Effects Of Thermal Residual Stresses Research Articles

3D micromechanical analysis of thermo-mechanical behavior of Al2O3/Al metal matrix composites

In this paper an elastoplastic finite element model for studying the thermomechanical behavior of Al/Al2O3 particulate composites is proposed. 3D representative volume elements (RVEs) are created to model the microstructures of Al/Al2O3 composites and the finite element models generated from RVEs are used to study the mechanical and thermal expansion properties. In order to study the effect of thermal residual stresses, first the RVEs are simulated for cooling process from sintering temperature to room temperature and thermal residual stress are estimated for different mechanical behaviors of Al matrix. Next, the thermomechanical properties are examined with existing residual stresses. The predicted effective elastic moduli and the coefficient of thermal expansion are compared with the experimental results reported in literature. The FE results have good correlation with the experimental data and the effects of microstructural parameters, voids and properties of the constituents are further discussed. In order to study the influence of voids on the elasto-plastic behavior of composites, the Gurson–Tvergaard–Needleman (GTN) model is applied. The nucleation and growth of voids in composites, under uniaxial tension, is studied.

Effects of thermal residual stress on interfacial properties of polyphenylene sulphide/carbon fibre (PPS/CF) composite by microbond test

As a result of manufacturing processes, thermal residual stresses often occur in fibre-reinforced polymer composites and affect the fibre/matrix interface properties, e.g. interfacial shear strength (IFSS), which is commonly evaluated by the microbond test. In thermoplastic matrices, thermal residual stresses can be relieved by annealing. In this study, to examine the effect of thermal residual stress on IFSS, microbond tests on both air-quenched (control) and annealed polyphenylene sulphide/carbon fibre samples are conducted. Comparing the pull-out results of the control to the annealed samples subjected to six different annealing temperatures between 80 and 230 °C, it is found that the thermal residual stresses in the fibre axial and radial directions are reduced progressively below and can be neglected above 120 °C. Thermal residual stresses in the fibre direction can be calculated to explain the microbond test results and construct a master curve for the IFSS. Post-debond frictional shear stresses can also be analysed in terms of the calculated fibre radial thermal residual stresses and debonded fibre morphologies.

Residual Stresses in Intrinsic UD-CFRP-Steel-Laminates - Experimental Determination, Identification of Sources, Effects and Modification Approaches

This paper focuses on the reduction of process-related thermal residual stress in fiber metal laminates and its impact on the mechanical properties. Different modifications during fabrication of co-cure bonded steel/carbon epoxy composite hybrid structures were investigated. Specific examinations are conducted on UD-CFRP-Steel specimens, modifying temperature, pressure or using a thermal expansion clamp during manufacturing. The impact of these parameters is then measured on the deflection of asymmetrical specimens or due yield-strength measurements of symmetrical specimens. The tensile strength is recorded to investigate the effect of thermal residual stress on the mechanical properties. Impact tests are performed to determine the influence on resulting damage areas at specific impact energies. The experiments revealed that the investigated modifications during processing of UD-CFRP-Steel specimens can significantly lower the thermal residual stress and thereby improve the tensile strength.

Simulation of interface damage in metal matrix composites under off-axis loading using cohesive zone model

A finite element, micromechanical model is developed to predict the inelastic behavior of SiC/Ti composites subjected to off-axis loading using a three-dimensional representative volume element (RVE). The model includes the effects of manufacturing process thermal residual stresses together with interface damage and fiber coating. The cohesive zone model is used to consider the imperfect interface between the fiber and matrix. Introducing a unique failure criterion for various off-axis angles is the main novelty of this study. Apart from interface damage, plastic deformation of the matrix is also considered as another source of nonlinearity. Appropriate boundary conditions are imposed on the RVE to allow simultaneous application of a combined normal axial and transverse and axial shear loading plus thermal residual stresses. Results of the presented finite element model are compared with experimental data for stress–strain response, initiation of nonlinearity, and ultimate strength in various off-axis angles which show good agreement. Moreover, parametric studies are conducted to examine the effects of thermal residual stress and fiber volume fraction (FVF) on the mechanical response of the material.

