headings
- Sandwich construction, Fracture mechanics
- Format
- Document (PDF)
- Title
- Factors influencing face/core crack propagation in PVC foam core sandwich.
- Creator
- Viana, Gillmer Manuel., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Fracture toughness of a large range of PVC foam cores was determined using the single edge notch bend (SENB) specimen. Debond fracture toughness for sandwich specimens with the same foam cores was characterized using the TSD specimen. Examination of the crack propagation path in specimens with adequate face/core adhesion revealed that the debonding process occurred by crack propagation in the core, near the face/core interface. It was observed that the debond toughness and core toughness are...
Show moreFracture toughness of a large range of PVC foam cores was determined using the single edge notch bend (SENB) specimen. Debond fracture toughness for sandwich specimens with the same foam cores was characterized using the TSD specimen. Examination of the crack propagation path in specimens with adequate face/core adhesion revealed that the debonding process occurred by crack propagation in the core, near the face/core interface. It was observed that the debond toughness and core toughness are of similar magnitude although the debond toughness exceeds the core toughness, especially for the higher density cores. Possible reasons for the elevation of the debond toughness over the core toughness such as plastic zone enlargement, mode mixity, core thickness, and gradient of properties of the core are examined. It was found that the plastic zone enlargement is a major factor for increase in debond toughness over the other factors examined.
Show less - Date Issued
- 2001
- PURL
- http://purl.flvc.org/fcla/dt/12751
- Subject Headings
- Sandwich construction, Fracture mechanics
- Format
- Document (PDF)
- Title
- FRACTURE MECHANICS OF FIBER REINFORCED CONCRETE AND THE DURABILITY OF FIBER REINFORCED AND AIR-ENTRAINED CONCRETE EXPOSED TO FREEZE-THAW CYCLES (FATIGUE).
- Creator
- JEANFREAU, JAMES JOSEPH, JR., Florida Atlantic University, Arockiasamy, Madasamy
- Abstract/Description
-
This thesis presents the experimental and analytical investigation of fiber (steel and Kevlar) reinforced concrete (FRC) to determine its fracture mechanic properties especially the J-integral. The freeze-thaw durability of fiber reinforced and air-entrained concrete is also investigated. The fiber reinforced concretes were found to have a much greater flexural strength and toughness compared to plain concrete. The compressive strength was found to decrease with the addition of fibers and air...
Show moreThis thesis presents the experimental and analytical investigation of fiber (steel and Kevlar) reinforced concrete (FRC) to determine its fracture mechanic properties especially the J-integral. The freeze-thaw durability of fiber reinforced and air-entrained concrete is also investigated. The fiber reinforced concretes were found to have a much greater flexural strength and toughness compared to plain concrete. The compressive strength was found to decrease with the addition of fibers and air-entrainment. In all cases the addition of 1.0% or more fibers prevented catastrophic failures. The mixing and setting of FRC requires a rigorous procedure which must be followed to achieve a homogeneous matrix.
Show less - Date Issued
- 1986
- PURL
- http://purl.flvc.org/fcla/dt/14334
- Subject Headings
- Reinforced concrete, Fiber, Fracture mechanics
- Format
- Document (PDF)
- Title
- Deformation and fatigue crack growth of iron(81) boron(13.5) silicon(3.5) carbon(2) amorphous metal using magnetostrictive behavior to generate delta K.
- Creator
- Willard, Alan Eugene., Florida Atlantic University, Salivar, Gary C., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The deformation and fatigue crack growth behavior of amorphous metals are presented. A discussion of magnetic domains, and their influence on magnetostriction is also included. Testing of Metglas 2605SC, utilizing magnetostriction to generate DeltaK, indicated near-threshold (Region I) fatigue crack growth behavior for as-cast and annealed specimens. A Delta Kth on the order of 0.6-1.0 kg/mm^3/2 was also indicated. The best crack growth rate behavior was obtained for transverse field-annealed...
