In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is invest... more In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is investigated. For this purpose, four-point bending tests are simulated using both Classical Lamination Theory (CLT) and Finite Element Method (FEM) with brick elements. Unidirectional [θ6]s and balanced symmetric [θ3/-θ3]s composite laminates are considered and maximum allowable moment resultants as a function of fiber orientation angle, θ, are obtained using different failure criteria. The differences between the model predictions are discussed.
In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is invest... more In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is investigated by means of four – point bending tests. Four – point bending tests are modeled analytically using the classical lamination theory (CLT) and numerically using finite element method (FEM). Considering unidirectional [θ6]s as well as balanced symmetric [θ3/-θ3]s composite laminates, the maximum allowable moment resultant predictions of Tsai-Wu, maximum stress, maximum strain, Hashin, Tsai-Hill, Hoffman, quadric surfaces, modified quadric surfaces and Norris failure criteria, as a function of fiber orientation angle, θ, are obtained. Experiments are conducted for 0°, 5°, 15°, 30°, 45°, 60°, 75°, and 90° fiber angles and the differences between the model predictions and experimental results are discussed.
In this study, a new core design is introduced for sandwich composite structures. Its strength an... more In this study, a new core design is introduced for sandwich composite structures. Its strength and failure behavior are investigated via three-point bending tests. E-glass-fiber-reinforced epoxy resin is selected as the material for both the core and the face sheets. The core has an egg-crate shape. Acoustic emission (AE) method is used to detect the progression of damage. Signals due to elastic waves caused by activated damage mechanisms are investigated in order to identify the corresponding failure modes. A finite element model of the sandwich structure is developed to predict the failure behavior of the specimens under the loading conditions in the tests. A promising agreement between the results of the finite element model and the experiments is observed. The force-deflection-relation, the failure load as well as the region where damage initiates are accurately predicted.
In this study, failure behavior of fiber-reinforced composites under four-point bending is invest... more In this study, failure behavior of fiber-reinforced composites under four-point bending is investigated. First, the tests are modeled analytically using the classical lamination theory (CLT). The maximum allowable moment resultants of [θ12]T off-axis laminate as well as balanced and symmetric angle-ply [θ3/−θ3]s composite laminates as a function of fiber orientation angle, θ, are obtained using Tsai-Wu, maximum stress, maximum strain, Hashin, Tsai-Hill, Hoffman, quadric surfaces, modified quadric surfaces, and Norris failure criteria. Second, the same tests are simulated using the finite element method (FEM). Thermal residual stresses are calculated and accounted for in the failure analysis. An analysis is conducted for optimal positioning of the supports so as to ensure that intralaminar failure modes dominate interlaminar (delamination) failure mode. A test setup is then constructed accordingly and experiments are conducted. The correlation of the predicted failure loads and the e...
The crystallization behavior of thermoplastic composites during the tape placement process has be... more The crystallization behavior of thermoplastic composites during the tape placement process has been analyzed. A heat transfer analysis has been carried out using a finite element method. The heat transfer analysis is coupled with a crystallization kinetics model to predict the resulting morphology. In order to determine the heat intensity that could be applied to the laminate, a degradation kinetics model is added. The degradation kinetics model thus provides an upper bound for the heat input. The models relate the process parameters (e.g., roller velocity, roller pressure, heat input) to temperature and crystallinity distributions and degradation weight loss. These models are incorporated into a computer code to generate numerical results. By using this code, process conditions which are favorable to consolidation and also likely to produce optimum crystallinity levels are identified.
The main objective of the present study is to establish the relationships between the process var... more The main objective of the present study is to establish the relationships between the process variables and the quality of thermoplastic composite laminates fabricated by tape placement. The quality parameters considered in the process modeling are interlaminar bond strength, weight loss through thermal degradation, and crystallinity. Stress, heat transfer, crystallization, degradation, and bonding models are developed. These models relate the process parameters (e.g., roller velocity, roller pressure, heat input) to temperature, stress, and crystallinity distributions, degradation weight loss, and degree of bonding within the composite. These relationships are used to develop a process window to ensure product quality. The process parameters are then optimized to reduce the lay-up time.
