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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.8, #4)
Property Modeling across Transition Temperatures in PMC's: Part I. Tensile Properties by C. A. Mahieux; K. L. Reifsnider; S. W. Case (pp. 217-234).
Numerous studies report the effects of temperature on the stiffness and strength of polymer matrix composites (PMC's). Due to the complexity of the relaxation phenomenon in the matrix, these studies are mainly qualitative. In the present paper models were developed that can explicitly relate the mechanical response of the composite to temperature. These models are related to the microstructure of the constituents, and therefore can be applied to any polymer matrix composite. The possibility of using these models was illustrated by the study of the mechanical behavior of carbon fiber AS4/polyphenylene sulfide (PPS) at elevated temperatures. Part I of this paper relates to the modeling of the temperature-dependent composite tensile properties (stiffness and strength). Parts II and III focus on the life prediction of AS4/PPS undergoing static and fatigue end-loaded bending at elevated temperatures.
Keywords: polymer matrix composites; temperature; stiffness; strength; AS4/PPS
Property Modeling across Transition Temperatures in PMC's: Part II. Stress Rupture in End-Loaded Bending by C. A. Mahieux; K. L. Reifsnider (pp. 235-248).
The quasi-static properties (strength and stiffness) of polymer matrix composites (PMC's) exhibit significant temperature dependence in tension. Part I of the present paper introduced a new model enabling the computations of the strength and stiffness of PMC's in tension as an explicit function of temperature. In the second part, this model was used to model the behavior of unidirectional PMC's (AS4/PPS) in end-loaded bending. A new set of stress-rupture experiments was performed on the amorphous composite in bending in order to complete the data available in the literature (based on semi-crystalline composite). A model enabling the computation of the rupture life of the bent specimen as a function of temperature and applied load was established. The theoretical simulations were successfully compared to a set of 7 independent end-loaded bending experiments. This paper demonstrates the validity and the ease of integrating the polymer stiffness-temperature model in mechanics of composite materials, and completes the theoretical and experimental basis for the modeling of the end-loaded behavior of PMC's.
Keywords: polymer matrix composites; elevated temperatures; end-loaded bending; stress-rupture
Property Modeling across Transition Temperatures in PMC's: Part III. Bending Fatigue by C. A. Mahieux; K. L. Reifsnider; J. J. Jackson (pp. 249-261).
Parts I [1] and II [2] of the present paper introduced systematic models for the computation of thermal effects on strength and stiffness of unidirectional polymer matrix composites (PMC's) as well as the life prediction of these materials in end-loaded bending at elevated temperatures. The last step of this study was the possibility of introducing such models in durability codes such as MRLife [3]. A recent method was developed for the experimental characterization of end-loaded bending fatigue behavior of composites at elevated temperatures. The literature dealing with the durability of composite materials in bending focuses mainly on 3 and 4 point bending [4–6]. A limited set of data as well as the basis for theoretical modeling for fatigue end-loaded bending is available in the literature [7]. However, the life prediction scheme required elevated temperature experiments. New experiments in fatigue bending were performed in order to complete the available data. Microscopic observations revealed new information for the understanding of the damage process of unidirectional AS4/PPS composites in end-loaded fatigue bending. Finally, the models developed in Parts I and II were integrated into the MRLife integral enabling the life prediction of unidirectional PMC's under combined mechanical and thermal loads from room temperature experimental data.
Keywords: life prediction; durability; PMC's; AS4/PPS; temperature; fatigue; end-loaded bending; stress-rupture
The Influence of the Constituent Properties on the Residual Strength of Glare by T. J. de Vries; A. Vlot (pp. 263-277).
Aircraft manufacturers like Boeing and Airbus are currently designing new, high capacity aircraft, e.g., A3XX. To make this aircraft cost effective for the next 30 years, a strong impulse is given to the development of new technologies like the application of new aircraft materials. One of these studies investigates the feasibility of using the Fibre Metal Laminate Glare in the damage tolerance critical upper part region of the aircraft in order to reduce weight and increase safety. The present study investigates the crack resistance of Glare in case of foreign object damage as a function of the constituent's characteristics. An experimental program has been performed on Fibre Metal Laminates built up from several combinations of aluminium alloys and fibres. Especially the fracture mechanism was studied. It was found that a larger strain hardening region and a lower yield stress of the aluminium layers had a positive influence on the residual strength due to the capability of transferring high loads away from the cracked area. Increasing the stiffness and lowering the ultimate strain of the fibres reduces the residual strength, since stiffer fibres attract more load and because the final fracture is dominated by fibre failure.
Tensile Behaviour of Multilayer Knitted Fabric Composites with Different Stacking Configuration by Yanzhong Zhang; Zheng-Ming Huang; S. Ramakrishna (pp. 279-295).
In this paper, multilayer plain weft knitted glass fabric reinforced epoxy composite laminates with different stacking configurations, i.e., [0°]4, [0°/±45°/0°], [0°/90°/90°/0°] and [90°]4, were investigated experimentally. The laminates were uniaxially tensile loaded until final fractures occurred. The experimental results show that with the change in layer stacking structure, a corresponding variation in composite strength and stiffness was achieved. The tensile strength and modulus rank as follows: [0°]4 > [0°/±45°/0°] > [0°/90°/90°/0°] > [90°]4, which implicates a potential desiguability of Knitted Fabric Composites (KFC) for engineering applications. Failure behaviours of the fractured laminate specimens were examined using a ‘matrix digestion and layer peeling’ method, based on which the behaviour of each lamina in the laminate can be clearly shown. It was found that an angle-plied lamina in the laminate when subjected to a uniaxial tensile load has a different fracture mode from that of a single ply composite under an off-axial tensile load. This means that the lamina in the laminate is subjected to a more complicated load combination. By comparing the fractured mode of the latter lamina with that of the single ply composite, the load direction sustained by the lamina in the laminate can be identified, which provides a qualitative benchmark for verifying a theoretical simulation.
Keywords: knitted fabric composites; multilayer laminate; stacking configuration; mechanical properties; fracture mode; internal load direction; experimentation