Thermal Residual Stress Field Research Articles

Nanostructure characterisation of welded polyethylene using small angle X-ray scattering

Polyethylene (PE), a common thermoplastic polymer, is gaining prominence in the construction and packaging industries due to its exceptional mechanical properties, chemical resistance, safety, and integrity. However, internal defects can occur during manufacturing and throughout its service life. Neglecting this problem results in the disposal of plastic and, consequently, the accumulation of plastic waste and environmental issues, which have caused much criticism. A common method to repair the thermoplastics is welding, which introduces seams and localized thermal residual stress fields resulting in areas where damage can nucleate, potentially leading to cracks and failure over time. These cracks often start at the nanoscale and propagate to larger length scales until failure occurs. The objective of this research paper is to develop welding processes, with improved integrity and lifespan for PE. Additionally, it aims to investigate and assess the impact of PE welding on parent materials at nano- and micron-scales, to understand limitations that are challenging to overcome in such welding processes. The study involves joining PE panels together under various pre-heating and post-cooling conditions, followed by evaluating the environmental stress cracking resistance of the welds and the durability of the repaired components. The crystallinity and morphology of the PE material in the weld area and its surrounding regions were analysed using Small Angle X-ray Scattering (SAXS), and the findings were compared with results obtained from optical microscopy and Differential Scanning Calorimetry. The study concludes that SAXS results offer exceptional information about the parent PE and weld material within the welding zone.

Predictive Model for Thermal and Stress Field in Selective Laser Melting Process—Part II

Finite Element Analysis (FEA) is used to predict the transient thermal cycle and optimize process parameters to analyze these effects on deformation and residual stresses. However, the process of predicting the thermal history in this process with the FEA method is usually time-consuming, especially for large-scale parts. In this paper, an effective predictive model of part deformation and residual stress was developed for accurately predicting deformation and residual stresses in large-scale parts. An equivalent body heat flux proposed from the single layer laser scan model was imported as the thermal load to the layer by layer model. The hatched layer is then heated up by the equivalent body heat flux and used as a basic unit element to build up the macroscale part. The thermal history and residual stress fields of two solid parts with different support structures during the SLM process were simulated. Layer heat source method has the capability for fast temperature prediction in the SLM process, while sacrificing modeling details for the computational time-saving purpose. Thus numerical modeling in this work can be a very useful tool for the parametric study of process parameters, residual stresses and deformations.

Efficient predictive model of part distortion and residual stress in selective laser melting

Selective laser melting (SLM) is a promising technology to manufacture functional (end-use) metal parts with complex geometry directly from CAD data. The process induced high tensile residual stress and part distortion due to the non-uniform heat input during a SLM process would detrimentally affect the part performance. However, it is extremely challenging to predict distortion of a practical SLMed part if each single track is taken into account by using the conventional modeling methods The complex multiphysics phenomenon such as fluid flow in the melt pool, phase transformation during cooling, and resulted anisotropic properties further complicate this issue. In this study, a temperature-thread multiscale modeling approach has been developed to effectively predict residual stress and part distortion of a twin cantilever. An equivalent body heat flux has been proposed from the microscale laser scan model and imported as the “temperature-thread” to the subsequent mesoscale layer hatch model. The hatched layer is then heated up by the equivalent body heat flux and used as a basic unit to build up the macroscale part in a layer by layer fashion. The thermal history and residual stress fields of the twin cantilever during the SLM process were simulated. The predicted cantilever distortion agrees with the measured data with a reasonable accuracy.

Growth behavior of voids randomly distributed at grain boundary on thin metal film with bamboo microstructures under thermal residual stress field and electric field

Based on the rigid grain hypothesis, an analytic expression is developed to investigate the grain boundary void growth on a thin metal film with bamboo microstructures under thermal residual stress field and electric field. The effect of the microstructure of the thin metal film, thermal residual stress, applied electric field, and diffusivity ratio between the grain boundary and the interface on the growth behavior of the voids and the stress evolution is evaluated. The result shows that the thin metal film with fine grains near the anode end may inhibit void nucleation and growth, which is beneficial for the optimization design of the thin metal film with bamboo microstructures.

Stress Corrosion Cracking Analysis under Thermal Residual Stress Field Using S-FEM

Fracture in heat affected zone (HAZ) in welding has been a serious problem for the integrity of machines. Prediction of fracture behavior due to the residual stress field in HAZ is important. In this paper, S-Version FEM(S-FEM) is applied to simulate the crack growth under thermal and residual stress fields. For evaluation of stress intensity factor, virtual crack closure integral method (VCCM) is employed. In order to confirm the validity of this analysis, numerical results are compared with previously-reported analytical and experimental results. Then, crack growth analysis in piping structure with welding joint was conducted. The residual stress data was provided by JAEA, Japan Atomic Energy Agency, based on their numerical simulation. Using S-FEM, two- and three-dimensional analyses are conducted, and crack growth behavior under thermal stress field is studied and discussed.

