Papers by Keyword: Material Property

Abstract: This study aimed at investigating the effects of the post material properties on the maximum stress in the root and maximum deformation of the restorative system. Effects of material properties of fiber post on the maximum equivalent stress in the root and the maximum deformation of the restorative system were numerically investigated. Results show that the maximum equivalent stress in the root can be decreased by 8.3% and the maximum deformation of the restorative system decreased by 10% compared with corresponding maximum values if changing Young’s modulus, Shear modulus and Poisson’s ratio in the range studied here. The maximum equivalent stress in the root is more sensitive to Young’s modulus and Poisson’s ratio while the deformation of the restorative system is more seriously affected by the Shear modulus of the post material.

Abstract: Single point incremental forming (SPIF) is a novel sheet metal forming process. Owing to unique deformation mechanism, this process improves the sheet formability as compared to the conventional stamping process. In the current paper, the mechanical properties and spifability (i.e. formability in SPIF) of a wide range of materials were tested. The mechanical properties were mainly determined through tensile testing and the spifability was evaluated using Varying Wall Angle Conical Frustum (VWACF) test. Each mechanical property was drawn against the improvement in sheet formability (i.e. difference of spifability and stampability) and the sole most influential property was identified. It was found that the improvement in formability increases with the increasing of true thickness strain at tensile fracture.

Abstract: Design engineers can choose from a large variety of materials in order to fulfill a certain function. In those fields of application with a lower level of complexity, it is often sufficient to manufacture the entire component in a “monolithic” manner from one single material. Concurrent, partly contradictory and, most probably, local requirements that must be fulfilled by a component often make material selection more difficult. As a consequence, it is often necessary to use several different materials with a local and functional orientation, which is a part of the multi-material design strategy. The potential of different materials can be used most effectively if this information is made available to the design engineers as early on in the design process as possible. The aim of the SFB 675 sub-project C7, therefore, is the development of a systematic design approach (Finite Element Design, FED) that focuses on finite component elements. As a result, the potential of the optimization of local properties is taken into consideration, and the interaction between the materials, production processes, and design can all be described.

Abstract: Generally, aspheric surfaces require extra high accuracy and roughness and need to be polished further after being shaped. Because the interaction between tool and work-piece in polishing process is compliant, rather than the kind of rigid cutting, the machining quality and machining process are closely allied to the physical properties of the work-piece material. A new three-degree-of-freedom hybrid position/force servo polishing system, which is based on universal CNC Lathe, is developed, and the effect of work-piece materials on the polishing process and processing quality of aspheric surfaces is studied after aspheric parts are compliantly polished in accordance with the Preston removal regulation in this paper.

Abstract: Electrically conductive polycrystalline composite diamond (EC-PCD) material, which consists of electrically conductive diamond grits, has recently been developed for the purpose of providing the material with both excellent tool property and machinability. This paper deals with the material property and the wear characteristics of EC-PCD. The result shows that the EC-PCD is superior in heat resistance compared with the conventional PCD. And the EC-PCD shows low frictional wear at high temperature in sliding test against stainless steel disk. Furthermore, in a cutting test of aluminum alloy, the EC-PCD cutting tool shows the same wear characteristics as the conventional PCD tool.

Abstract: In this study, optimal design of the aluminum electrical railcar under uncertainty of material property is performed. The main structure of the aluminum electrical railcar is composed of aluminum extruded panel. The yield strength and thickness of the aluminum extruded panel are treated as random variables. The loading conditions are based on the standard specification. Stress and resonant frequency are the design constraints and obtained through finite element analysis. The results of reliability-based design optimization considering the uncertainty of material property are compared to those of deterministic optimization.

Abstract: The objective of this study is to explore the influence of the steel’s material properties on the distribution of welding residual stresses of the butt-welded steel plate. First, S15C carbon steel’s material properties are varied in this study to calculate the corresponding welding residual stress by carrying out 3D finite element analyses. Results show the maximum longitudinal tensile residual stresses increase linearly with increasing thermal expansion coefficient and increasing yield stress. The length of the tensile residual stress zone decreases linearly with increasing thermal conductivity. Finally, based on the relationship between material properties and welding residual stresses, a useful prediction equation is developed and verified in this study.

Abstract: The fabrication of microelectronic and micromechanical devices leads to the use of only very small amounts of matter, which can behave quite differently than the corresponding bulk. Clearly, the materials will age and it is important to gather information on the (changing) material characteristics. In particular, Young’s modulus, yield stress, and hardness are of great interest. Moreover, a complete stress-strain curve is desirable for a detailed material characterization and simulation of a component, e.g., by Finite Elements (FE). However, since the amount of matter is so small and it is the intention to describe its behavior as realistic as possible, miniature tests are used for measuring the mechanical properties. In this paper two miniature tests are presented for this purpose, a mini-uniaxial-tension-test and a nanoindenter experiment. In the tensile test the axial load is prescribed and the corresponding extension of the specimen length is recorded, both of which determines the stress-strain- curve directly. The stress-strain curves are analyzed by assuming a non-linear relationship between stress and strain of the Ramberg-Osgood type and by fitting the corresponding parameters to the experimental data (obtained for various microelectronic solders) by means of a non-linear optimization routine. For a detailed analysis of very local mechanical properties nanoindentation is used, resulting primarily in load vs. indentation-depth data. According to the procedure of Oliver and Pharr this data can be used to obtain hardness and Young’s modulus but not a complete stress-strain curve, at least not directly. In order to obtain such a stress-strain-curve, the nanoindentation experiment is combined with FE and the coefficients involved in the corresponding constitutive equations for stress and strain are obtained by means of the inverse method. The stress-strain curves from nanoindentation and tensile tests are compared for two mate-rials (aluminum and steel). Differences are explained in terms of the locality of the measurement. Finally, material properties at elevated temperature are of particular interest in order to characterize the materials even more completely. We describe the setup for hot stage nanoindentation tests in context with first results for selected materials.

Abstract: The accurate prediction of welding distortion is an important requirement for the industry in order to allow the definition of robust process parameters without the need to perform expensive experiments. Many models have been developed in the past decades in order to improve prediction. Assumptions are made to make the models tractable; however, the consequences are rarely discussed. One example for such an assumption is the strain hardening model, which is often a choice between either kinematic or isotropic hardening. This paper presents the results of tensile tests for DP600 performed from room temperature up to one thousand degrees and for different strain-rates. In order to employ a mixed isotropic-kinematic hardening model, the fractions of each hardening contribution have been determined by means of bend testing. The welding distortion of a DP600 overlap joint has been simulated and it is shown that such a mixed-hardening model results in more accurate and reliable results.

Abstract: Today the numerical simulation of hot deformation processes is very advanced. But it requires mathematical models for metalphysical processes as for microstructure development, which take place during the deformation. Until now such models were developed for many steel grades and non-ferrous materials. For new steels as multi-phase steels laboratory investigations are required, in order to determine the optimal processing technologies of these materials. This applies also to the modelling. So far it is impossible, to calculate sole by mathematical solutions the manifold parameters of metalphysical processes and microstructure, for this reason laboratory trials and simulations are needed implicitly. Even for well known materials such procedures can be essential and useful. Using the multi-functional simulation system Gleeble HDS-V40 it is shown, which possibilities a physical simulation offers today. Starting with the annealing conditions, followed by microstructure development up to cooling, selected examples reflect the results of property development during hot deformation processes. The differences between conventional deformation after re-heating and deformation after direct-charging will be presented. The last-mentioned concept offers in its combination of near-netshape casting and direct charging special benefits, especially saving of energy.