The effects of thermal residual stresses and interfacial properties on the transverse behaviors of fiber composites with different microstructures

Abstract This study presents a new micromechanical model to investigate the effects of thermal residual stresses and interfacial properties on the transverse behaviors of SiC/Ti composites with different microstructures. In this model, the fiber-matrix interface is modeled by the bilinear cohesive zone model. The interface model is introduced into the generalized method of cells, which has the advantage of computational accuracy and efficiency. At the same time, the generalized method of cells is extended to consider thermal residual stresses within the fiber and matrix phases. Thermal residual stresses are found to have a significant influence on the transverse behaviors of the composites. Compared with the perfect interface, the transverse behaviors of the composites with weak interface bonding are much lower. Moreover, with the increase of fiber fraction, the stiffness of the composites increases before debonding occurs while the saturation stress decreases. The predicted results using the circular fiber model and considering thermal residual stresses are more consistent with the experimental values compared with the results using the square or elliptical fiber model. When the stress concentration factor is considered and the interface is weakly bonding, the strength predictions are much better than the results using the perfect bonding.

Initial and final failure strength analysis of composites based on a micromechanical method

In this paper, a micromechanical model for investigating initial and final failure surface of fiber-reinforced composites laminate is established. The Generalized Method of Cells, which effectively predicts the thermal stresses influence on stress–strain behaviors of fiber-reinforced composites, is combined with Von-Mises yield criterion to describe nonlinear stress–strain behaviors of composites laminate. The Tsai–Hill criterion is incorporated into the model for predicting failure strength of lamina and typical laminate in uniaxial tension and biaxial loading, respectively. The numerical simulations based on a micromechanical method are performed to study the effects of thermal residual stresses on initial and final failure strength. Results revealed that thermal residual stresses influence on failure strength of the UD lamina is closely dependent on fiber off-axis angles. The contribution of thermal residual stresses in the final failure surface of [0°/±30°/90°]2 laminate and [90°/±45°/0°]2 laminate can be ignored. The results in longitudinal for lamina and biaxial tensile loadings for [90°/±45°/0°]2 laminate show good agreement with the experimental data.

Investigation of the effect of thermal residual stresses on deformation of α-uranium through neutron diffraction measurements and crystal plasticity modeling

The strong thermoelastic–plastic anisotropy of single crystal, orthorhombic α-uranium leads to the generation of significant thermal residual stresses (TRSs) after cooling from the processing temperatures of polycrystals. The present study shows the effect that these TRSs have upon subsequent room temperature deformation after aging. In situ neutron diffraction strain experiments performed on specimens machined from a clock-rolled plate, combined with ex situ texture measurements and elastoplastic self-consistent polycrystalline plasticity modeling, provides the necessary information to quantify the relative strengths and activities of the various deformation mechanisms known to operate within α-uranium. The results demonstrate that the activation of hard slip modes is necessary in order to generate macroscopic flow at the stress levels observed experimentally. Although the thermal residual stresses do not drastically affect the “bulk” response, inclusion of the TRSs drastically improve the agreement between predicted and experimentally measured internal strain evolution and strongly alter the predicted slip and twinning mode activities. As such, modeling efforts to discern the roles of the various mechanisms must account for the presence of thermal residual stress. In agreement with prior crystal plasticity modeling efforts, the crystallographic texture and polarity of twinning mechanisms explain the tension–compression strength asymmetry observed in the material (i.e. significantly more of the soft {130} twinning mode is observed to occur during compression along the prior plate RD than tension along the same direction).

Numerical stress analysis in adhesively bonded joints under thermo-mechanical loading

The objective of this work is to evaluate the effect of residual thermal stresses, arising after assembling a single-lap joint at elevated temperature, on the inelastic thermo-mechanical stress state in the adhesive layer. The numerical analysis (FEM) employing linear and non-linear material models, with geometrical nonlinearity accounted for, is carried out. Simulating the mechanical response, the calculated thermal stresses are assigned as initial conditions to polymeric, composite and metallic joint members to reflect the loading sequence where the mechanical strain is applied to cooled-down structure. It is shown that the sequence of application matters and simulations with simultaneous application of temperature and strain give different result. Two scenarios for adhesive joints with composites are studied: joining by adhesive curing of already cured composite parts (two-step process) and curing the adhesive and the composite simultaneously in one-step (co-curing). Results show that while in-plane stresses in the adhesive are higher, the peaks of out-of-plane shear stress and peel stress (most responsible for the joint failure) at the end of the overlap are reduced due to thermal effects. In joints containing composite parts, the one-step joining scenario is more favorable than the two-step. The ply stacking sequence in the composite has significant effect on stress concentrations as well as on the plateau value of the shear stress in the adhesive.

