Дисертації з теми "Viscoplastic deformation"

This dissertation presents the development of an anisotropic viscoplastic continuum damage model to describe the permanent deformation of asphalt pavements. The model is developed to account for several phenomena that influence the permanent deformation of Asphalt Concrete (AC) at high temperatures. These phenomena include strain rate dependency, confining pressure dependency, dilation, aggregate friction, anisotropy, and damage. The model is based on Perzyna's theory of viscoplasticity with Drucker-Prager yield function modified to account for the microstructure anisotropy and damage. A parametric study was conducted to study the effect of key factors such as inherent anisotropy and damage on the model response. A preliminary investigation was conducted to demonstrate the capabilities of the model and its sensitivity to changes in the microstructure distribution and loading conditions. The model was used to describe laboratory experimental measurements obtained from the Federal Highway Administration (FHWA) Accelerated Loading Facility (ALF). The model had a good match with these experimental measurements. In particular, using the damage parameter, the model was able to capture the point at which AC experienced tertiary creep in a static creep test. A comprehensive experiment was conducted to systematically determine the model parameters and the evolution laws that describe AC hardening, anisotropy, and damage. The experiment consisted of a set of compressive triaxial strength tests conducted at three confining pressures and five strain rates. Based on these experimental measurements, the model was modified to include a nonassociated flow rule. The model was shown to capture the experimental measurements very well. Furthermore, an experiment was conducted to capture and characterize damage evolution in AC due to permanent deformation. AC specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures. X-Ray computed tomography and image analysis techniques were used to capture and characterize the evolution of cracks and air voids in the deformed specimens. Damage was found to be a localized phenomenon in the sense that there exists a critical section in an AC specimen that is mainly responsible for failure. The results of the damage experiment supported the damage evolution function proposed in the viscoplastic model.

The deformation behavior of unsaturated soil has been the subject of numerous experimental and theoretical investigations. However, this phenomenon is not fully understood. Problems, such as the adoption of the proper stress variables, reduction of suction inducing collapse, suction effect on soil stiffness, rate dependency and air trapped within the soil under rainfall infiltration still need additional studies. In the present studies, an elasto-viscoplastic model for unsaturated soil is used based on two stress variables: 1) the skeleton stress is adopted as the stress variable; 2) suction is incorporated into the constitutive model to describe the collapse behavior. In addition, to investigate the multiphase behavior of unsaturated soil, a three-phase coupled model has been proposed based on the Theory of Porous Media (TPM) and finite deformation theory. Van Genuchten type of equation is employed as a constitutive equation between the saturation and the suction. Three-dimensional multiphase simulations are carried out to reproduce the behavior of unsaturated soil during monotonic loading triaxial tests under drained and undrained conditions for water and air. Compared with experimental results and the simulated results, it is seen that the proposed formulation is very suitable to describe the mechanical behaviors of unsaturated soil. Cyclic behavior of unsaturated soil has attracted much attention during the past few years. An elasto-viscoplastic cyclic model for saturated soil is extended for modeling of unsaturated soil. Based on finite deformation theory, three-dimensional multiphase analyses for unsaturated soil under cyclic loading are presented. The simulations are verified with cyclic triaxial tests on unsaturated silty clay under undrained for water and air conditions. It shows that the proposed multiphase formulation can be used to simulate the behaviors of unsaturated soil under cyclic loading. The high expansiveness of bentonite is another significant problem in unsaturated soil mechanics. In this research, an elasto-viscoplastic model for unsaturated expansive soil has been developed. An evolutional equation is adopted for describing the absorption of water into interlayer of clay platelets. In addition, the internal compaction effect caused by swelling of clay unit is expressed with the expansion of overconsolidation boundary surface and static yield surface. Based on the model, one-dimensional finite element analysis is conducted to study the development of swelling pressure. Compared with experimental results and simulated results, it is found that the proposed model can reproduce the effects of dry density and initial water content on swelling behavior. Using the proposed swelling model, two-dimensional swelling behaviors of the waste barrier are simulated.
Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第13775号
工博第2879号
新制||工||1425(附属図書館)
25991
UT51-2008-C691
京都大学大学院工学研究科社会基盤工学専攻
(主査)教授 岡 二三生, 教授 松岡 俊文, 准教授 木元 小百合
学位規則第4条第1項該当

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
Permanent deformation or rutting is a major distress in asphalt pavements. To predict permanent deformation of asphalt mixtures the dynamic creep test is often used in laboratory, with the result presented in terms of the so called flow number. However, for this work it was performed the triaxial repeated permanent deformation load test, a confined test that better represents field conditions. The models that incorporate the flow number do not represent the main zone of the dynamic creep test result, denoted secondary region, in which the permanent deformation rate of growth is constant. In this work the Shift Model was used, which is a viscoplastic model that accesses the permanent deformation from the superposition principles, i.e., time-temperature superposition and time-stress superposition. Thus, the asphalt mixtures were tested under different loading conditions, temperature, load time and rest period, in order to assess three parameters of the test: parameter C, which indicates where the secondary region begins (parameter that governs the primary region of the test); the parameter α (alpha) is the slope of the secondary region; and the parameter B represents the level of permanent deformation of the secondary region. The results show that the TRLPD test is more severe than the conventional dynamic creep test. Nevertheless, the use of TRLPD test represents an advance in the understanding of the behavior of asphalt mixtures with respect to rutting performance, and has the advantage of allowing the use of results in computational simulations.
A deformaÃÃo permanente à um dos principais defeitos em pavimentos asfÃlticos. Para prever esta falha em revestimentos, por meio de ensaios laboratoriais, à frequentemente utilizado o ensaio de creep dinÃmico cujo resultado final à apresentado em termos do chamado flow number. No entanto, para este trabalho foi realizado o triaxial repeated load permanent deformation (TRLPD) test, que à um ensaio sob condiÃÃes de confinamento, a fim de melhor se aproximar das condiÃÃes encontradas em campo. Os modelos que incorporam o flow number nÃo representam a principal regiÃo de ensaio de creep dinÃmico, denominada regiÃo secundÃria, na qual o incremento de deformaÃÃo permanente cresce em valor constante. No presente trabalho utilizou-se o Shift Model, o qual à um modelo viscoplÃstico que avalia a deformaÃÃo permanente a partir da superposiÃÃo dos efeitos tempo-temperatura e tempo-tensÃo. Dessa forma, as misturas asfÃlticas foram testadas sob diferentes condiÃÃes de carregamento, temperatura, tempo de aplicaÃÃo de carga e perÃodo de repouso. Foram avaliados trÃs parÃmetros do ensaio em questÃo: o parÃmetro C, que fornece os dados de onde a regiÃo secundÃria se inicia (parÃmetro que governa a regiÃo primÃria do ensaio); o parÃmetro α (alfa), que à o aclive da regiÃo secundÃria; e o parÃmetro B, que representa o nÃvel de deformaÃÃo permanente da regiÃo secundÃria. Os resultados obtidos mostram que o ensaio TRLPD à mais severo do que o ensaio convencional de creep dinÃmico, porÃm considera-se que a utilizaÃÃo de ensaios confinados representa um avanÃo para o entendimento do comportamento das misturas asfÃlticas quanto à resistÃncia à deformaÃÃo permanente das mesmas, e este traz a vantagem de poder ser usado em simulaÃÃes computacionais.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.
Includes bibliographical references (p. 251-258).
Glassy polymers, such as polystyrene (PS), poly(methyl methacrylate) (PMMA) and polycarbonate (PC), are common engineering polymers that have found uses in consumer products ranging from portable computers and optical lenses, to automotive components and appliance housings. PMMA and PS are typically considered to be brittle polymers, since they fail in a brittle manner under low triaxiality conditions, such as under uniaxial tension. Polycarbonate is considered to be a more ductile polymer than PMMA and PS, since it will deform plastically under uniaxial tension. However, PC does exhibit brittle behavior under certain loading conditions, such as low temperatures, high strain rates, or highly (tensile) triaxial stress states. A technique used for reducing the brittleness (increasing the fracture toughness) of glassy polymers is rubber-toughening. The technology of rubber-toughening, which involves blending a small volume fraction (5-20%) of rubber particles with the homopolymer, has been used commercially since the 1940s, and has been of major importance to the plastics industry. The technology of rubber-toughening is qualitatively well understood, but quantitative tools to study the material response are still at an early stage of development. The purpose of this thesis is to develop numerical tools to investigate the mechanical behavior of rubber-toughened glassy polymers, with emphasis on rubber-toughened PC. To this end, several tools are developed.