Evaluation of the residual stresses due to the sintering process of diamond–metal matrix hot-pressed tools

The sintering process of diamond–metal matrix hot-pressed tools, usually used for cutting hard materials (e.g., stone cutting) originates residual stresses, which should be taken into account in the performance of the tool. The work concerns the use of finite element simulation for modelling of thermal residual stresses generated during the sintering process of metal matrix diamond tools normally employed by the industry. Stress distribution fields were determined for two different diamond shapes (modelled with 2D axisymmetric elements, with the sphere shape generated from the revolution of one circle and the octahedron shape generated from the revolution of one octagon, respectively) using an 8-node biquadratic axisymmetric quadrilateral, reduced integration element type CAX8. The thermal residual stress field in the nearby region of a diamond particle with the shape generated from the octagon is examined by using three different matrix materials, each one sintered at different temperatures. The analyses have demonstrated how much the residual stresses are sensitive to the stress–strain behaviour of the metal matrices.

Grain boundary void growth in bamboo interconnect under thermal residual stress field

An analytic expression is developed to predict grain boundary void growth in bamboo interconnect under thermal residual stress field. The rate process is controlled by grain boundary and interconnect/passivation interface diffusions. The thermal residual stress field relaxes during void growth. Based on the present analysis, the behaviors of the void growth and the stress redistribution are characterized as a function of the microstructure of the interconnect, the state of the thermal residual stress, the initial size of the void, as well as the diffusivity ratio between the interface and the grain boundary.

Thermal residual stresses in particulate composites and its toughening effect

In this paper, an accurate formula for calculating the thermal residual stress field in a particle-reinforced composite are presented. Numerical examples are given to show r-variations of the thermal residual stresses. The increase in fracture toughness of matrix predicted by the thermal residual stress field is compared well with the experimentally measured increase.

Interfacial Residual Stress Measurement of SiC/Epoxy Composites by Microphotoelastic Method

Interfacial residual stresses play an important role in the mechanical properties. In this paper, the interfacial residual stresses of SCI/Epoxy composites were determined using a novel technique-microphotoelastic method. The thermal residual stress field was also numerically simulated using a finite element software MSC.MARC. The difference and the similarities between the experimental results and the simulation of FEM analysis were discussed and the availability of the method was preliminarily certified.

Singular Thermal Residual Stress Field near the Interface Corner of Bonded Dissimilar Materials

In this paper, a cooled composite interface corner consisting of two bonded dissimilar materials is considered as a plane problem. With the complex variable method, the thermal residual stress field is studied analytically. It is found that the regular stress term possesses the singularity either of lnr or ln2r. The exact expressions for the corresponding singular stress field are presented.

Effects of the Thermal Residual Stress Field on the Crack Propagation in Graded Alumina/Zirconia Ceramics

A numerical approach to study the crack propagation in symmetric step-wise graded Alumina/Zirconia composites subjected to a residual stress field is presented in this work. The finite element method is used to calculate the stress intensity factor for cracks developing from the surface and to determine the effects of the thermal residual stresses. The results show that a suitably conceived stacking sequence induces in the laminate a residual stress field able to provide increased toughness and reliability of the structure by making the crack propagation stable below a given threshold stress. Moreover a lower bound on stress, below which no crack propagation occurs, can be identified.

A Voronoi cell finite element model for the indentation of graded ceramic composites

This paper presents a numerical approach, based on the Voronoi Cell hybrid Finite Element formulation, to the evaluation of the mechanical properties of Alumina/Zirconia graded composites. The computational model is based on two main features: (i) the discretization of the domain into homogeneous regions having geometrical features similar to those of the grains in each phase and (ii) the formulation of hybrid finite elements having polygonal shape and a non linear constitutive formulation which takes into account permanent strains and thermal effects. The purpose of the computational tool is to study the mechanical behaviour of layered graded materials subjected to contact loads on the surface. The analyses have shown that a stress redistribution and a lowering of the maximum tensile stress can be obtained by introducing a proper gradient of the mechanical properties of the ceramic composite. The results have shown that the effects of the thermal residual stress field, induced by the manufacturing process, must be taken into account for a proper assessment of the mechanical behaviour of the graded ceramic composites.