Show moreThe deformation and fatigue crack growth behavior of amorphous metals are presented. A discussion of magnetic domains, and their influence on magnetostriction is also included. Testing of Metglas 2605SC, utilizing magnetostriction to generate DeltaK, indicated near-threshold (Region I) fatigue crack growth behavior for as-cast and annealed specimens. A Delta Kth on the order of 0.6-1.0 kg/mm^3/2 was also indicated. The best crack growth rate behavior was obtained for transverse field-annealed specimens. Significant variability in the data, however, prevented a determination of Delta Kth for this condition. A life prediction model based on a Paris equation was developed. Crack growth data were consistently lower than predicted by the Region II model, which would be expected for near-threshold data. Fractographic analyses supported the influence of domains on crack growth behavior. The scatter in the Region I data appears to be contributed by the effects of domains and domain walls.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14736
- Subject Headings
- Fracture mechanics, Metals--Fatigue, Magnetostriction
- Format
- Document (PDF)
- Title
- Weight function approach for stress analysis of the surface crack in a finite plate subjected to nonuniform stress fields.
- Creator
- Jani, Jayant Shivkumar., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The effects of various nonuniform stress fields on the stress intensity factors for the semi-elliptic surface crack (three-dimensional problem) in a finite plate are determined using the weight function approach. The formulation satisfies the linear elastic fracture mechanics criteria and the principle of conservation of energy. Based on the knowledge of stress intensity solutions for the reference load/stress system, the expression for the crack opening displacement function for the surface...
Show moreThe effects of various nonuniform stress fields on the stress intensity factors for the semi-elliptic surface crack (three-dimensional problem) in a finite plate are determined using the weight function approach. The formulation satisfies the linear elastic fracture mechanics criteria and the principle of conservation of energy. Based on the knowledge of stress intensity solutions for the reference load/stress system, the expression for the crack opening displacement function for the surface crack is derived. Using the crack opening displacement function and the reference stress intensity factor, the three-dimensional weight functions and subsequently the stress intensity solutions for the surface crack subjected to nonuniform stress fields are derived. The formulation is then applied to determine the effects of linear, quadratic, cubic, and pure bending stress fields on the stress intensity factor for the surface crack in a finite plate. In the initial stage of the study a two-dimensional problem of an edge-crack emanating from the weld-toe in a T-joint is considered. The effect of parameters such as plate thickness, weld-toe radius, and weld-flank angle on the stress intensity factor for an edge-crack is studied. Finite element analyses of the welded T-joints are performed to study the effects of plate thickness, weld-toe radius and the weld-flank angle on the local stress distribution. The ratio of plate thickness to weld-toe radius ranging from 13.09 to 153.93, and the weld-flank angles of 30, 45, and 60 degrees are considered in the analyses. Based on the results from FEM analyses, a parametric equation for the local stress concentration factor and a polynomial expression for the local stress distribution across the plate thickness are derived using the method of least squares and the polynomial curve-fitting technique.
Show less - Date Issued
- 1990
- PURL
- http://purl.flvc.org/fcla/dt/12254
- Subject Headings
- Strains and stresses, Plates (Engineering), Fracture mechanics
- Format
- Document (PDF)
- Title
- A combined FEM-fracture mechanics analysis approach for I.C. packages.
- Creator
- Renavikar, Ajit Anand., Florida Atlantic University, Stevens, Karl K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A study of the stress distribution in and fracture behavior of the hermetic glass seal in a typical Integrated Circuit package is presented herein. Finite Element Analysis and Fracture Mechanics approaches were found effective for this investigation. A prescribed load or displacement applied at the tip of the lead protruding from the package causes high stresses at the lead-glass interface, which can lead to cracking and fracture of the seal. An approach for finding the value of the allowable...