(cont.) Three-dimensional micromechanical models of the heterogeneous microstructure are developed to study the effects of particle volume fraction on the underlying elastic visco-plastic deformation mechanisms in the material, and how these mechanisms influence the macroscopic [continuum-level] response of the material. A continuum-level constitutive model is developed for the homogenized large-strain elastic-viscoplastic behavior of the material. The model is calibrated against micromechanical modeling results for rubber-toughened polycarbonate. The constitutive model is used to study boundary value problems such as notched tensile bars, where a multi-scale modeling approach enables assessment of failure due to local stress and strain levels in the material. The results are compared to experimental studies to establish correlations between the continuum-level response of the material, and observed failure mechanisms in the material.
by Mats Danielsson.
Ph.D.

The computation of the macroscopic response of polycrystalline aggregates from the properties of their single-crystal is a main problem in materials mechanics. During the mechanical deformation processing, all the grains in the polycrystalline material sample are reoriented. A crystallographic texture may thus be developed which is responsible for the material anisotropy. Therefore, the modeling of the texture evolution is important to predict the anisotropy effects present in industrial processes. The formulation of polycrystals plasticity has been the subject of many studies and different approaches have been proposed. Ahzi and M'Guil developed a viscoplastic phi-model. This model takes into account the grains interaction effects without involving the Eshelby inclusion problems.In this thesis, the phi-model was applied to different crystallographic structures and under different loading conditions. The mechanical twinning has been taken into account in the model. The FCC rolling texture transition from copper-type to brass-type texture is studied. The shear tests in FCC metals are also studied. The predicted results are compared with experimental shear textures for a range of metals having a high SFE to low SFE. For BCC metal, we compare our predicted results with those predicted by the VPSC model. We study the slip activities, texture evolutions and the evolution of yield loci. We also present a comparison with experimental textures from literatures for several BCC metals under cold rolling tests. The model has also been extended to HCP metals. We predict the deformation behavior of the magnesium alloy for different interaction strengths. We also compare our predicted results with experimental data from literatures. We show that the results predicted by the phi-model are in good agreement with the experimental ones.

O presente trabalho tem como objetivo a caracterização experimental e modelagem constitutiva do comportamento de metais CFC (Cúbicos de Face Centrada) policristalinos quando submetidos a altas taxas de deformação. O material empregado no desenvolvimento do trabalho é uma liga de alumínio comercialmente pura: o alumínio AA1050. No âmbito da presente investigação, os experimentos são conduzidos à temperatura ambiente. O desenvolvimento experimental tem por objetivo evidenciar as principais características constitutivas que descrevem o comportamento macroscópico desta classe de metais quando submetidos a processos de deformação envolvendo altas taxas de deformação: (i) o endurecimento induzido pela deformação; (ii) o endurecimento induzido pela taxa de deformação; e (iii) a sensibilidade instantânea em relação à taxa de deformação. Para a caracterização de cada uma destes aspectos constitutivos, são realizados experimentos específicos utilizando equipamentos desenvolvidos, em sua maioria, no contexto da presente investigação. De forma geral, os experimentos consistem em ensaios de compressão envolvendo uma ampla faixa de taxas de deformação, variando desde condições quasi-estáticas a taxas na ordem de 104 s−1. Os resultados experimentais, juntamente com evidências experimentais macro e microscópicas disponíveis na literatura, dão suporte ao desenvolvimento de um modelo constitutivo elasto-viscoplástico. A formulação constitutiva segue uma abordagem semi-física, na qual a escolha das variáveis inelásticas e proposição de suas regras de evolução são qualitativamente guiadas por considerações metalúrgicas baseadas no acúmulo e organização de discordâncias O modelo proposto, embora consista em uma abordagem simplificada quando comparado a modelos de base física, é capaz de representar separadamente cada uma das características constitutivas destacadas anteriormente. Com base nos resultados experimentais aqui obtidos, o modelo elasto-viscoplástico proposto é então ajustado e posteriormente validado. Na sequência é desenvolvida a formulação numérica relacionada ao modelo proposto. A abordagem como um todo é inserida em um contexto de deformações finitas seguindo uma descrição Lagrangiana Total. O desenvolvimento numérico descreve o procedimento utilizado para solução de problemas de equilíbrio não lineares seguindo uma formulação incremental implícita empregando o método dos elementos finitos. Em um contexto local, é utilizado um esquema de integração implícito seguindo um mapeamento exponencial. A linearização das equações de mapeamento de retorno possibilita a derivação analítica do módulo tangente consistente. O modelo constitutivo, bem como o procedimento numérico, são utilizados para a solução de problemas numéricos clássicos como: ensaio de compressão em condições de deformações homogêneas, e compressão envolvendo contato com atrito. As simulações numéricas avaliam tanto a capacidade constitutiva do modelo proposto em descrever o comportamento de estruturas quando deformadas sob condições envolvendo elevadas taxas de deformação, quanto à eficiência do procedimento numérico a partir de análises de convergência Em conclusão, com o procedimento experimental adotado é possível evidenciar as principais características macroscópicas inerentes ao comportamento de metais quando submetidos a processos de deformação envolvendo altas velocidades. Além disso, com base nos resultados analíticos e numéricos, observa-se que o modelo constitutivo proposto é capaz de reproduzir de forma satisfatória os comportamentos evidenciados experimentalmente.
