Influence Of Thermal Residual Stresses Research Articles

The Effect of Thermal Residual Stress on the Stress State in a Short-Fiber Reinforced Thermoplastic

Upon their cooling and solidification, significant thermal residual stresses can develop in short-fiber reinforced thermoplastics due to the mismatch in coefficient of thermal expansion between fiber and matrix. In this study we set out to investigate this effect numerically. The build-up of thermal residual stresses is modeled by expanding a well-established constitutive model, the Eindhoven glassy polymer (EGP) model, with thermal expansion. The experimentally measured thermal residual stresses can be described using an effective glass-transition temperature and a constant coefficient of thermal expansion without the need for complex equilibrium kinetics associated with the glass transition itself. Subsequently, the influence of thermal residual stress on the deformation behavior for a short-fiber reinforced thermoplastic is studied employing multi-fiber representative volume elements (RVEs) for different fiber-weight fractions. The micromechanical models are evaluated on the importance of thermal residual stresses on the local and nominal stress state. From these analyses it can be concluded that the thermal residual stresses should be accounted for when assessing the quantitative local stress state and are therefore essential when local mechanisms are studied. In contrast, thermal residual stresses are not required to capture the nominal transient stress–strain response.

A multiscale interfacial cyclic debonding model for fibre-reinforced composites using micromechanics and molecular dynamics

In this study, a novel multiscale model based on the finite-volume direct averaging micromechanics (FVDAM) theory and molecular dynamics (MD) was developed to predict the interfacial cyclic debonding behaviour of composites. At the microscale, a solid interface with accumulated damage was incorporated using FVDAM, which enabled the simulation of both localised and homogenised interfacial damage responses under cyclic loading; a significant reduction in strength was observed after 10 loading cycles, implying the interfacial damage accumulation. At the atomic-scale, an interface model was built and subjected to cyclic loadings using MD simulation; the stress peak after 5 cycles was approximately half of the initial value, which provides damage parameters for upper-scale calculations and reveals the fundamental mechanism of interfacial cyclic debonding. The experimental data of unidirectional SCS-6/Ti-15-3 composites under cyclic loading were adopted to verify the proposed model. Furthermore, the influence of thermal residual stress and fibre orientation was investigated, which offers valuable insights for composite design and manufacturing.

Influence of Thermal Residual Stresses on the Behaviour of Metal Matrix Composite Materials

Influence of Thermal Residual Stresses on the Behaviour of Metal Matrix Composite Materials

Computational analysis of the influence of thermal residual stresses on the strength of metal-matrix composites

Deformation and fracture in metal-matrix composite materials is investigated during cooling followed by tension or compression. Microstructure of the composite comprising aluminum matrix and single boron carbide particle of irregular experimentally observed shape – is taken into account explicitly in calculations. Constitutive models describe isotropic elastoplastic and elastic or elastic-brittle behavior of the aluminum matrix and ceramic particles, respectively. Huber type fracture criterion takes into consideration the crack origination and growth in material local regions experiencing bulk tension. Developed numerical method used to simulate three-dimensional geometry of ceramic particles assumes the invariance of the mechanical fragmentation of rocks and brittle materials. Three-dimensional and plane-stress boundary-value problems in the dynamic formulation are solved numerically by the finite-element software package ABAQUS. Deformation of the composite subjected to tension from the initial undeformed state is compared to that produced by tension being a successor of the composite cooling from the recrystallization to room temperatures. Residual thermal stresses are found to increase the strength of the composite and change the fracture patterns from in-particle cracking to debonding.