Effect of Thermal Residual Stresses on Bonded Structures Containing Cold Expanded and Bolted Holes

The primary focus of this investigation is to determine the distribution of thermal residual stresses that result during composite bonding processes, and the effect on stresses generated during the subsequent cold expansion of holes. Residual stress measurements were carried out using neutron diffraction techniques. Results show that the cold expansion process resulted in radial compressive stresses 3-4 mm from the edge of the hole and there was no significant effect of thermal residual stresses from the bonding process on the cold expansion and bolted stresses.

Micromechanical modeling on the rate-dependent viscoplastic behavior of polymer composites with thermal residual stress effect

The research focuses on the effect of thermal residual stress on the rate-sensitive viscoplastic behavior of polymer matrix composites with various fiber cross-sectional shapes. Micromechanical analysis was then conducted to incorporate the inelastic deformation and thermal residual stress into the micromechanical properties of a repeating cell and obtained the macromechanical response of polymer matrix composites by using homogenization theory. The responses of AS4/Polyetheretherketone (PEEK) with circular, square, and elliptical fibers are predicted by the method above at 10−5, 10−1, and 100/s with respect to 15°, 30°, 45°, 60°, 75°, and 90° off-axis angles. The results show that the viscoplastic difference of the response for various fiber shapes becomes more evident with the increase of strain rate. The effect of thermal residual stress varying with off-axis angle is similar to the sinusoidal curve. Besides, the thermal residual stress provides the largest effect on the response with square fiber and the smallest effect on the response with elliptical fiber, which of the effect decreases with the strain rate increasing.

Modeling of elastoplastic behavior of stainless-steel/bronze interpenetrating phase composites with damage evolution

In this paper an elastoplastic finite element model for stainless-steel/bronze interpenetrating phase composites (IPCs) is proposed. 3D representative volume elements (RVEs) are created based on the microstructures of the stainless-steel/bronze IPCs and the corresponding finite element models are used to study the mechanical and thermal expansion properties. The predicted effective elastic moduli and coefficient of thermal expansion are compared with those obtained from micromechanics based homogenization methods. The Gurson–Tvergaard–Needleman (GTN) constitutive model is adopted to investigate the influence of voids located in the bronze phase on elastoplastic and evolutionary damage behavior of the IPCs under uniaxial tension. The FE results have very good correlation with the experimental data, and the effects of thermal residual stress, void growth and nucleation on the flow properties of the IPCs are discussed.

Effects of Interphase Damage and Residual Stresses on Mechanical Behavior of Particle Reinforced Metal-Matrix Composites

Mechanical behavior of aluminum matrix composites reinforced with SiC particles are predicted using an axisymmetric micromechanical finite element model. The model aims to study initiation and propagation of interphase damage subjected to combination of thermal and uniaxial loading. Effects of manufacturing process thermal residual stresses and interphase de-bonding are considered. The model includes a square Representative Volume Element (RVE) from a cylindrical unit cell representing a quarter of SiC particle surrounded by Al-3.5wt.%Cu matrix. Suitable boundary conditions are defined to include effects of combined thermal and uniaxial tension loading on the RVE. An appropriate damage criterion with a linear relationship between radial and shear stresses for interphase damage is introduced to predict initiation and propagation of interphase de-bonding during loading. A damage user subroutine is developed and coupled to the finite element software to model interphase damage. Overall Stress-strain behavior of particulate metal-matrix composite by considering residual stresses is compared with experimental data to estimate interphase strength. Effects of thermal residual stresses in elastic, de-bonding and plastic zones of composite system are discussed in details. Furthermore, parametric study results show high influence of interphase strength on the overall mechanical behavior of composite material.

Thermal residual stresses in SiC particle reinforced aluminium composites: a study by the Taylor-based nonlocal theory of plasticity

Strain gradient theories have been considered to be an effective means for capturing the size effects on ceramic particle-reinforced metal-matrix composites (MMCp), but the results predicted by them are significantly lower than the corresponding experimental data. One reason might be, that the thermal residual stresses caused by thermal contraction mismatch between the metal matrix and the ceramic particle were neglected in the numerical models. By incorporating the Taylor-based nonlocal theory (TNT) of plasticity, the finite element method (FEM) is applied in the present research, to investigate the effect of thermal residual stresses on the yield stress and average axial stresses of the aluminium matrix reinforced by silicon carbide particles (SiCp/Al). The elements of the matrix have been implemented in the ABAQUS finite element code through its USER-ELEMENT (UEL) interface for TNT plasticity. Some comparisons with the associated literature demonstrate that the numerical model with the thermal residual stresses is more in agreement with the experimental results.

