Thermal Residual Stresses In Composite Research Articles

A Microscale Analysis of Thermal Residual Stresses in Composites with Different Ply Orientations.

Composites, such as fiber-reinforced plastics, are produced using layering prepregs with varying ply orientations to achieve enhanced mechanical properties. However, this results in intricate residual stresses, which are influenced by the forming process and ply orientation. In this study, three representative microscopic models-featuring discrete fiber and resin-represent unidirectional, cross-ply, and angle-ply laminates. These models underwent simulations under three different cooling histories using the finite element method. The findings suggest that ply orientation does not significantly influence temperature distribution. However, it significantly impacts the von Mises stress in the fiber closest to the interface between two stacked laminae. This differs from the inter-laminar stresses determined with the macroscopic lamination model. Apart from the free edge, which exhibits a complex stress distribution, the von Mises stress within a unit cell displays a recurring pattern. The magnitude of the von Mises stress decreases as the ply orientation angle increases and shifts when a temperature gradient is present throughout the composite's thickness. This study provides valuable insights into the mechanics of residual stresses at the microscopic level and highlights potential defect areas influenced by these stresses.

Effects of the coating system and interfacial region thickness on the thermal residual stresses in SiC f/Ti–6Al–4V composites

A three-dimensional finite element model was developed to study effects of the coating system and interfacial region thickness on the distributions of the thermal residual stresses in continuous SiC fiber reinforced Ti–6Al–4V composite. Three coating systems were applied in this study, that is, C coating, C/TiB 2 coating and without coating. The influence of the interfacial region thickness on the thermal residual stresses in the composite was analyzed with concerning the simple case of without coating. Some proposal was given for the interface structure design of the composites. With regard to the thermal residual stresses, the C coating is an advisable choice for the interface structure design of the continuous SiC fiber reinforced Ti–6Al–4V composites. And for the region of the interfacial region thickness from 1 μm to 3 μm, the thicker interfacial region can reduce most of the thermal residual stresses in composites and improve the axial tensile strength of the composite.

A finite-element analysis of the inelastic relaxation of thermal residual stress in continuous-fiber-reinforced composites

In an effort to develop a methodology for interpreting in situ high-temperature neutron diffraction measurements of thermal residual stresses in composites, a finite-element model was developed and the implications of various material and experimental parameters on the residual stress evolution were studied. The model composite comprised a continuous Al 2O 3 fiber, unidirectionally aligned in a NiAl matrix. The effects of temperature-dependent elastic, plastic or creep properties, fiber volume fraction and cooling/heating rates were explored on the relaxation mechanisms of the residual stress during an initial cooling and a subsequent heating. Thermal path-dependency in the stress evolution was investigated by comparing the cooling and re-heat cycles. The result shows that the effect of the time-dependent deformation (creep) becomes more significant as the fiber content increases and the cooling/heating rate decreases. Furthermore, the path-dependency in stress evolution becomes stronger (i.e. considering the actual thermal history in the model becomes more important) as the total inelastic relaxation increases during the cooling and/or the subsequent re-heating cycles due to; (i) the presence of creep in addition to plastic deformation, (ii) increased fiber volume fraction, and (iii) slower cooling/heating rates. It was also demonstrated that using an estimated stress-free temperature in elastic–plastic models can be problematic in predicting the high-temperature behavior due to; (i) the simple assumption of reduced Δ T, and (ii) the thermal path-dependency.

Carbon-fiber-reinforced YMAS glass-ceramic-matrix composites—IV. Thermal residual stresses and fiber/matrix interfaces

Unidirectional composites consisting of a glass-ceramic matrix reinforced with continuous carbon fibers, fabricated by hot-pressing, exhibit different fracture behavior according to the sintering thermal cycle. The thermal residual stresses in composites are determined from the mismatch in coefficients of thermal expansion and the thermomechanical characteristics of both fibers and matrix. An ultrasonic technique is used to determine the temperature at which, on cooling, residual stresses induce microcracking in the matrix. The influence of the mechanical stresses and physico-chemical reactions between the fibers and the matrix on the nature and the strength of the fiber/matrix interface is discussed.