Show moreA study of the stress distribution in and fracture behavior of the hermetic glass seal in a typical Integrated Circuit package is presented herein. Finite Element Analysis and Fracture Mechanics approaches were found effective for this investigation. A prescribed load or displacement applied at the tip of the lead protruding from the package causes high stresses at the lead-glass interface, which can lead to cracking and fracture of the seal. An approach for finding the value of the allowable load or displacement applicable at the lead tip is discussed. A correlation with a standard crack shape is presented for the 3-D model of the package. An extension of the problem revealing the effects of crack propagation on the stress intensity factor for the glass material is presented in later chapters. The J-integral method from Fracture Mechanics is found to be extremely useful for this investigation. A decline in the stress intensity factor with crack growth was observed from this study.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14511
- Subject Headings
- Integrated circuits--Fracture, Fracture mechanics, Finite element method, Electronics--Materials--Fatigue
- Format
- Document (PDF)
- Title
- FACE/CORE DISBONDING FRACTURE OF HONEYCOMB CORE SANDWICH PANELS.
- Creator
- Tauhiduzzaman, Mohammad, Carlsson, Leif A., Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
The objective of the research presented in this thesis is to develop analysis and test procedures for the characterization of disbonding crack growth in a honeycomb (HC) core sandwich structure. Face sheet-to-core disbonding are of particular interest to aircraft certification authorities due to several in-service occurrences. Experimental investigation was initially focused on the mode I dominated Single Cantilever Beam (SCB) test method. Various data reduction methodologies were employed to...
Show moreThe objective of the research presented in this thesis is to develop analysis and test procedures for the characterization of disbonding crack growth in a honeycomb (HC) core sandwich structure. Face sheet-to-core disbonding are of particular interest to aircraft certification authorities due to several in-service occurrences. Experimental investigation was initially focused on the mode I dominated Single Cantilever Beam (SCB) test method. Various data reduction methodologies were employed to determine the fracture toughness. The MBT method produced the most consistent and conservative results. Finite element analysis (FEA) a double periodic array of hexagonal cells was conducted to determine the effective in-plane extensional modulus and Poisson ratio of the HC core. It was shown that deformation constraints on the core, due to attachment of the core to rigid face sheets, will drastically change the behavior of the HC core. The response changes from being governed by bending to stretching which substantially elevates the effective in-plane modulus. Fracture mechanics analysis of a face/core interface crack in a HC core SCB specimen was performed using FEA. The influence of in-plane properties of the constrained core on energy release rate and mode mixity phase angle was examined. Use of plane strain conditions and an elevated modulus of the constrained core in the analysis is recommended. The approach is substantiated by testing of HC core SCB sandwich. Test results showed good agreement with FEA prediction of compliance and kink angle.
Show less - Date Issued
- 2019
- PURL
- http://purl.flvc.org/fau/fd/FA00013419
- Subject Headings
- Honeycomb structures, Fracture mechanics, Strength of materials, Airframes--Materials
- Format
- Document (PDF)
- Title
- Stress distribution around a transverse circular opening through the midspan of a double reinforced beam.
- Creator
- Anesta, Heather R., College of Engineering and Computer Science, Department of Civil, Environmental and Geomatics Engineering
- Abstract/Description
-
This manuscript predicts the behavior of a doubly reinforced concrete beam with a circular opening at its midspan by closely analyzing traditional beam theory and design. It then confirms these predictions with finite element modeling software while providing design suggestions. The analysis is limited to the tensile and compressive stresses and cracking behavior. The objectives are to determine the stress distribution around a circular opening that agrees with conventional beam theory. The...
Show moreThis manuscript predicts the behavior of a doubly reinforced concrete beam with a circular opening at its midspan by closely analyzing traditional beam theory and design. It then confirms these predictions with finite element modeling software while providing design suggestions. The analysis is limited to the tensile and compressive stresses and cracking behavior. The objectives are to determine the stress distribution around a circular opening that agrees with conventional beam theory. The beam behavior is examined from zero load to failure load. ANSYS is utilized in lieu of real world testing, and the appendix includes the finite element results for a beam including design recommendations. The results lay the foundation for a possible new design procedure of concrete beams with single or multiple circular openings. This research offers useful information that was unavailable previously. More research can be conducted to help designers to design lighter, more efficient concrete beams.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2867327
- Subject Headings
- Reinforced concrete construction, Structural design, Strains and stresses, Fracture mechanics
- Format
- Document (PDF)
- Title
- Durability and fracture toughness of fly ash concrete in the marine environment.