Biaxial Yield Surface Investigation of Polymer-Matrix Composites

This article presents a numerical technique for computing the biaxial yield surface of polymer-matrix composites with a given microstructure. Generalized Method of Cells in combination with an Improved Bodner-Partom Viscoplastic model is used to compute the inelastic deformation. The validation of presented model is proved by a fiber Bragg gratings (FBGs) strain test system through uniaxial testing under two different strain rate conditions. On this basis, the manufacturing process thermal residual stress and strain rate effect on the biaxial yield surface of composites are considered. The results show that the effect of thermal residual stress on the biaxial yield response is closely dependent on loading conditions. Moreover, biaxial yield strength tends to increase with the increasing strain rate.

Analysis of a pull-out test with real specimen geometry. Part I: matrix droplet in the shape of a spherical segment

We compared two models of the pull-out specimen – the ‘equivalent cylinder’ and the platelet models in which the matrix droplet is represented as a set of thin parallel disks with the diameters varying along the embedded fiber to approximate the real droplet shape. Analytical expressions for the profiles of the fiber tensile stress and the interfacial shear stress have been derived for the matrix droplet in the shape of a spherical segment, including the effects of residual thermal stresses and interfacial friction. Using these expressions, we analyzed the process of crack initiation and propagation in the platelet model and investigated the effect of the specimen shape on the force–displacement curves. The interfacial stress near the loaded fiber end in the platelet model is higher than in the equivalent cylinder model, which gives rise to earlier crack initiation and smoother shape of the force–displacement curve. As a result, the calculated interfacial shear strength values may be underestimated by 10–20%, if the equivalent cylinder is used instead of the real droplet shape. A method of correction to the equivalent cylinder model in order to avoid this underestimation is proposed.

Thermal-induced residual stresses affect the lifetime of zirconia–veneer crowns

ObjectivesThe purposes of this study were to investigate the effects of thermal residual stresses on the reliability and lifetime of zirconia–veneer crowns. MethodsOne hundred and twenty eight second upper premolar zirconia–veneer crowns were manufactured for testing the initial strength (n=64) and under cyclic fatigue (n=64). Zirconia copings (YZ Cubes, VITA Zahnfabrik, CTE: alphac=10.5ppm/°C) were milled using a Cerec3 InLab (Sirona) machine and sintered to a final thickness of 0.7mm. Sixty-four copings were sandblasted with 105μm alumina particles (15s, 3cm distance, 45° angle, 0.4MPa pressure) in order to trigger a tetragonalmonoclinic transformation and to produce a rough surface. The copings were veneered using two different porcelains (VM9, VITA Zahnfabrik, CTE: alphaVM9=9.1ppm/°C, Lava Ceram, 3M ESPE, CTE: alphaLava=10.2ppm/°C) so to result in crowns with either high thermal mismatch (+1.4ppm/°C with VM9) and low thermal mismatch (+0.3ppm/°C with Lava Ceram). The porcelains were applied by the same operator and fired (VITA Vacumat 4000) according to the firing schedules defined by the manufacturers to a final thickness of 1.4mm (total crown thickness=2.1mm, core/veneer ratio=0.5). After the last glaze firing the crowns were cooled following a fast (600°C/min) or a slow (30°C/min) cooling protocol. The glazed crowns were submitted to a sliding-motion (0.7mm lateral movement) cyclic fatigue in a chewing simulator (SD Mechatronik) under 20kg (∼200N load) weight until failure (chipping) (n=16). The other half of the crowns were subjected to a compressive loading test in an universal testing machine (Instron model 4240) until failure at a cross-head speed of 0.75mm/min (n=16). The failure probability for initial strength and cyclic fatigue was performed using a Weibull distribution approach at a scale factor of n=16. ResultsThe compressive strength test showed a low sensitivity to detect reliability variations regarding thermal stresses created within the veneer layer of tested crowns. For cyclic fatigue, slow cooling resulted in statistically higher cycles to failure only for the crowns that presented a high thermal mismatch between core and veneer (VM9 group). Comparisons between veneers with high or low thermal mismatches showed statistically higher sigma0 for Lava Ceram-veneered crowns only when the groups were fast-cooled. SignificanceMinimizing the thermal residual stresses within the veneer through the use of a veneer with a closer CTE to the zirconia delays the failure of zirconia–veneer crowns. Slow-cooling increases the lifetime of crowns presenting large differences in CTE between the zirconia core and the veneering porcelain.