The present work aims at performing the experimental characterization and constitutive modeling associated with the mechanical behavior of polycrystalline FCC (Face Centered Cubic) metals when subjected to high strain-rate deformations. The material to be employed in the experiments is a commercially pure aluminum alloy: aluminum AA1050. Within the present investigation context, experiments are performed at room temperatures. The primary objective of the laboratory experiments is to assess the main constitutive features associated with the macroscopic mechanical behavior observed for FCC metals subjected to high strain-rate deformation processes: (i) strain-hardening; (ii) strain-rate-hardening; and (iii) instantaneous rate-sensitivity. In order to characterize each constitutive feature, experiments using equipments specifically devised to achieve the objectives are performed. The laboratory investigation consists of compression tests involving a wide strain-rate range, from quasi-static conditions to strain-rates of the order of 104 s−1. Experimental results together with micro and macroscopic experimental evidences available in the literature give support to the development of a elastic-viscoplastic model. The stress-strain formulation follows a semi-physical approach, in which inelastic variables and their evolution equations are qualitatively motivated by metallurgical considerations based on the storage and arrangement of dislocations. Although its simplified nature when compared to physically-based models, the proposed model is capable of representing separately each one of the constitutive features highlighted early In addition, in analogy to the stress-strain proposition, a model describing the material hardness evolution in terms of strain and strain-rate histories is also provided. Based on the obtained experimental results, the proposed elastic-viscoplastic and hardness evolution models are adjusted and then validated. The corresponding stress-strain numerical formulation is developed in a subsequent step. The approach as a whole is integrated into finite strain framework following a Total Lagrangian description. The procedure employed to solve nonlinear equilibrium problem follows an implicit incremental formulation implemented in the context of the finite element method. At a local level, an implicit integration scheme based on an exponential mapping is adopted. From linearization of return mapping equations, an analytical consistent tangent modulus is obtained. Both constitutive model and numerical approach are employed to simulated classical problems: a compression test involving homogeneous deformation and a compression test involving contact and frictional conditions. Numerical simulations evaluate the constitutive capabilities associated with the proposed model when predicting the structural behavior at high strain-rate loadings. Furthermore, numerical efficiency and robustness related to the present procedure are also assessed by means of convergence analysis. While the adopted experimental procedure gave fundamental evidences of the main macroscopic features inherent in the metallic material behavior when subjected to high strain-rate deformations, the analytical and numerical results demonstrated that the proposed constitutive model is able to suitably reproduce the observed behavior.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 185-193).
Amorphous polymers are important engineering materials; however, their nonlinear, strongly temperature- and rate-dependent elastic-viscoplastic behavior is still not very well understood, and is modeled by existing constitutive theories with varying degrees of success. There is no generally agreed upon theory to model the large-deformation, thermo-mechanically coupled response of these materials in a temperature range which spans their glass transition temperature. Such a theory is crucial for the development of a numerical capability for the simulation and design of important polymer processing operations, and also for predicting the relationship between processing methods and the subsequent mechanical properties of polymeric products. We have developed a large-deformation thermo-mechanically coupled elastic-viscoplastic theory for thermoplastic amorphous polymers and shape memory polymers which spans their glass transition temperature. The theory has been specialized to represent the major features of the thermo-mechanical response of three technologically important thermoplastic amorphous polymers - a cyclo-olefin polymer (Zeonex-690R), polycarbonate, poly(methyl methacrylate) and a representative thermoset shape memory polymer - in a temperature range from room temperature to approximately 40 C above the glass transition temperature of each material, in a strain-rate range of ~ 10-4 to 101 s-1, and compressive true strains exceeding 100%. Our theory has been implemented in the finite element program ABAQUS. In order to validate the predictive capability of our constitutive theory, we have performed a variety of macro- and micro-scale validation experiments involving complex inhomogeneous deformations and thermal processing cycles. By comparing some key features, such as the experimentally-measured deformed shapes and the load-displacement curves from various validation experiments against corresponding results from numerical simulations, we show that our theory is capable of reasonably accurately reproducing the results obtained in the validation experiments.