- Creator
- Lee, Seung-Kyoung, Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This thesis presents the experimental investigation of durability and fracture toughness (K IC) of fly ash concrete in the marine environment. The findings indicate that the deterioration rate of durability parameters, such as compressive strength, weight loss, and dynamic modulus of elasticity, due to 450 wet and dry cycles exposure (the Accelerated Durability Testing), was inversely proportional to the amount of fly ash replacement. On the other hand, tensile strength properties, such as...
Show moreThis thesis presents the experimental investigation of durability and fracture toughness (K IC) of fly ash concrete in the marine environment. The findings indicate that the deterioration rate of durability parameters, such as compressive strength, weight loss, and dynamic modulus of elasticity, due to 450 wet and dry cycles exposure (the Accelerated Durability Testing), was inversely proportional to the amount of fly ash replacement. On the other hand, tensile strength properties, such as modulus of rupture and fracture toughness, were independent of fly ash replacement, but increased with the period of accelerated testing. The mean K IC values of fly ash concrete mixes showed that they are closely related to their compressive strengths and size effects. According to AE, unstable crack propagation initiated at 93-97% maximum load. With SEM observations, it was found that crystallized particles were precipitated in the void spaces due to chemical reaction between the cement paste and seawater.
Show less - Date Issued
- 1990
- PURL
- http://purl.flvc.org/fcla/dt/14614
- Subject Headings
- Fly ash, Concrete--Cracking, Fracture mechanics, Concrete--Testing
- Format
- Document (PDF)
- Title
- Mode II interlaminar fracture toughness of interleaved composite materials.
- Creator
- Aksoy, Adnan., Florida Atlantic University, Carlsson, Leif A.
- Abstract/Description
-
Interlaminar mode II fracture toughness, GIIC, of thermoset and thermoplastic interleaved (TSI and TPI) composites were investigated over a wide range of interleaf thickness. TPI specimens had four to about seven times larger GIIC than those without an interleaf. Poor adhesion observed for some TPI specimens were likely to be due to contaminated film materials. Thermoset interleaves were less effective in enhancing the mode II fracture toughness. However, even 0.043 mm thermoset interleaves...
Show moreInterlaminar mode II fracture toughness, GIIC, of thermoset and thermoplastic interleaved (TSI and TPI) composites were investigated over a wide range of interleaf thickness. TPI specimens had four to about seven times larger GIIC than those without an interleaf. Poor adhesion observed for some TPI specimens were likely to be due to contaminated film materials. Thermoset interleaves were less effective in enhancing the mode II fracture toughness. However, even 0.043 mm thermoset interleaves gave three times larger G$\sb{\rm IIC}$ than those without an interleaf. Estimates of the volume of the yielded material around the crack tip based on a quasi-elastic finite element approach and Irwin's model showed that the yield zone height reaches a peak value for increasing interleaf thickness for both TSI and TPI specimens. Furthermore, fracture toughness data correlates well with yield zone heights.
Show less - Date Issued
- 1990
- PURL
- http://purl.flvc.org/fcla/dt/14594
- Subject Headings
- Composite materials--Cracking, Fracture mechanics, Composite materials--Testing
- Format
- Document (PDF)
- Title
- Mode I interlaminar fracture toughness of interleaved graphite/epoxy.
- Creator
- Ozdil, Feridun., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Mode I interlaminar fracture toughness, G IC, of interleaved graphite/epoxy has been investigated with DCB specimens, beam theory, and finite element analysis. Finite element modeling aimed to investigate the influence of interleaf thickness on compliance and energy release rate and possible mixed mode loading in the case of asymmetric interfacial crack. Another objective was to compute crack tip yield zone dimensions as a function of thickness and elastic properties of the interleaf material...
