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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
- Flexural failure of curved sandwich beams with implanted interfacial debonds.
- Creator
- Layne, Andrew Maxwell., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Effects of face/core debonding on the structural integrity of curved sandwich beams subjected to opening bending moments has been examined experimentally. Curved beams of glass/polyester faces and PVC H30 foam core were manufactured. Various sizes of debonds were created using thin Teflon sheets inserted at the outer face/core interface during processing. A fixture for testing curved beams in flexure was designed, manufactured and evaluated. Surface strains at the middle of the curve were...
Show moreEffects of face/core debonding on the structural integrity of curved sandwich beams subjected to opening bending moments has been examined experimentally. Curved beams of glass/polyester faces and PVC H30 foam core were manufactured. Various sizes of debonds were created using thin Teflon sheets inserted at the outer face/core interface during processing. A fixture for testing curved beams in flexure was designed, manufactured and evaluated. Surface strains at the middle of the curve were recorded. Buckling of the debonded face sheet occurred followed by face/core propagation of the debond. Strength reduction of the beams under opening moments due to face/core debonding was substantial.
Show less - Date Issued
- 2000
- PURL
- http://purl.flvc.org/fcla/dt/12688
- Subject Headings
- Sandwich construction, Flexure
- Format
- Document (PDF)
- Title
- Compression failure of sandwich specimens with and without face/core debonds.
- Creator
- Vadakkeveedu, Vinod P., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The objective of this thesis is to report on an experimental study on the compressive behavior of foam cored sandwich composite specimens with and without face/core debond. A test fixture was designed which enables a precisely machined sandwich specimen instrumented with back-to-back strain gages to be loaded in edgewise compression. Tests were conducted on specimens without implanted face/core interface debonds over a range of core densities and gage lengths. The experimentally determined...
Show moreThe objective of this thesis is to report on an experimental study on the compressive behavior of foam cored sandwich composite specimens with and without face/core debond. A test fixture was designed which enables a precisely machined sandwich specimen instrumented with back-to-back strain gages to be loaded in edgewise compression. Tests were conducted on specimens without implanted face/core interface debonds over a range of core densities and gage lengths. The experimentally determined compression strengths and failure modes were compared to closed-form predictions and finite element analysis. Specimens with an implanted through-the-width face/core debond were also tested and mechanism of failure was analyzed using finite element analysis. Good agreement between collapse loads predicted using geometrically nonlinear analysis and experimentally measured strengths was observed.
Show less - Date Issued
- 2003
- PURL
- http://purl.flvc.org/fcla/dt/13047
- Subject Headings
- Sandwich construction, Strains and stresses, Structural analysis (Engineering)
- 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
- INFLUENCE OF DEFORMATION CONSTRAINTS OF HONEYCOMB CORE CELLS ON THE BENDING STIFFNESS OF SINGLE-FACE SANDWICH.
- Creator
- Ayanoglu, Mustafa Oguzhan, Carlsson, Leif A., Du, E, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
This research focuses on deformation constraints of honeycomb core cells in a sandwich imposed by bonds to the face sheets. Specifically, the influence of one-sided core constraints on the bending stiffness of a single-face honeycomb core sandwich is examined. To characterize the unconstrained in-plane compressive response of honeycomb core, a range of honeycomb cores was experimentally examined. Cores with a thin cell wall displayed extensive bending deformation of inclined cell walls while...
Show moreThis research focuses on deformation constraints of honeycomb core cells in a sandwich imposed by bonds to the face sheets. Specifically, the influence of one-sided core constraints on the bending stiffness of a single-face honeycomb core sandwich is examined. To characterize the unconstrained in-plane compressive response of honeycomb core, a range of honeycomb cores was experimentally examined. Cores with a thin cell wall displayed extensive bending deformation of inclined cell walls while cores with thicker walls failed by a shear-type instability of the cells indicated by tilting of vertical cell wall segments. The modulus and compressive strength of the core were compared to the predictions from unit cell models. The results show that geometrical imperfections such as deviation from the intended cell wall angle cause in-plane anisotropy and have strong influence on modulus and strength of the core. Modulus and strength were in reasonable agreement with predictions from unit cell models for cell wall modulus and strength between 5-12 GPa and 72-171 MPa for the set of cores examined.