Journal of Reinforced Plastics and Composites, 2017
Optimum structural design of composites is a research subject that has drawn the attention of man... more Optimum structural design of composites is a research subject that has drawn the attention of many researchers for more than 40 years with a growing interest. In this study, a review of the literature on this subject is presented. The papers are classified according to the type of the composite structure optimized in those studies, the loading conditions, the objective function, the structural analysis method, the design variables, the constraints, the failure criteria, and the search algorithm used by the researchers.
In this study, a concurrent design optimization methodology is proposed to minimize the cost of a... more In this study, a concurrent design optimization methodology is proposed to minimize the cost of a cold-forged part using both product and process design parameters as optimization variables. The objective function combines the material, manufacturing, and post manufacturing costs of the product. The part to be optimized is a simply supported I-beam under a centric load. Various constraints are imposed related to the performance of the product in use and the effectiveness of manufacturing. Nelder–Mead is used as search algorithm and analyses are conducted using commercial finite element software, ANSYS. Results show considerable improvement in the cost.
Box-shaped bumper beams are used in automotive industry as shock absorbers, which are subjected t... more Box-shaped bumper beams are used in automotive industry as shock absorbers, which are subjected to transverse impact loads during crash. In this study, hollow beams fixed to a vehicle by means of brackets are considered. The vehicle hits a wall with 40% offset by 50 km/h speed. The objective of this study is to increase the crashworthiness of the beam by maximizing the total energy absorbed by the beam during crash. The crash event is simulated using explicit finite element method. The design variables are the parameters defining the cross-sectional shape of the beam. The beam is optimized using a hybrid search algorithm combining genetic and Nelder & Mead algorithms. The results indicate significant improvement in the crash-worthiness of the bumper beams.
In this study, the progressive failure behavior of notched laminates under in-plane loads is mode... more In this study, the progressive failure behavior of notched laminates under in-plane loads is modeled to determine the ultimate failure load. Although numerous studies exist in the literature on this subject, correlations with the experimental results were examined qualitatively by comparing predicted and experimentally determined damage states. The final failure loads were also qualitatively determined by examining the predicted progression of damage state. In the present study, on the other hand, the final failure is quantitatively predicted. Successive finite element analyses of the part are carried out, while the load is incrementally increased. After each small load increment, failure of the material in each element is checked with the help of the maximum strain criterion. If the material fails for a given failure mode (fiber breakage, matrix cracking, or fiber-matrix shearing) according to the criterion, the respective material properties are degraded. Then, the overall stiffne...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2010
Composite materials have been used in many structural applications because of their superior prop... more Composite materials have been used in many structural applications because of their superior properties. Although composites are less sensitive to deformation, their increased use has emphasized that their deformation behaviours and hence deformation analyses are more complex than for structures of uniform composition. Deformation patterns contingent upon fatigue properties of composites may vary significantly because of the large differences in properties of the fibres and matrix, and the compositions of their sub-constituents. These complexities introduce major deficiencies to methods for composite materials, which often force large factors of safety to be adopted in designs. Consequently, composite structures used in fatigue applications are generally over-designed to eliminate catastrophic failure and are therefore heavier and more costly. Accordingly, the objective of this study is to develop a methodology to maximize the load-carrying capacity or strength of composite structur...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2009
Fillets are usually the most critical regions in mechanical parts especially under fatigue loadin... more Fillets are usually the most critical regions in mechanical parts especially under fatigue loading, considering that an increase in the maximum stress level considerably shortens the fatigue life of a part. The aim of this study is to find the best shape for a fillet in a shouldered shaft or plate so that the maximum equivalent stress has the lowest possible value. Optimization is achieved using a stochastic global search algorithm called the direct search simulated annealing. The boundary is defined using spline curves passing through a number of key points. The method is also applicable to shape optimization problems in which geometric constraints are imposed and, for this reason, tangential stress is not uniform along the optimal fillet boundary. Optimal shapes are obtained for flat and round bars subject to axial, bending, torsional, or combined loads. The results show that stress concentration factors close to one can be achieved even for bars with significant variations in cro...
