Behnam Salimi and David R. Hayhurst
Purpose — The purpose of this paper is to seek improved solution techniques for combined boundary‐initial value problems (IVPs) associated with the time‐dependent creep…
Abstract
Purpose — The purpose of this paper is to seek improved solution techniques for combined boundary‐initial value problems (IVPs) associated with the time‐dependent creep deformation and rupture of engineering structures at high temperatures and hence to reconfigure a parallel iterative preconditioned conjugate gradient (PCG) solver and the DAMAGE XXX software, for 3‐D finite element creep continuum damage mechanics (CDM) analysis.Design/methodology/approach — The potential to speed up the computer numerical solution of the combined BV‐IVPs is addressed using parallel computers. Since the computational bottleneck is associated with the matrix solver, the parallelisation of a direct and an iterative solver has been studied. The creep deformation and rupture of a tension bar has been computed for a range of the number of degrees of freedom (ndf), and the performance of the two solvers is compared and assessed.Findings — The results show the superior scalability of the iterative solver compared to the direct solver, with larger speed‐ups gained by the PCG solver for higher degrees of freedom. Also, a new algorithm for the first trial solution of the PCG solver provides additional speed‐ups.Research limitations/implications — The results show that the ideal parallel speed‐up of the iterative solver of 16, relative to two processors, is achieved when using 32 processors for a mesh of ndf = 153,238. Originality/value — Techniques have been established in this paper for the parallelisation of CDM creep analysis software using an iterative equation solver. The significant computational speed‐ups achieved will enable the analysis of failures in weldments of industrial significance.
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Z.P. WANG, D.R. HAYHURST, B.A. BILBY and I.C. HOWARD
Two non‐linear finite element programs have been restructured by using vectorization techniques in order to run efficiently on the Cray X‐MP/416. One of them has also been…
Abstract
Two non‐linear finite element programs have been restructured by using vectorization techniques in order to run efficiently on the Cray X‐MP/416. One of them has also been multi‐tasked to take advantage of the four processors of the machine. The techniques used in restructuring the software are discussed, and it is shown that each program must be treated individually. The resulting speed enhancements are shown to be program dependent, with a speed‐up of approximately 20 being achieved with one of the programs.
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Presents a review on implementing finite element methods on supercomputers, workstations and PCs and gives main trends in hardware and software developments. An appendix included…
Abstract
Presents a review on implementing finite element methods on supercomputers, workstations and PCs and gives main trends in hardware and software developments. An appendix included at the end of the paper presents a bibliography on the subjects retrospectively to 1985 and approximately 1,100 references are listed.
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Monojit Das, V.N.A. Naikan and Subhash Chandra Panja
The aim of this paper is to review the literature on the prediction of cutting tool life. Tool life is typically estimated by predicting the time to reach the threshold flank wear…
Abstract
Purpose
The aim of this paper is to review the literature on the prediction of cutting tool life. Tool life is typically estimated by predicting the time to reach the threshold flank wear width. The cutting tool is a crucial component in any machining process, and its failure affects the manufacturing process adversely. The prediction of cutting tool life by considering several factors that affect tool life is crucial to managing quality, cost, availability and waste in machining processes.
Design/methodology/approach
This study has undertaken the critical analysis and summarisation of various techniques used in the literature for predicting the life or remaining useful life (RUL) of the cutting tool through monitoring the tool wear, primarily flank wear. The experimental setups that comprise diversified machining processes, including turning, milling, drilling, boring and slotting, are covered in this review.
Findings
Cutting tool life is a stochastic variable. Tool failure depends on various factors, including the type and material of the cutting tool, work material, cutting conditions and machine tool. Thus, the life of the cutting tool for a particular experimental setup must be modelled by considering the cutting parameters.
Originality/value
This submission discusses tool life prediction comprehensively, from monitoring tool wear, primarily flank wear, to modelling tool life, and this type of comprehensive review on cutting tool life prediction has not been reported in the literature till now. The future suggestions provided in this review are expected to provide avenues to solve the unexplored challenges in this field.
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Guangcheng Dong, Xu Chen, Xinjian Zhang, Khai D.T. Ngo and Guo-Quan Lu
The purpose of this paper is to study the phenomenology of Al2O3-DBC substrate thermal-cracking under different high temperature cyclic loadings. The extremely low cycle fatigue…
Abstract
Purpose
The purpose of this paper is to study the phenomenology of Al2O3-DBC substrate thermal-cracking under different high temperature cyclic loadings. The extremely low cycle fatigue (ELCF) life prediction model for ductile materials was used to describe the thermal fatigue life of Al2O3-DBC substrates.
Design/methodology/approach
Four groups of thermal cycling tests using Al2O3-DBC substrates with 0.65 mm thick copper were conducted using different peak temperatures. The failure samples were observed by optical microscope. The thermal plastic strain distribution in the Al2O3-DBC substrates was analyzed using a finite element method with the Chaboche model for describing plastic deformation of copper. The ELCF life prediction model was used to predict the life of Al2O3-DBC substrates under high temperature cyclic loadings.