焼結ＳｉＣ繊維強化ＳｉＯ２‐ムライト複合材料の作製と特性評価

The sintered SiC fiber reinforced SiO2-mullite composites, which have three levels of added Al2O3 in the matrix, i.e., SiO2-3.7, 30, 50 mol%Al2O3, were synthesized by liquid state hot-pressing. Variation in the thermal residual stress fields in the composites caused by the difference in the thermo-mechanical mismatch between the fiber and matrices were investigated. The effects of the Al2O3 content in the matrix on the mechanical properties of the composites were then examined.The obtained composites had a very dense structure, and both the mullite and glassy SiO2 phases were found in the matrices. A higher Al2O3 content in the matrix lead to a higher mullite volume fraction. No chemical reaction among the constituents due to the fabrication process was observed.It was confirmed that the thermal residual stress field in the composites changed with an increase in the coefficient of thermal expansion of the matrix accompanied by an increasing Al2O3 content in the matrices.The network structure of the mullite crystals found in the SiC fiber/SiO2-30 mol%Al2O3 and SiC fiber/SiO2-50 mol%Al2O3 composites seemed to effectively prevent plastic deformation of the matrices during the flexural test at 1573 K.The SiC fiber/SiO2-30 mol%Al2O3 composite showed excellent mechanical properties up to 1573 K compared with previously reported ceramic matrix composites such as the SiC fiber/LAS composite or SiC fiber bonded ceramics in an inert atmosphere.

焼結ＳｉＣ繊維強化ＳｉＯ２‐ムライト複合材料のマトリックス亀裂発生ひずみと破壊挙動に及ぼす残留応力の影響

The sintered SiC fiber reinforced SiO2-mullite composites with matrix compositions, i.e., SiO2-3.7, 30, and 50 mol%Al2O3, had already been developed. In these composites, the thermal residual stress field changed with an increase in the coefficient of thermal expansion of the matrix accompanied by an increasing Al2O3 content (mullite volume fraction) in the matrices. A three-point flexural test was conducted for the composites at room temperature. The strain gauge method and AE monitoring were used to detect the matrix cracking strain during the test. The effect of the thermal residual stress on the matrix cracking strain and fracture behavior were investigated. The results are as follows.The matrix cracking strain observed in the composites with a higher tensile thermal residual stress in the matrix region parallel to the fiber axis was well predicted by the BHE theory. For the SiC fiber/SiO2-50 mol%Al2O3 composite, the first acoustic emission signal was detected just after the initial proportional limit of the stress-strain curve. For the other composites, the signals were detected below this limit. When the residual stress in the matrix region parallel to the fiber axis was compressive, the linear fracture behavior was found. On the contrary, the bi-linear fracture behavior was enhanced by the tensile residual stress in the matrix. This tendency agreed with the prediction method by Luh and Evans. The magnitude of the fracture energy obtained in each composite was qualitatively explained by the conventional theoretical formula.

The effect of particle shape on ductility of SiCp reinforced 6061 Al matrix composites

To study the effect of particle shape on thermal residual stress and strain distributions in composites, five two-dimension SiCp/6061Al model composites reinforced with spherical, hexagon, square, triangle and shuttle-shaped particles, respectively were analyzed by finite element method (FEM). The results showed that the particle shape has a great effect on thermal residual stress and strain fields in composites. There are a residual plastic strain concentration in the matrix around a pointed particle corner and a serious residual stress concentration in the pointed particle corner. The two concentrations increase with decreasing pointed corner degree. When an external stress is applied, the plastic strain concentration in the matrix around the pointed particle corner and the serious stress concentration in the pointed particle corner which will fracture on a relative low level of applied stress can decrease ductility of the composite. Two 6061 aluminium alloy matrix composites reinforced with general SiC particles and blunted SiC particles were studied on the basis of the FEM analyses. It was found that most very pointed particle corners are eliminated after SiC particles being blunted. Replacing general SiC particles with blunted ones can reduce residual plastic strain concentrations in the matrix and serious residual stress concentration in the particle. Therefore, blunted SiC particles reinforced composite shows a higher ductility than general one. (C) 1999 Elsevier Science S.A. All rights reserved.

The analysis of thermal residual stresses near the apex in bonded dissimilar materials

By employing the complex variable method and constructing the particular solution sequences in the form of complex functions, all the cases of the thermal residual stress field near the apex in dissimilar materials bonded with two arbitrary angles are researched theoretically, and the corresponding classical solutions are obtained. Moreover, the primary paradox, the secondary paradox and even the triple paradox are discovered in the classical solutions and also resolved here, thereby it is confirmed that thermal residual stresses near the apex in bonded dissimilar materials probably possess the singularities of lnr (when the primary paradox occurs) , ln2r (when the secondary paradox occurs) and even ln3r (when the triple paradox occurs) . In addition, the systematic method to solve multiple paradox problems is put forward. © 1999 Elsevier Science Ltd. All rights reserved.