Effects of inter-fiber spacing and thermal residual stress on transverse failure of fiber-reinforced polymer–matrix composites

The effect of thermal residual stress on transverse failure of fiber-reinforced polymer matrix composites is investigated by computational micromechanics with finite element method (FEM). Especially, the effect of inter-fiber spacing on thermal residual stress and then its effect on the transverse failure of composites are studied through microstructures with random fiber distribution and controllable minimal inter-fiber spacing. The residual stress is supposed to be introduced by thermal contraction of both resin and fiber as a result of cooling from the curing temperature to room temperature. The calculated residual stresses generally increase with the increase of fiber volume fraction and decrease of minimal inter-fiber spacing. And initial matrix and interface damage may be induced by thermal residual stress, especially when the inter-fiber spacing is quite small. For the particular composite system studied and the assumed parameters, it is concluded that the existence of residual stress can have significant effects on the failure behavior of composite when subsequent external load is applied, obviously changing the damage initiation locus and damage evolution path, and causing significant decrease in the transverse strength of the composite. Generally, there is a trend of more significant decrease in the transverse strength for higher fiber volume fraction and smaller inter-fiber spacing. In conclusion, this paper reveals how inter-fiber spacing and thermal residual stress affect the transverse failure behavior of composites, and thus can provide some guidance for both design and analysis of composites when thermal residual stress is concerned.

On the specimen for interfacial fracture toughness evaluation of foam-core sandwich structures

Foam-core sandwich specimens for interfacial fracture toughness measurement are designed based on the prediction method of steady-state crack location in foam-core sandwich beams using the crack deflection model developed previously. This paper derives the necessary condition that the face sheet debonding grows along the interface between the face sheet and the core during the fracture toughness tests. The recommended specimen thickness ratios for several testing methods are presented. Finally, the physical meaning of the derived condition is explained, and the effect of residual thermal stresses on the condition is discussed.

Confined fracture behavior of bulk metallic glass-coated tungsten composite wires produced by continuously coating process

The effects of thermal residual stresses on the tensile fracture behavior of the bulk metallic glass (BMG)-coated composite wires have been investigated by fabricating a series of BMG composite wires at varies drawing velocity. It is found that the coating thickness increases with the increase of drawing velocity and the axial and radial thermal stresses of the composite wires increase with the increase of the coating thickness. The values of axial thermal stresses are comparable with the tensile strength difference between the composite wires and the tungsten wire. Due to the effects of radial thermal stresses, the fracture mode change from the unconfined cleavage fracture of pure tungsten wire to confined step-like fracture mode of composite wires.

Carbon fibre pullout under the influence of residual thermal stresses in polymer matrix composites

► The anisotropic property of carbon fibres has significant effect on thermal residual stresses. ► The residual thermal stress has a significant influence at frictional sliding stage of fibre pullout. ► The interfacial shear strength is not a constant and decreases with the fibre embedded length. ► The specific pullout energy increases with the embedded length. ► The specific pullout energy does not depend on the fibre radius. A single carbon fibre pullout from a polymer matrix under the influence of residual thermal stresses was numerically investigated in this paper. The finite element method was first applied to obtain the residual thermal stress components along the interface between the fibre and the matrix due to curing. Four typical carbon fibres, T300, AS4, T800HB-40B and IM7 with anisotropic properties embedded in epoxy matrix HY6010 were considered. A comparison study indicates that simplified isotropic fibre model would overestimate the compressive residual axial and interfacial radial stress by up to 30%. Therefore, the anisotropic material properties of the fibres should be considered in the theoretical study of carbon fibre pullout. The cohesive zone model was then used to study the single carbon fibre pullout test. The numerical results indicate that the residual thermal stresses have a significant influence on fibre pullout at the stage of frictional sliding after interfacial debonding, which leads higher specific pullout energy. The effects of interfacial bonding condition and the fibre geometry were investigated by a parametric study. An interesting finding is that the interfacial shear strength, which is defined as the ratio of the debonding force to the embedded area, is not a constant. It decreases with the increase in the fibre embedded length. In addition, the fibre pullout energy per unit interfacial area (specific pullout energy) increases with the embedded length due to the effect of residual thermal stresses and interfacial friction. But the specific pullout energy does not depend on the fibre radius, which means that reducing fibre radius alone would not enhance the fibre bridging effect.