Study of dynamic compressive behaviors of 2D C/SiC composites at elevated temperatures based on in-situ observation

Dynamic and quasi-static compressive behaviors of 2D C/SiC composites were examined from room temperature to 1600 °C based on in-situ observation, under the environment of air and argon. Tests were conducted respectively on a high temperature universal test machine and an improved high temperature split Hopkinson pressure bar. The improvement of the interface strength and the nucleation of multiple cracks influence the compressive strength under dynamic conditions. As the influence of thermal residual stress, the failure angles and compressive strength of the specimen increased with the increase of temperature in the argon environment. Owing to the competition between oxidation and thermal residual stress, the compressive strength of the specimen increased slightly with increasing temperature, and then dropped sharply for temperature above 700 °C in air. The strain rate sensitivity factor of 2D C/SiC composites increased significantly as the temperature increased in the air environment, but decreased in the argon environment.

Finite Element Analysis of the Crack Deflection in Fiber Reinforced Ceramic Matrix Composites with Multilayer Interphase Using Virtual Crack Closure Technique

Crack deflection along the interphase for fiber reinforced ceramic matrix composites (CMCs) is an important condition upon which the toughening mechanisms depend. The multilayer interphase is designed and developed to enhance this deflection mechanism. Combined with the virtual crack closure technique, a finite element model was proposed to predict the competition between crack deflection and penetration in multilayer interphase of CMCs. The model was used to analysis the propagation of primary matrix crack in a SiCf/SiCm composite with (PyC/SiC)n multilayer interphase. The effects of the number of sublayers, thicknesses of sublayers and thermal residual stress (TRS) on the energy release rate and the crack deflection mechanisms were studied. Results show that the multilayer interphase increases the ability to deflect the matrix crack at interfaces between sublayers. Moreover, the number of sublayers shows a larger effect than the thicknesses of the sublayers. The influence of TRS is much complex and needs to be evaluated accordingly. The research provides an analysis tool for promoting the toughening design of CMCs.

Micro-mechanical analysis of matrix crack-induced delamination in cross-ply laminates in tension

A two-dimensional representative volume element model is developed to study the micro-mechanics of matrix crack-induced delamination in cross-ply laminates under longitudinal tensile loading. Fiber-matrix debonding and matrix cracking are investigated in the 90° ply. The 0° plies are modelled as homogenized, anisotropic elastic solids. A special emphasis is put on the interlaminar region where a thick resin-rich area is explicitly established, and delamination is characterized by a coupled plastic-damage model of the matrix. The process of delamination initiated from the matrix crack tips is accurately revealed by finite element analysis. The impact of different damage mechanisms on the macroscopic mechanical responses is quantitatively captured. A parametric study is done on different cross-ply laminates with various thicknesses of 90° ply to study their effect on the variation of the homogenized longitudinal stiffness and transverse Poisson's responses. It is found that transverse Poisson's response is more sensitive to the damages in the laminate and that degradation of the responses in thicker laminates is severer. In addition, analysis of the influence of thermal residual stress shows that it changes the damage initiation location and evolution path, and affects the transverse Poisson's response more obviously.

The Influence of Thermal Residual Stresses on Mechanical Properties of Silicon Nitride-Based Composites.

In this work, two kinds of silicon nitride-based composites, namely, those with titanium nitride or silicon carbide additives, were sintered using the hot pressing technique (HP). The phase composition, microstructure, and mechanical and elastic properties of the materials were characterized. Three-dimensional geometric models of the composites were created on the basis of microstructure parameters. Using these models, bulk residual thermal stresses were calculated by the finite element method (FEM). Surface stresses were determined using the XRD method of sin2ψ.

Influence of thermal residual stresses on the free vibration of reinforced laminates