Processing mechanics for flip-chip assemblies

In this paper, a non-linear finite element framework has been implemented to simulate the sequential build-up of a flip-chip package. A generalized deformation model with element removal and addition is used to activate and deactivate the underfill material layer to simulate flip-chip package fabrication. Using process models, one can determine the warpage stresses at any intermediate stage in the process. In addition, topological change is also considered in order to model the sequential steps during the flip-chip assembly. Geometric and material nonlinearity which includes the creep behavior of underfill and solder balls, and temperature-dependent material properties are considered. Different stress-free temperatures for different elements in the same model are used to simulate practical manufacturing process-induced thermal residual stress field in the chip assembly. This approach (the processing model established in this paper) is in contrast to the non-processing model employed by many researchers, which is shown to yield overly conservative and sometimes erroneous results, leading to non-optimal design solutions. From the finite element analysis, it is found that the strains and deflections obtained from the non-processing model are generally smaller than those obtained from the processing model due to the negligence of the bonding process-induced residual strains and warpage. Furthermore, the fatigue life for the outmost solder ball predicted by the processing model is much shorter than that predicted by the non processing model based on the Coffin–Manson equation. On the other hand, in order to prove the soundness of the framework established in this paper, the test results obtained by using the laser moiréinterferometry technique are compared with the results achieved from the proposed numerical analysis vehicle. It is shown that the deformation values of the flip-chip package predicted from the finite element analysis are in a good agreement with those obtained from the test.

Process Induced Stresses of a Flip-Chip Packaging by Sequential Processing Modeling Technique

In this paper, a nonlinear finite element framework was established for processing mechanics modeling of flip-chip packaging assemblies and relevant layered manufacturing. In particular, topological change was considered in order to model the sequential steps during the flip-chip assembly. Geometric and material nonlinearity, which includes the viscoelastic properties of underfill and the viscoplastic properties of solder alloys, were considered. Different stress-free temperatures for different elements in the same model were used to simulate practical manufacturing process-induced thermal residual stress field in the chip assembly. As comparison, two FEM models (processing model and nonprocessing model) of the flip-chip package considered, associated with different processing schemes, were analyzed. From the finite element analysis, it is found that the stresses and deflections obtained from nonprocessing model are generally smaller than those obtained from the processing model due to the negligence of the bonding process-induced residual stresses and warpage. The stress values at the given point obtained from the processing model are about 20 percent higher than those obtained from the nonprocessing model. The deflection values at the given points obtained from the processing model are usually 25 percent higher than those obtained from the nonprocessing model. Therefore, a bigger error may be caused by using nonprocessing model in the analysis of process-induced residual stress field and warpage in the packaging assemblies.

The effect of interphase on residual thermal stresses. 2. Unidirectional fiber composite materials

In real composite materials an additional phase may exist between the fiber and the matrix. This phase, commonly known as the interphase, is a local region that results from the matrix bonds with the fiber surface or the fiber sizing. The differing thermal expansions or contractions of the fiber and matrix cause thermally induced stresses in composite materials. In the present study, a four-cylinder model is proposed for the determination of residual thermal stresses in unidirectional composite materials. The elastic modulus of the interphase is a function of the interphase radius and thickness. The governing equations in terms of displacements are solved in the form of expansion into a series [1]. The effective elastic characteristics are obtained using the finite element approach. The effect of the interphase thickness and different distributions of the interphase Young's modulus on the thermal residual stress field in unidirectional composite materials is investigated.

Sequential processing mechanics modeling for a model IC package

In this paper, a nonlinear finite element framework was established for processing mechanics modeling of electronic packaging assemblies and layered manufacturing. In particular, topological change was considered in order to model the sequential steps during a typical integrated circuit (IC) package assembly. Geometric and material nonlinearity, temperature dependent material properties were considered. Different stress free temperatures for different elements in the same model were used to simulate practical manufacturing process-induced thermal residual stress field in the chip assembly. As comparison, two finite element method (FEM) models (processing model and nonprocessing model) of an encapsulated IC package considered, associated with different processing schemes, were analyzed. From the finite element analysis, it is found that due to the coefficient of thermal expansion (CTE) mismatch between the solder and silicon chip, the substrate and the solder, there exists very high stress field near these interfaces when the encapsulated IC package is cooled down to room temperature after processing for these two models. But in contrast with the stresses near the edges of all interfaces obtained from nonprocessing model, the stresses near the edges of all interfaces corresponding to processing model are generally higher than those obtained from nonprocessing model. In particular, the Von Mises stress at the edge of silicon chip/solder interface obtained from processing model is nearly 50% higher than that obtained from nonprocessing model. It is shown that processing model which is based on the FEM framework established in this paper can more realistically simulate a series of practical manufacturing processes in the chip assembly, whereas a larger error can be caused by using nonprocessing model in the analysis of process-induced residual stress field in the packaging assemblies due to the negligence of the bonding process during cooling from 250/spl deg/C to 160/spl deg/C.