Show moreMode I interlaminar fracture toughness, G IC, of interleaved graphite/epoxy has been investigated with DCB specimens, beam theory, and finite element analysis. Finite element modeling aimed to investigate the influence of interleaf thickness on compliance and energy release rate and possible mixed mode loading in the case of asymmetric interfacial crack. Another objective was to compute crack tip yield zone dimensions as a function of thickness and elastic properties of the interleaf material. The analysis is correlated with experiments. Thermoplastic interleaves enhanced G IC to a great extent. The toughness increased sharply with film thickness to a maximum at 16 mu m and decreased for the thicker interleaves. On the other hand, inadequate adhesion preempted the toughness potential of thermoset interleaves.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14682
- Subject Headings
- Laminated materials--Testing, Fracture mechanics, Strength of materials
- Format
- Document (PDF)
- Title
- Investigation of debonding and crack kinking in foam core sandwich beams.
- Creator
- Prasad, Srinivas., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Debond failures in structural sandwich may lead to severe reductions in load-bearing capability of the structure because of impartial transfer of shear and tensile forces between facing and core due to the lack of interfacial bonding. Analysis of interfacial bonding in sandwich specimens subjected to transverse tensile and shear forces is presented. Stress intensity factors computed based on the near-tip displacement field are related to experimental crack growth observation on the sandwich...
Show moreDebond failures in structural sandwich may lead to severe reductions in load-bearing capability of the structure because of impartial transfer of shear and tensile forces between facing and core due to the lack of interfacial bonding. Analysis of interfacial bonding in sandwich specimens subjected to transverse tensile and shear forces is presented. Stress intensity factors computed based on the near-tip displacement field are related to experimental crack growth observation on the sandwich beams with aluminum skins on a wide range of PVC foam cores. Experimentally it was found that the crack tends to grow at the interface between the bondline and core as opposed to skin/bondline interface. In shear dominated fields, a pre-existing flow tended to deflect into the core rather than grow along the interface. The tendency for kinking and the direction of the kink is examined experimentally and analyzed using the finite element method.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14861
- Subject Headings
- Finite element method, Sandwich construction, Diffusion bonding (Metals), Fracture mechanics
- Format
- Document (PDF)
- Title
- Nanoparticle Reinforced Core Materials for Sandwich Construction: Investigation of Mechanical and Fracture Behavior.
- Creator
- Stewart, Justin Keith, Mahfuz, Hassan, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Sandwich composites provide excellent structural integrity for a variety of applications. In this study pristine and functionalized 30 nrn Silicon Carbide nanoparticles are infused into a low density polyurethane foam used for the inner core of the sandwich structure. The mechanical properties are characterized using compressive, tensile, and flexural tests. A plane-strain fracture test and a TSD (Tilted Sandwich Debond) test characterize the fracture properties of the foam and the coreskin...
Show moreSandwich composites provide excellent structural integrity for a variety of applications. In this study pristine and functionalized 30 nrn Silicon Carbide nanoparticles are infused into a low density polyurethane foam used for the inner core of the sandwich structure. The mechanical properties are characterized using compressive, tensile, and flexural tests. A plane-strain fracture test and a TSD (Tilted Sandwich Debond) test characterize the fracture properties of the foam and the coreskin interface. Thermal characterization is carried out using Dynamic Mechanical Analysis (DMA) and Thermo-Gravimetric Analysis (TGA). FTIR spectral analysis reveals changes in molecular bonding due to pristine and functionalized nanoparticle infusion. The fracture resistance of the foam is improved and the delamination strength of the sandwich construction with nanophased cores is dramatically improved. The TSD testing indicated that the G1c value rose from 0.14 kJ/m^2 in the neat foam to 0.56 kJ/m^2 with just 0.1 wt% of SiC nanoparticle inclusion reflecting an enhancement of almost 300%.
Show less - Date Issued
- 2008
- PURL
- http://purl.flvc.org/fau/fd/FA00012558
- Subject Headings
- Composite materials--Mechanical properties, Nanostructured materials--Testing, Fracture mechanics
- Format
- Document (PDF)
- Title
- Local buckling and debond propagation in sandwich columns and panels.
- Creator
- Aviles, Francis., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The local buckling failure mechanism and subsequent debond propagation in sandwich columns and panels with composite face sheets containing a face-to-core debond is experimentally, analytically, and numerically analyzed. The experimental investigation is based on a comprehensive test program to examine local buckling failure and fracture toughness of sandwich specimens consisting of glass/epoxy face sheets over various density PVC foams and a balsa wood core. Elastic foundation and finite...