El uso de compuestos laminados se ha incrementado en la ingeniería moderna, fundamentalmente en proyectos en los cuales se requiere garantizar una adecuada resistencia y durabilidad. Se ha comprobado que algunas de las propiedades del material pueden ser afectadas por la aparición de tensiones residuales durante el proceso de manufactura. En este artículo, la influencia de las tensiones térmicas residuales en la vibración libre de compuestos laminados es analizada. Para el estudio experimental se empleó un laminado cuadrado de tipo pre-impregnado. El laminado fue reforzado usando dos tipos de refuerzos: laterales y perimetrales. Las placas fueron elaboradas usando dos diferentes técnicas: el primer tipo de laminados fue elaborado curando tanto la placa como los refuerzos a 177 °C de manera simultánea y posteriormente enfriados a la temperatura de servicio, mientras que para el segundo tipo de placas tanto las láminas como los refuerzos fueron preparados de forma independiente y pegados a temperatura de operación (22 °C). Un modelo numérico fue elaborado para comparar estos resultados con los resultados experimentales. Una buena precisión fue observada al comparar resultados numéricos y experimentales, mostrando que la presencia de tensiones térmicas residuales afecta el valor de las frecuencias naturales de vibración libre y la forma modal característica. Independientemente del tipo de refuerzo empleado, un notable incremento en estos valores fue observado, cuando el elemento se encuentra simplemente apoyado.

A virtual experimental approach to microscale composites testing

This paper presents a method for virtual testing composite microstructures with real fibre distributions, and compares the debonding and crack response with experimental results of identical microstructures under similar loading conditions. Prior to physical testing of HTA/6376 composite laminates, the fibre distribution of the undamaged physical specimen is automatically detected through image analysis and reconstructed as a 2D model in Abaqus software and tested following a sub-modelling approach. Once in-situ SEM micro-mechanical testing of the physical specimen is completed, the virtual and experimental crack paths can be directly compared to determine the viability of the virtual testing method. The influence of thermal residual stress on premature fibre-matrix debond initiation and crack propagation is also investigated. The results of the virtual testing presented in this paper give a strong correlation to the experimentally observed crack growth, where significant improvement on similar previously published virtual experimental results for composite materials in terms of both microstructure scale and accuracy of the crack representation, is observed. For the thermo-mechanically loaded models, thermal residual stresses were found to influence the crack path around certain fibres where localised thermal residual stresses were present, leading to a more accurate representation of damage than that given by the purely mechanically loaded models.

Tensile behavior of 2D-C/SiC composites at elevated temperatures: Experiment and modeling

In this paper, on-axis tensile behavior of a coated 2D-C/SiC composite at elevated temperatures was studied experimentally and theoretically. The measured data reveals that the tensile modulus and strength increase continuously with increasing temperature till 1273K. Contrarily, the failure strains decrease sharply at high temperatures than the counterpart at room temperature, manifesting the significant influence of thermal residual stresses (TRS) on mechanical behavior of C/SiC composites. Simulation of stress-strain response is based on a two-scale analytical model, in which the plain-weave element is idealized as a cross-ply laminate and its macroscopic mechanical parameters are evaluated by shear-lag approach. The primary calculation was concentrated on TRS of the composite. And, a new crack evolution model was introduced to describe the stochastic cracking process. The total strain response including residual strain and elastic strain from the loading-unloading-reloading conception was finally formulated through micromechanical analysis involving the influence of TRS on matrix cracking and interface debonding. Additionally, a strength model was developed for plain-weave structures by using shear-lag theory, statistical theory and rule of mixture. Both of the proposed constitutive and strength models can give accurate predictions for 2D-C/SiC composites at elevated temperatures.

Evolution of Voids in Mg/Al Diffusion Bonding Process

AbstractThe closure process of voids was very crucial for diffusion bonding, voids behaviors in Mg/Al bonding process were investigated, and the control mechanisms of diffusion at different predominant process parameters were discussed in this paper. Finite element simulation was utilized to investigate the influence of thermal residual stresses on the appearance of secondary voids. The results showed that: the dominant mechanism of void closure was plastic deformation in the initial stage of Mg/Al diffusion bonding. Numerical results indicated that secondary voids could be easily generated in the regions where tensile residual stress gradient achieves the maximum, corresponding to area that Al3Mg2 layer at the nearby Al/Al3Mg2 interface, the segregation of voids deteriorated the performances of the bonded joints.