by Vikas Srivastava.
Ph.D.

Запропоновано конструкцію фрагменту порожнистої металевої лопатки вентилятора гофрового типу, враховуючи фактор зниження маси пера лопатки за рахунок конструктивно - технологічних рішень при збереженні експлуатаційних параметрів (властивостей статичної та динамічної міцності). Проведено порівняльний статичний та динамічний аналіз експлуатаційних навантажень лопатки вентилятора суцільної та порожнистої конструкції. На основі виконаного аналізу доведено доцільність вибраної конструкцію поперечного перерізу фрагменту порожнистої лопатки. Запропонована структура технологічного процесу виготовлення порожнистих лопаток, яка ґрунтується на поєднанні двох процесів - зварювання під тиском і формоутворення пера лопатки в ізотермічних умовах. Розроблено метод експериментально - аналітичної побудови кривих деформування на підставі випробувань на згин. Результати дослідження показали, що криві в’язкопластичного деформування матеріалів, можна використовувати для розрахунку технологічних процесів. За результатами відпрацювання комплексної технології виготовлення фрагменту порожнистої лопатки розроблено технічні рекомендації щодо реалізації процесів виготовлення порожнистих лопаток.

A major instrumented geosynthetic reinforced approach embankment was constructed to 5.5 m elevation above ground, with prefabricated vertical drains, over a soft compressible clay deposit at Leneghan, Newcastle, Australia in May 1995. The field monitoring of settlements for over six years shows that the embankment manifests significant creep. The instrumentation, field performance and the finite element analyses for predicting the long-term performance of this embankment are described in this thesis. The maximum settlement of 1.1 m was observed one year after the completion of construction. However, the embankment continued to settle at a rate of 0.4 mm/day for the next 5 years. The horizontal displacements of 0.09-0.14 m at various locations and the maximum reinforcement strains of 0.67% were recorded. A numerical model was developed to perform a fully coupled large deformation elasto-viscoplastic finite element analysis for this performance prediction based on creep model proposed by Kutter and Sathialingam (1992). The foundation soil was modelled with creep material behaviour using six noded linear strain triangular elements. A well-documented case history ??? Sackville embankment, New Brunswick, Canada was analysed using this model as a benchmark problem and the model was found to predict all the behaviour characteristics reasonably well. The results obtained from finite element analysis using this model are shown to be in reasonable agreement with the observed performance of Leneghans embankment in terms of settlements, horizontal displacements, excess pore pressures and geosynthetic strains. But, the prediction of settlements was less than satisfactory beyond April 1999. Finite element analyses were performed to study the sensitivity of this embankment behaviour on the variation of hydraulic conductivity values and geosynthetic reinforcement properties. This sensitivity study indicated that the kv variation, the kh/kv ratio and the nominal values of geosynthetic properties adopted in the benchmark analysis are reasonable enough for the long-term behaviour prediction.