Show moreThe local buckling failure mechanism and subsequent debond propagation in sandwich columns and panels with composite face sheets containing a face-to-core debond is experimentally, analytically, and numerically analyzed. The experimental investigation is based on a comprehensive test program to examine local buckling failure and fracture toughness of sandwich specimens consisting of glass/epoxy face sheets over various density PVC foams and a balsa wood core. Elastic foundation and finite element models are developed for prediction of the local buckling load of sandwich columns and panels containing an implanted debond at the face/core interface. Nonlinear finite element analysis was conducted to investigate debond propagation in the post-buckling region. Overall, model predictions were in agreement with experimental results. The buckling load was found to decrease with reduced face sheet stiffness, reduced core modulus, and increased debond length. Sandwich panels with circular debonds were more resistant to local buckling than those with square debonds of the same characteristic size. Circular debonds of 50 mm diameter and square debonds of 45 mm side length established the threshold for local buckling failure. Nonlinear finite element analysis of debonded sandwich columns and panels showed that the major crack displacement is opening (mode I). The tendency of the crack tip to first open and then close after buckling of the face sheet is believed to be due to the formation of an eccentric load path at the onset of buckling. The fracture mechanics analysis of debonded sandwich panels showed that the energy release rate is much higher in the direction perpendicular to the applied load than along the loading direction, and exceeds the measured toughness value in the transverse direction. This explains the experimental observation that a debond embedded in a sandwich panel tends to propagate in the transverse direction.
Show less - Date Issued
- 2005
- PURL
- http://purl.flvc.org/fau/fd/FADT12123
- Subject Headings
- Buckling (Mechanics), Sandwich construction, Fracture mechanics, Diffusion bonding (Metals), Strength of materials
- Format
- Document (PDF)
- Title
- Development and implementation of an adaptive controller for station keeping of small outboard-powered vessels.
- Creator
- Fisher, Aaron D., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In this thesis multiple controllers are developed which command a small boat with twin tied outboard motors to hold a desired position. In the process of developing a controller to hold a position, controllers were first developed which follow a desired heading or path over ground with the motors outputting constant thrust. These heading and path following controllers were tuned and tested in a numerical simulation, then validated on the R/V Lee and Ocean Power vessels through sea trials in...
Show moreIn this thesis multiple controllers are developed which command a small boat with twin tied outboard motors to hold a desired position. In the process of developing a controller to hold a position, controllers were first developed which follow a desired heading or path over ground with the motors outputting constant thrust. These heading and path following controllers were tuned and tested in a numerical simulation, then validated on the R/V Lee and Ocean Power vessels through sea trials in the Atlantic Ocean. After successful path following trials were performed, station keeping algorithms were developed and tuned in the numerical simulation, now with heading and thrust of the vessel both being variables to be controlled. After tuning in the numerical simulation, the Ocean power vessel was outfitted with systems for controlling throttle and steering with sea trials conducted in the Atlantic Ocean for station keeping.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2975247
- Subject Headings
- Ship handling, Stability of ships, Fracture mechanics, Boats and boating, Design, PID controllers, Computer simulation
- Format
- Document (PDF)
- Title
- Use of hybrid Rice Husk Ash-Fly Ash mixtures as sustainable supplementary materials for concrete in the marine environment.
- Creator
- Arboleda, Diana., College of Engineering and Computer Science, Department of Civil, Environmental and Geomatics Engineering
- Abstract/Description
-
This paper presents the comparison of shrinkage and corrosion characteristics of optimized hybrid Rice Husk Ash (RHA)/Fly Ash (FA)-modified Concrete, with those of normal concrete in the marine environment. Uses of both FA and RHA have numerous environmental benefits. Shrinkage performance was determined by subjecting the mixes to restrained shrinkage testing per ASTM C1581. The time to cracking of the specimens improved an average of 18% with the hybrid mixes. Corrosion testing of reinforced...