In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is invest... more In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is investigated. For this purpose, four-point bending tests are simulated using both Classical Lamination Theory (CLT) and Finite Element Method (FEM) with brick elements. Unidirectional [θ6]s and balanced symmetric [θ3/-θ3]s composite laminates are considered and maximum allowable moment resultants as a function of fiber orientation angle, θ, are obtained using different failure criteria. The differences between the model predictions are discussed.
In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is invest... more In this study, failure behavior of fiber-reinforced composites under out-of-plane loads is investigated by means of four – point bending tests. Four – point bending tests are modeled analytically using the classical lamination theory (CLT) and numerically using finite element method (FEM). Considering unidirectional [θ6]s as well as balanced symmetric [θ3/-θ3]s composite laminates, the maximum allowable moment resultant predictions of Tsai-Wu, maximum stress, maximum strain, Hashin, Tsai-Hill, Hoffman, quadric surfaces, modified quadric surfaces and Norris failure criteria, as a function of fiber orientation angle, θ, are obtained. Experiments are conducted for 0°, 5°, 15°, 30°, 45°, 60°, 75°, and 90° fiber angles and the differences between the model predictions and experimental results are discussed.
In this study, a new core design is introduced for sandwich composite structures. Its strength an... more In this study, a new core design is introduced for sandwich composite structures. Its strength and failure behavior are investigated via three-point bending tests. E-glass-fiber-reinforced epoxy resin is selected as the material for both the core and the face sheets. The core has an egg-crate shape. Acoustic emission (AE) method is used to detect the progression of damage. Signals due to elastic waves caused by activated damage mechanisms are investigated in order to identify the corresponding failure modes. A finite element model of the sandwich structure is developed to predict the failure behavior of the specimens under the loading conditions in the tests. A promising agreement between the results of the finite element model and the experiments is observed. The force-deflection-relation, the failure load as well as the region where damage initiates are accurately predicted.
In this study, failure behavior of fiber-reinforced composites under four-point bending is invest... more In this study, failure behavior of fiber-reinforced composites under four-point bending is investigated. First, the tests are modeled analytically using the classical lamination theory (CLT). The maximum allowable moment resultants of [θ12]T off-axis laminate as well as balanced and symmetric angle-ply [θ3/−θ3]s composite laminates as a function of fiber orientation angle, θ, are obtained using Tsai-Wu, maximum stress, maximum strain, Hashin, Tsai-Hill, Hoffman, quadric surfaces, modified quadric surfaces, and Norris failure criteria. Second, the same tests are simulated using the finite element method (FEM). Thermal residual stresses are calculated and accounted for in the failure analysis. An analysis is conducted for optimal positioning of the supports so as to ensure that intralaminar failure modes dominate interlaminar (delamination) failure mode. A test setup is then constructed accordingly and experiments are conducted. The correlation of the predicted failure loads and the e...
The crystallization behavior of thermoplastic composites during the tape placement process has be... more The crystallization behavior of thermoplastic composites during the tape placement process has been analyzed. A heat transfer analysis has been carried out using a finite element method. The heat transfer analysis is coupled with a crystallization kinetics model to predict the resulting morphology. In order to determine the heat intensity that could be applied to the laminate, a degradation kinetics model is added. The degradation kinetics model thus provides an upper bound for the heat input. The models relate the process parameters (e.g., roller velocity, roller pressure, heat input) to temperature and crystallinity distributions and degradation weight loss. These models are incorporated into a computer code to generate numerical results. By using this code, process conditions which are favorable to consolidation and also likely to produce optimum crystallinity levels are identified.
The main objective of the present study is to establish the relationships between the process var... more The main objective of the present study is to establish the relationships between the process variables and the quality of thermoplastic composite laminates fabricated by tape placement. The quality parameters considered in the process modeling are interlaminar bond strength, weight loss through thermal degradation, and crystallinity. Stress, heat transfer, crystallization, degradation, and bonding models are developed. These models relate the process parameters (e.g., roller velocity, roller pressure, heat input) to temperature, stress, and crystallinity distributions, degradation weight loss, and degree of bonding within the composite. These relationships are used to develop a process window to ensure product quality. The process parameters are then optimized to reduce the lay-up time.