A new model using a double-continuity relation for predicting the evolution of pair-correlation functions (PCFs) is presented. The proposed model was developed using statistical continuum theory and is employed to predict the viscoplastic behavior of polycrystalline materials. This model was built based upon the continuity relations and a double divergence law that guarantees the conservation of both orientation and mass; and also satisfies the field equations (equilibrium, constitutive, and compatibility) at every point of the polycrystalline material throughout the deformation process. In the presented model, motion of particles in the real space and rotation of crystallographic orientations in the Euler angle space is monitored using an iterative process assuming that all the amount of deformation is applied uniformly without taking into account the localization effects. To study the accuracy of the proposed model, a commercially pure nickel material was rolled to different amounts of cold work. Texture and statistical analyses of the experimental and simulated microstructures were carried out. For the texture analysis, pole figures, ODF sections, and volume fractions of some ideal orientations of cold-rolling were studied. For the statistical analysis, pair correlation functions (PCFs) were employed and the correlations (auto- and anti-correlations) between ideal orientations and also the coherence length were studied. Simulated results captured from the implementation of the new model are in good agreement with the experimental ones at low and medium rolling deformations (0 to 50% rolling reductions); however, at large levels of deformations (above 70% reductions), because of the formation of cell blocks and relevant inhomogeneity, the occurrence of ideal orientations and their correlation properties in the experimental microstructure is affected by grain subdivision phenomena. This causes distortions in the shape of crystallographic grains at large rolling reductions, and accordingly we observe larger errors in comparison of simulated and experimental microstructures.

Le forgeage à chaud est un procédé de formage des métaux utilisé pour former des matériaux qui sont difficiles à former à froid ainsi que pour réaliser des géométries complexes. La réduction de la limite d’élasticité à haute température et une augmentation subséquente de l’aptitude à la mise en forme constituent le principal mécanisme à l’origine du procédé. Les méthodes numériques constituent un moyen efficace de prédire les états de contrainte / déformation du produit à différentes étapes de la mise en forme. Bien que les méthodes classiques soient suffisamment précises pour fournir une représentation appropriée du procédé, elles ont tendance à être coûteuses en ressources informatiques. Cela limite leur utilisation dans des cas concret, en particulier pour des études d’optimisation du procédé. L’approche pseudo inverse (API), développée dans le contexte du forgeage à froid 2D axisymétrique, fournit une estimation rapide des champs de contrainte et de contrainte dans le produit final pour une forme initiale donnée. Dans ce travail, l’API est étendue pour inclure les effets thermiques et visco-plastiques dans le procédé de forgeage ainsi que dans le cas général 3D. Les résultats sont comparés aux codes commerciaux disponibles basés sur les approches classiques pour montrer l’efficacité et les limites de l’API. Les résultats obtenus indiquent que l’API est un outil assez efficace pouvant être utilisé à la fois pour des simulations 2D et 3D du forgeage à chaud
Hot forging is a metal forming process used to form difficult-to-form materials as well as to achieve complex geometries. The reduction of yield stress at high temperatures and a subsequent increase in formability is the primary mechanism that drives the process. Numerical methods provide an efficient means to predict the material yield and the stress/strain states of the product at different stages of forming. Although classical methods are accurate enough to provide a suitable representation of the process, they tend to be computationally expensive. This limits its use in practical cases especially for process optimization. Pseudo Inverse Approach (PIA) developed in the context of 2D axisymmetric cold forming, provides a quick estimate of the stress and strain fields in the final product for a given initial shape. In this work, the PIA is extended to include the thermal and viscoplastic effects on the forging process as well as to the general 3D case. The results are compared with commercially available software, based on the classical approaches, to show the efficiency and the limitations of PIA. The results obtained indicate that PIA is a quite effective tool that can be used for both 2D and 3D simulations of hot forging

碩士
義守大學
材料科學與工程學系
87
Molding is a very important step during the packaging processes of microelectronics. The gold wires between the chip pads and leadframe deform under the action of flow loading of molten transfer molding compound. Significant permanent displacements of the wires, which are termed “wire sweep”, may occur if deformation is inelastic during cooling to room temperature. Since the advances of micro-electronics technology, the power of IC devices is improved as the physical dimensions shrink. This results in the smaller distance between gold wires. If the wire sweep is sufficiently large, it may cause a short circuit due to touching of adjacent wires. This phenomenon may be one of the most important problems in the IC package. In order to estimate the wire sweep, the knowledge of flow load, viscoplasticity of the wire, as well as finite element analysis are necessary. To develop viscoplasticity theory, experiments of rate change and stress relaxation of gold wires are performed at room temperature and 175ºC. Experimental results at both temperatures are employed to establish the viscosity functions and temperature-dependent elastic-viscoplastic constants of a wire, respectively. Because the flow load of the molten molding compound during cavity filling stage are quite different, C-MOLD package will therefore be applied to investigate the suitable flow load. Finally, the ABAQUS finite element package, together with the flow loading and viscoplasticity theory of the wire, are employed to estimate the wire sweep of the wire bond in DIP28L packages.