Show moreThis paper presents the comparison of shrinkage and corrosion characteristics of optimized hybrid Rice Husk Ash (RHA)/Fly Ash (FA)-modified Concrete, with those of normal concrete in the marine environment. Uses of both FA and RHA have numerous environmental benefits. Shrinkage performance was determined by subjecting the mixes to restrained shrinkage testing per ASTM C1581. The time to cracking of the specimens improved an average of 18% with the hybrid mixes. Corrosion testing of reinforced columns was performed in a simulated tidal cycle Marine Environment. Corrosion potential improved by as much as 35% for the mix with the highest FA/RHA replacement, and corrosion activity as measured with potentiostat equipment improved by an average of 34% . These results indicate a clear performance improvement of the modified concrete that is proportional to the percent replacement of cement.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2138109
- Subject Headings
- Fracture mechanics, Concrete, Additives, Testing, Fly ash, Testing, Concrete, Cracking, Prevention, Industrial minerals, Testing
- Format
- Document (PDF)
- Title
- Interlaminar mode III fracture ECT method - testing and analysis.
- Creator
- Browning, Grant., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack...
Show moreIn an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack front are determined to examine the uniformity of mode III loading and mode II influence. The shear stress distributions in the one-point and two-point tests are virtually identical, indicating that either of the two tests could be used interchangeably. Based on the uniformity of the mode III shear stress distribution along the crack front, it was found that the ECT specimen should have minimum overhang. Longer crack lengths tend to produce nonuniform shear stress distributions. A modified two-point ECT test fixture was developed to allow testing of specimens with a range of dimensions. This development enabled experimental verification of the results from the FEA overhang series. The specimens with a minimum overhang produced consistant mode III toughness data. The most reliable way to reduce data is through the original compliance calibration method. A modified ECT specimen was developed with a staggered crack front to produce uniform mode III crack growth. Finite element analysis of the modified ECT specimen shows a uniform mode III stress distribution along the crack front with little mode II interaction.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/187206
- Subject Headings
- Laminated materials, Testing, Fracture mechanics, Strength of materials, Testing, Composite materials, Testing
- Format
- Document (PDF)
- Title
- Automatic Station Keeping of Small Twin Screw Boats.
- Creator
- VanZwieten, James H., Driscoll, Frederick R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This work details the development of tools and controllers for station keeping control of twin screw vessels. A fundamental analysis is conducted of the dynamics of twin screw displacement hull vessels and their actuator systems, where the response characteristics and maneuverability are quantified through a series of full scale trials conducted in different environmental conditions while recording the environmental conditions, actuator states, and geodetic and inertial measurements. The data...
Show moreThis work details the development of tools and controllers for station keeping control of twin screw vessels. A fundamental analysis is conducted of the dynamics of twin screw displacement hull vessels and their actuator systems, where the response characteristics and maneuverability are quantified through a series of full scale trials conducted in different environmental conditions while recording the environmental conditions, actuator states, and geodetic and inertial measurements. The data from these maneuvers were repeatable from run to run and thus provide valuable benchmarks for several maneuvers and the measured actuator response provides valuable set points of performance characteristics/limitations for control development. A comprehensive general simulation of small twin screw displacement hull boats is developed as a tool to estimate ship and actuator responses in support of developing and tuning of control systems. The model and computer simulation is capable of modeling a wide range of the surface vessels, including their actuators and environmental conditions. This model proved to be accurate, when compared to the sea trial data, and model estimates have rms velocity errors for the various steady maneuvers of 1.2-4.6% for surge, 12.6-17.9% for sway, and 7.6-20.2% for yaw. A path following station keeping controller is developed that uses Lyapunov stability analysis to determine the path the vessel should follow to effectively eliminate position error. This controller showed good performance for several different environmental conditions. Encouraged by these finding, three additional station keeping control methodologies are developed for twin screw surface ships. All four of these controllers are examined for their robustness to environmental conditions, as well as their sensitivity to sensor precision, sensor update rates, and actuator limitations. All controllers are evaluated in sea state 4 yielding rms position errors from 3.3 to 16.2 m, the rms surge and sway accelerations are under 0.62 m/s , and the engine shifting frequencies are between 0.011 and 0.145 Hz. These four controllers are then tested over a wide range of environmental conditions, sensor precisions and update rates, and actuator response rates. The results from these tests give quantitative data that will aid in selecting the appropriate controller for a specific application, and will assist in selecting appropriate sensors.