Journal of Reinforced Plastics and Composites, 2017
Optimum structural design of composites is a research subject that has drawn the attention of man... more Optimum structural design of composites is a research subject that has drawn the attention of many researchers for more than 40 years with a growing interest. In this study, a review of the literature on this subject is presented. The papers are classified according to the type of the composite structure optimized in those studies, the loading conditions, the objective function, the structural analysis method, the design variables, the constraints, the failure criteria, and the search algorithm used by the researchers.
In this study, a concurrent design optimization methodology is proposed to minimize the cost of a... more In this study, a concurrent design optimization methodology is proposed to minimize the cost of a cold-forged part using both product and process design parameters as optimization variables. The objective function combines the material, manufacturing, and post manufacturing costs of the product. The part to be optimized is a simply supported I-beam under a centric load. Various constraints are imposed related to the performance of the product in use and the effectiveness of manufacturing. Nelder–Mead is used as search algorithm and analyses are conducted using commercial finite element software, ANSYS. Results show considerable improvement in the cost.
Box-shaped bumper beams are used in automotive industry as shock absorbers, which are subjected t... more Box-shaped bumper beams are used in automotive industry as shock absorbers, which are subjected to transverse impact loads during crash. In this study, hollow beams fixed to a vehicle by means of brackets are considered. The vehicle hits a wall with 40% offset by 50 km/h speed. The objective of this study is to increase the crashworthiness of the beam by maximizing the total energy absorbed by the beam during crash. The crash event is simulated using explicit finite element method. The design variables are the parameters defining the cross-sectional shape of the beam. The beam is optimized using a hybrid search algorithm combining genetic and Nelder & Mead algorithms. The results indicate significant improvement in the crash-worthiness of the bumper beams.
In this study, the progressive failure behavior of notched laminates under in-plane loads is mode... more In this study, the progressive failure behavior of notched laminates under in-plane loads is modeled to determine the ultimate failure load. Although numerous studies exist in the literature on this subject, correlations with the experimental results were examined qualitatively by comparing predicted and experimentally determined damage states. The final failure loads were also qualitatively determined by examining the predicted progression of damage state. In the present study, on the other hand, the final failure is quantitatively predicted. Successive finite element analyses of the part are carried out, while the load is incrementally increased. After each small load increment, failure of the material in each element is checked with the help of the maximum strain criterion. If the material fails for a given failure mode (fiber breakage, matrix cracking, or fiber-matrix shearing) according to the criterion, the respective material properties are degraded. Then, the overall stiffne...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2010
Composite materials have been used in many structural applications because of their superior prop... more Composite materials have been used in many structural applications because of their superior properties. Although composites are less sensitive to deformation, their increased use has emphasized that their deformation behaviours and hence deformation analyses are more complex than for structures of uniform composition. Deformation patterns contingent upon fatigue properties of composites may vary significantly because of the large differences in properties of the fibres and matrix, and the compositions of their sub-constituents. These complexities introduce major deficiencies to methods for composite materials, which often force large factors of safety to be adopted in designs. Consequently, composite structures used in fatigue applications are generally over-designed to eliminate catastrophic failure and are therefore heavier and more costly. Accordingly, the objective of this study is to develop a methodology to maximize the load-carrying capacity or strength of composite structur...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2009
Fillets are usually the most critical regions in mechanical parts especially under fatigue loadin... more Fillets are usually the most critical regions in mechanical parts especially under fatigue loading, considering that an increase in the maximum stress level considerably shortens the fatigue life of a part. The aim of this study is to find the best shape for a fillet in a shouldered shaft or plate so that the maximum equivalent stress has the lowest possible value. Optimization is achieved using a stochastic global search algorithm called the direct search simulated annealing. The boundary is defined using spline curves passing through a number of key points. The method is also applicable to shape optimization problems in which geometric constraints are imposed and, for this reason, tangential stress is not uniform along the optimal fillet boundary. Optimal shapes are obtained for flat and round bars subject to axial, bending, torsional, or combined loads. The results show that stress concentration factors close to one can be achieved even for bars with significant variations in cro...
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