Initial thermal stress and strain effects on thermal mechanical stability of through silicon via

This paper is concerned with the thermal mechanical stability of 3D TSV with initial thermal stress and deformation during working stage. Different from the previous results, integrated circuits (IC) packaging and fabricating process (PFP) is considered to obtain the initial thermal stress and strain for working stage. During the PFP of IC, the through silicon via (TSV) may go through several different processes, such as, making redistribution layer (RDL), reflow soldering, and filling under-fill. Since more than 70% of the PFP brings high thermal load, plastic deformation on TSV Cu is inevitable during PFP. The accumulation of the plastic deformation leads to thermal residual stress and strain at the beginning of working cycling stage. The thermal mechanical reliability and mechanism of the TSV were investigated by finite element (FE) method. The influence of thermal residual stress on the IC fatigue life was studied by comparing neglecting PFP (NPP) model with considering PFP (CPP) model. With different forms of plastic deformation and effective plastic strain accumulation during PFP, the lifetime is shortened at the middle part and prolonged in the TSV Cu interfacial line. The precision of evaluation and prediction the IC reliability was improved by CPP greatly, e.g. the minimal fatigue life of the TSV unit is 75cycles for NPP and 118cycles for CPP. With full consideration of the thermal mechanical mechanism related to the IC PFP, the fatigue life will be prolonged.

Micromechanical Modeling of Viscoplastic Behavior of Laminated Polymer Composites With Thermal Residual Stress Effect

In this paper, a multiscale approach has been developed for investigating the rate-dependent viscoplastic behavior of polymer matrix composites (PMCs) with thermal residual stress effect. The finite-volume direct averaging micromechanics (FVDAM), which effectively predicts nonlinear response of unidirectional fiber reinforced composites, is incorporated with improved Bodner–Partom model to describe the viscoplastic behavior of PMCs. The new micromechanical model is then implemented into the classical laminate theory, enabling efficient and accurate analysis of multidirectional PMCs. The proposed multiscale theory not only predicts effective thermomechanical viscoplastic response of PMCs but also provides local fluctuations of fields within composite microstructures. The deformation behaviors of several unidirectional and multidirectional PMCs with various fiber configurations are extensively simulated at different strain rates, which show a good agreement with the experimental data found from the literature. Influence of thermal residual stress on the viscoplastic behavior of PMCs is closely related to fiber orientation. In addition, the thermal residual stress effect cannot be neglected in order to accurately describe the rate-dependent viscoplastic behavior of PMCs.

Influence of thermal residual stress on behaviour of metal matrix composites reinforced with particles

The properties of a metallic matrix composites materials (MMC's) reinforced with particles can be affected by different events occurring within the material in a manufacturing process. The existence of residual stresses resulting from the manufacturing process of these materials (MMC's) can markedly differentiate the curves obtained in tensile tests obtained from compression tests. One of the themes developed in this work is the influence of residual stresses on the mechanical behaviour of these materials. The objective of this research work presented is numerically estimate the thermal residual stresses using a unit cell model for the Mg ZC71 alloy reinforced with SiC particles with volume fraction of 12% (hot-forging technology). The MMC's microstructure is represented as a three dimensional prismatic cube-shaped with a cylindrical reinforcing particle located in the centre of the prism. These cell models are widely used in predicting stress/strain behaviour of MMC's materials, in this analysis the uniaxial stress/strain response of the composite can be obtained through the calculation using the commercial finite-element code.