Show less - Date Issued
- 2024
- PURL
- http://purl.flvc.org/fau/fd/FA00014438
- Subject Headings
- Honeycomb structures, Materials--Compression testing, Sandwich construction
- Format
- Document (PDF)
- Title
- Fatigue and fracture of foam cores used in sandwich composites.
- Creator
- Saenz, Elio., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This study focused on the fracture and fatigue crack growth behavior in polyvinylchloride (PVC) and polyethersulfone (PES) foams. A new sandwich double cantilever beam (DCB) test specimen was implemented. Elastic foundation and finite element analysis and experimental testing confirmed that the DCB specimen is appropriate for static and cyclic crack propagation testing of soft polymer foams. A comprehensive experimental mechanical analysis was conducted on PVC foams of densities ranging from...
Show moreThis study focused on the fracture and fatigue crack growth behavior in polyvinylchloride (PVC) and polyethersulfone (PES) foams. A new sandwich double cantilever beam (DCB) test specimen was implemented. Elastic foundation and finite element analysis and experimental testing confirmed that the DCB specimen is appropriate for static and cyclic crack propagation testing of soft polymer foams. A comprehensive experimental mechanical analysis was conducted on PVC foams of densities ranging from 45 to 100 kg/m3 and PES foams of densities ranging from 60 to 130 kg/m3. An in-situ scanning electron microscope study on miniature foam fracture specimens showed that crack propagation in the PVC foam was inter-cellular and in the PES foam, failure occurred predominately by extensional failure of vertical cell edges. Sandwich DCB specimens were loaded cyclically as well. For the PVC foams, the crack growth rates were substantially influenced by the density. For the PES foams, there was no clear indication about the influence of foam density on the crack growth rate.
Show less - Date Issued
- 2012
- PURL
- http://purl.flvc.org/FAU/3352829
- Subject Headings
- Sandwich construction, Composite materials, Fibrous composites, Strains and stresses, Management, Laminated materials, Plastics, Fatigue
- 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
- Study of edge effects in laminated sandwich specimens.
- Creator
- Mankuzhy, Pradeep Prabhakaran., Florida Atlantic University, Merry, Stephanie L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Different methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a...
Show moreDifferent methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a sandwich specimen in three point bending. However, these conventional methods failed to show the sharp strain gradient that exists near the free edge. The Force Balance Method was simplified for sandwich specimens by considering the face laminate as a homogeneous and orthotropic material with averaged properties. Simplified expressions were also obtained for calculating the boundary layer thickness. The boundary layer thickness was found to vary linearly with core thickness for the cases considered.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14523
- Subject Headings
- Sandwich construction--Fatigue, Composite materials, Strains and stresses, Structural analysis (Engineering)
- Format
- Document (PDF)
- Title
- Fatigue modeling of composite ocean current turbine blade.
- Creator
- Akram, Mohammad Wasim, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The success of harnessing energy from ocean current will require a reliable structural design of turbine blade that is used for energy extraction. In this study we are particularly focusing on the fatigue life of a 3m length ocean current turbine blade. The blade consists of sandwich construction having polymeric foam as core, and carbon/epoxy as face sheet. Repetitive loads (Fatigue) on the blade have been formulated from the randomness of the ocean current associated with turbulence and...
Show moreThe success of harnessing energy from ocean current will require a reliable structural design of turbine blade that is used for energy extraction. In this study we are particularly focusing on the fatigue life of a 3m length ocean current turbine blade. The blade consists of sandwich construction having polymeric foam as core, and carbon/epoxy as face sheet. Repetitive loads (Fatigue) on the blade have been formulated from the randomness of the ocean current associated with turbulence and also from velocity shear. These varying forces will cause a cyclic variation of bending and shear stresses subjecting to the blade to fatigue. Rainflow Counting algorithm has been used to count the number of cycles within a specific mean and amplitude that will act on the blade from random loading data. Finite Element code ANSYS has been used to develop an S-N diagram with a frequency of 1 Hz and loading ratio 0.1 Number of specific load cycles from Rainflow Counting in conjunction with S-N diagram from ANSYS has been utilized to calculate fatigue damage up to 30 years by Palmgren-Miner's linear hypothesis.
Show less - Date Issued
- 2010
- PURL
- http://purl.flvc.org/FAU/2867332
- Subject Headings
- Turbines, Blades, Materials, Fatigue, Marine turbines, Mathematical models, Structural dynamics, Composite materials, Mathematical models, Sandwich construction, Fatigue
- Format
- Document (PDF)