Findings
Interface cracking was observed to initiate at the short edge of the bonded copper and deviated into the ceramic layer when the crack grew beyond the critical length of 0.1-0.8 mm. The interface crack deviated into the ceramic layer at different thickness and grew parallel to the interface layer between the ceramic layer and copper layer. The crack propagation stopped after certain cycles. The copper layer with 10-20 μm thick alumina inside was not split away totally from the ceramic layer. The ELCF life prediction model could predict the life of Al2O3-DBC substrates well under high temperature cyclic loading. The material constants in the extremely low fatigue life prediction model were obtained using thermal fatigue tests results.
Research limitations/implications
The influence of copper layer thickness and ceramic layer thickness on thermal cracking characteristics of DBC substrate should be studied in the future. Failure models should also be further investigated.
Originality/value
The failure model of Al2O3-DBC substrates under high temperature cyclic loading was studied. A method for predicting the life of the substrate samples under high temperature cyclic loading was proposed.
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Jundong Yin, Baoyin Zhu, Runhua Song, Chenfeng Li and Dongfeng Li
A physically-based elasto-viscoplastic constitutive model is proposed to examine the size effects of the precipitate and blocks on the creep for martensitic heat-resistant steels…
Abstract
Purpose
A physically-based elasto-viscoplastic constitutive model is proposed to examine the size effects of the precipitate and blocks on the creep for martensitic heat-resistant steels with both the dislocation creep and diffusional creep mechanisms considered.
Design/methodology/approach
The model relies upon the initial dislocation density and the sizes of M23C6 carbide and MX carbonitride, through the use of internal variable based governing equations to address the dislocation density evolution and precipitate coarsening processes. Most parameters of the model can be obtained from existing literature, while a small subset requires calibration. Based on the least-squares fitting method, the calibration is successfully done by comparing the modeling and experimental results of the steady state creep rate at 600° C across a wide range of applied stresses.
Findings
The model predictions of the creep responses at various stresses and temperatures, the carbide coarsening and the dislocation density evolution are consistent with the experimental data in literature. The modeling results indicate that considerable effect of the sizes of precipitates occurs only during the creep at relatively high stress levels where dislocation creep dominates, while the martensite block size effect happens during creep at relatively low stress levels where diffusion creep dominates. The size effect of M23C6 carbide on the steady creep rate is more significant than that of MX precipitate.
Originality/value
The present study also reveals that the two creep mechanisms compete such that at a given temperature the contribution of the diffusion creep mechanism decreases with increasing stress, while the contribution of the dislocation creep mechanism increases.
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This paper develops C++ and Fortran-90 solvers to establish parallel solution procedures in a finite element or meshless analysis program using shared memory computers. The paper…
Abstract
Purpose
This paper develops C++ and Fortran-90 solvers to establish parallel solution procedures in a finite element or meshless analysis program using shared memory computers. The paper aims to discuss these issues.
Design/methodology/approach
The stiffness matrix can be symmetrical or unsymmetrical, and the solution schemes include sky-line Cholesky and parallel preconditioned conjugate gradient-like methods.
Findings
By using the features of C++ or Fortran-90, the stiffness matrix and its auxiliary arrays can be encapsulated into a class or module as private arrays. This class or module will handle how to allocate, renumber, assemble, parallelize and solve these complicated arrays automatically.
Practical implications
The source codes can be obtained online at http//myweb.ncku.edu.tw/∼juju. The major advantage of the scheme is that it is simple and systematic, so an efficient parallel finite element or meshless program can be established easily.
Originality/value
With the minimum requirement of computer memory, an object-oriented C++ class and a Fortran-90 module were established to allocate, renumber, assemble, parallel, and solve the global stiffness matrix, so that the programmer does not need to handle them directly.
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Guangcheng Dong, Guangyin (Thomas) Lei, Xu Chen, Khai Ngo and Guo‐Quan Lu
Direct‐bond‐copper (DBC) substrates crack after about 15 thermal cycles from −55 to 250°C. The purpose of this paper is to study the phenomenology of thermal‐cracking to determine…
Abstract
Purpose
Direct‐bond‐copper (DBC) substrates crack after about 15 thermal cycles from −55 to 250°C. The purpose of this paper is to study the phenomenology of thermal‐cracking to determine the suitability of DBC for high‐temperature packaging.
Design/methodology/approach
The thermal plastic strain distribution at the edge of the DBC substrate was analyzed by using a finite element method with the Chaboche model for copper. The parameters of the Chaboche model were verified by comparing with the three‐point bending test results of DBC substrate. The thermal analyses involving different edge tail lengths indicated that susceptibility to cracking was influenced by the edge geometry of the DBC substrate.
Findings
Interface cracking was observed to initiate at the short edge of the bonded copper and propagated into the ceramic layer. The interface crack was caused by the accumulation of thermal plastic strain near the short edge. The edge tail can decrease the thermal strain along the short edge of the DBC substrate. Thermal cycling lifetime was improved greatly for the DBC substrate with 0.5 mm edge tail length compared with that without edge tail.
Research limitations/implications
The thermal cracking of DBC substrates should be studied at the microstructure level in the future.
Originality/value
Thermal cycling induced failure of DBC was analyzed. A method of alleviating the thermal plastic strain distribution on the weakest site and improving the thermal fatigue lifetime of DBC substrates under thermal cycling was proposed.
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Lyndsay M.C. Hayhurst, Holly Thorpe and Megan Chawansky