The influence of thermal residual stresses and thermal generated dislocation on the mechanical response of particulate-reinforced metal matrix nanocomposites

Due to thermal expansion mismatch between reinforcing particles and matrix, thermal induced dislocations are generated in metal matrix nanocomposites (MMNCs) during cooling down from the processing temperature. These dislocations have been identified as an important strengthening mechanism in particulate-reinforced MMNCs. In this study, the development of thermal residual stresses and thermal induced dislocations in MMNCs are predicted using discrete dislocation simulation, assuming the whole material is under uniform temperature change. Shear deformation is applied after the composites are cooled down to room temperature and the influence of thermal residual stresses and thermal generated dislocation on the overall response of particulate-reinforced MMNCs are investigated. The results show that the thermal residual stresses are high enough to generate dislocations and the dislocation density is higher in the interfacial region than the rest of the matrix. The predicted mechanical behavior of the MMNCs matches the experimental results better when thermal residual stresses are included in the simulations.

Initial damage induced by thermal residual stress and microscopic failure analysis of carbon-fiber reinforced composite under shear loading

In order to study the mechanical properties and the progressive failure process of composite under shear loading, a representative volume element (RVE) of fiber random distribution was established, with two dominant damage mechanisms – matrix plastic deformation and interfacial debonding – included in the simulation by the extended Drucker–Prager model and cohesive zone model, respectively. Also, a temperature-dependent RVE has been set up to analyze the influence of thermal residual stress. The simulation results clearly reveal the damage process of the composites and the interactions of different damage mechanisms. It can be concluded that the in-plane shear fracture initiates as interfacial debonding and evolves as a result of interactions between interfacial debonding and matrix plastic deformation. The progressive damage process and final failure mode of in-plane shear model which are based on constitute are very consistent with the observed result under scanning electron microscopy of V-notched rail shear test. Also, a transverse shear model was established as contrast in order to comprehensively understand the mechanical properties of composite materials under shear loading, and the progressive damage process and final failure mode of composite under transverse shear loading were researched. Thermal residual stress changes the damage initiation locations and damage evolution path and causes significant decreases in the strength and fracture strain.

ZrB2–SiC laminated ceramic composites

The oxidation behavior for ZrB2–20 vol% SiC (ZS20) and ZrB2–30 vol% SiC (ZS30) ceramics at 1500 °C was evaluated by weight gain measurements and cross-sectional microstructure analysis. Based on the oxidation results, laminated ZrB2–30 vol% SiC (ZS30)/ZrB2–25 vol% SiC (ZS25)/ZrB2–30 vol% SiC (ZS30) symmetric structure with ZS30 as the outer layer were prepared. The influence of thermal residual stress and the layer thickness ratio of outer and inner layer on the mechanical properties of ZS30/ZS25/ZS30 composites were studied. It was found that higher surface compressive stress resulted in higher flexural strength. The fracture toughness of ZS30/ZS25/ZS30 laminates was found to reach to 10.73 MPa m1/2 at the layer thickness ratio of 0.5, which was almost 2 times that of ZS30 monolithic ceramics.

Numerical Analysis of Thermal Residual Stress in Diamond Film Deposited on Molybdenum Substrate

In order to solve the problem of diamond film crack when deposited on molybdenum substrate to improve the preparation quality of diamond film and the rate of finished products , the distributions of thermal residual stress components in diamond film and at interface between the film and molybdenum substrate were simulated by finite element method in the case of whether to consider the plastic deformation of molybdenum substrate or not, moreover, the influence of thermal residual stress upon the failure of film was analyzed. Results show that thermal residual stress is more coincidental with experimental data when the plastic deformation of molybdenum substrate is considered. There are large tensile radial stress and tensile axial stress in the vicinity of upper surface of the film, which is the primary cause for the film to crack.

Influence of 211 particles on twin spacing in top-seeded melt-growth YBCO bulk superconductors

Influence of Y211 particles on the structure of {110} twins in single-grain YBCO bulk superconductors was studied by polarization light optical microscopy on the surfaces with small declination from the {110} plane. Used conditions allowed the observation of twin structure and twin spacing measurements at the twin spacing below the resolution limit of optical microscopy. Obtained results show that the twin spacing is proportional to the square root of the mean free distance between Y211 particles present in the samples. It is also shown that the twin complex size can be enormously high under the influence of thermal residual stresses.