Show less - Date Issued
- 2007
- PURL
- http://purl.flvc.org/fau/fd/FA00012579
- Subject Headings
- Boats and boating--Design, Actuators--Testing, Fracture mechanics, Lyapunov functions
- Format
- Document (PDF)
- Title
- Peel-off characteristics of carbon fiber laminates bonded to concrete.
- Creator
- Barbosa, Mauro., Florida Atlantic University, Arockiasamy, Madasamy
- Abstract/Description
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This study presents the experimental and theoretical studies on debond of carbon fiber laminates bonded to concrete, which aids in understanding the mechanics of the repaired damaged prestressed concrete girders with externally bonded carbon plates. The bond strength of carbon plate specimens bonded to concrete is determined experimentally by the debond test. The initial crack is introduced in the specimens at one location, namely the plate/adhesive interface. The fracture toughness for...
Show moreThis study presents the experimental and theoretical studies on debond of carbon fiber laminates bonded to concrete, which aids in understanding the mechanics of the repaired damaged prestressed concrete girders with externally bonded carbon plates. The bond strength of carbon plate specimens bonded to concrete is determined experimentally by the debond test. The initial crack is introduced in the specimens at one location, namely the plate/adhesive interface. The fracture toughness for debonding is evaluated and expressed as the critical strain energy release rate. A finite element analysis was performed to evaluate the compliance and stress distribution in the debond test specimens.
Show less - Date Issued
- 2000
- PURL
- http://purl.flvc.org/fcla/dt/12669
- Subject Headings
- Prestressed concrete construction--Maintenance and repair, Fracture mechanics, Carbon composites
- Format
- Document (PDF)
- Title
- Stress intensity factors and weight functions for surface cracks using boundary/finite element alternating methods.
- Creator
- Mu, Ruijia., Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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In the present investigation, the boundary/finite element alternating methods are used to evaluate the stress intensity factors and weight functions for surface crack problems. For two dimensional problems, Westergaard stress functions are used to find the analytical solutions for an infinite plate with an embedded crack, subjected to crack face tractions, and the boundary element method for the numerical solution. The stress intensity factors and weight functions for an arbitrary plate with...
Show moreIn the present investigation, the boundary/finite element alternating methods are used to evaluate the stress intensity factors and weight functions for surface crack problems. For two dimensional problems, Westergaard stress functions are used to find the analytical solutions for an infinite plate with an embedded crack, subjected to crack face tractions, and the boundary element method for the numerical solution. The stress intensity factors and weight functions for an arbitrary plate with an edge crack subjected to mixed mode loads are obtained by the alternating technique. For three dimensional problems, an elliptical coordinate system and the gravity potential functions are used to derive the three dimensional analytical solutions for an infinite solid with an embedded crack. The analytical solutions are derived for the cases of shear tractions and normal tractions, separately, by assuming that the tractions are symmetric about both the major and minor axes. Superposition gives the general solutions. The analytical solutions and the finite element method, in conjunction with alternating technique, are used to evaluate the stress intensity factors for a solid with a semi-elliptical surface crack, subjected to arbitrary loads. A general approach to evaluate the weight functions for a two dimensional plate with a three dimensional semi-elliptical surface crack is formulated. Numerical examples are evaluated using the formulation developed in the present investigation. The results show good agreement with those from classical solutions. The convergence characteristics of the alternating methods are also discussed. Finally, the formulation is applied to welded plate T-joints with edge/semi-elliptical surface cracks, subjected to three point bending, to obtain stress intensity factors.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/12319
- Subject Headings
- Fracture mechanics, Finite element method--Data processing, Materials--Fatigue, Strains and stresses
- Format
- Document (PDF)
