Papers by Keyword: Material Model

Abstract: In this study, a dissimilar AA7075+25% vol. SiC composite and AA2014 was selected to understand the effect of temperature distribution in the HAZ region with a maximum reinforcement of 25% vol. of SiC in the AA7075 matrix. The friction and slip-stick mechanism were combined in the numerical 3D model and simulated with different process parameters. The peak temperature of the dissimilar aluminium AA7075+25% vol. SiC composite and AA2014 was simulated and predicted as 860 K maximum and 728 K minimum, respectively. The experimental results were obtained in real-time FSW interfaced with a calibrated K-type thermocouple in a DAQ system. The thermocouple was placed at 15 mm, 20 mm, and 25 mm from the weld centerline to obtain experimental temperatures that were extremely close to the numerical peak temperature. The error percentage between the experimental values and simulation values ranged from 2.38% to 13.41%.

Abstract: The paper deals with possible ways of defining the material model of fibre reinforced concrete as a material for structural design. The material model is a tool that can be used to describe response of material to the applied load. It usually includes several different parameters: strengths, ultimate deflections, deformation modules, fracture energy, etc. The paper deals with the problematic phases of tests that are necessary to create a material model, but which may not always provide relevant data. Due to the nature of the material (a fibre reinforced composite with a relatively brittle matrix), it is necessary to analyse separately the behaviour of the material before and after cracks when creating the material model.

Abstract: Objective of the present study is the definition of a material model accounting for fatigue damage and degradation. The model is formulated as a brittle damage model in the otherwise linear elastic framework. A stress driven damage evolution equation is derived from microplasticity considerations. The model is implemented as a user-defined material model into a commercial finite element program. In a comparison with experimental data in the low cycle fatigue regime, a good agreement with the numerical prediction is obtained.

Abstract: The material model for reinforcing bar takes a very important role in the seismic analysis of reinforced concrete structures. The seismic performance of the structural elements such as column will be overestimated if the inelastic buckling is not incorporated in the material model. The Monti-Nuti Model could consider the buckling effect properly. The critical slenderness and anisotropy were discussed which has an important effect on the seismic behaviors of the reinforcement. Then this paper proposed a modified Monti-Nuti Model for different types of reinforcing bars, such as carbon steel reinforcement and stainless steel reinforcement including inelastic buckling. Subsequently, the implementation of the modified Mont-Nuti Model in OpenSees was introduced. Through validating with the experimental curves, the numerical curves generated by the modified model verified its capability.

Abstract: In this paper, a new model named as “brace01” for steel brace is presented on the basis of experimental data on different types of steel struts. This model shows a peasant capability in the structural analysis of Concentrically Braced Frames. A brace is idealized as a pin-ended member with a plastic hinge located at its midspan. This expression of the model is proposed by combining the mechanical properties and the phenomenological characters. The model for steel brace is implemented in an effective way in OpenSees. The calibration of the material model is done by comparing the numerical curves generated by the numerical model with the experimental curves of pin-ended steel braces. The new model is proved applicable to practical Concentrically Braced Frame.

Abstract: Decades ago, an implantation of polymer into concrete has taken an effect in Concrete Polymer Composites, C-PC – new concrete classes and since that time a constant development polymers in concrete technology has been observed. The object of the study in short definition has been described and classified. The meaning of polymer better concrete as well as how polymer improves the concrete has been explained. It has been analyzed and stressed that the polymer function in concrete is much higher than one could deduct from their mass share. The reason for that is synergy effect – the result of cooperation of polymers with other components of concrete. The recognition and using of synergic effects is the main but not only one direction of research works. The polymer in concrete product to be attractive on the market should fit up away growing demands of application and be based on the current status of knowledge. It means persistent and online resolving Material Model – Performance Model relation. Long time study on the modelling of cement hydration and polymer hardening process in Polymer Cement Concrete proved how significant is the idea/theory in technology development. Currently great expectation has been demonstrated towards Water-Soluble Polymers, WSP as nanomodifier of great potentiality. Various types of polymers in various amounts can be used for C-PC; even the polymer of the same type can be differentiated by the structure of polymer chain (length, branching) – this creates almost unlimited area of the control performance of C-PC. Outcome of the past ASPIC and ICPIC Congresses confirms that the research efforts have been always oriented on the engineering results based on the material microstructure understanding. The role of polymers in concrete could be not overestimated.

Abstract: The paper deals with the identification of material model based on the internal variable. The model with one internal variable, which was average dislocation density, was considered. Identification was performed using inverse analysis (IA) of uniaxial compression tests. In this work IA was transformed to an optimization task and the goal function was defined as difference (in Euclid's norm) between measured and calculated parameters: loads in plastometric tests (used to identify flow stress) and stresses in stress relaxation tests (used to identify recrystallization kinetics). Exploring a possibility of making the identification more reliable by application the Sensitivity Analysis (SA) was the main objective of the work. The IA was preceded by SA of the model output with respect to the model parameters to select an efficient optimization algorithm and/or eliminate local minima. Selected results of identification for different materials are presented in the paper, as well.

Abstract: In the present study, the Bauschinger effect exhibited in the advanced high strength steel under cyclic bending and reversed bending deformation was examined by both the experimental approach and the finite element analysis. The cyclic tension-compression tests were first conducted for the DP590 steel sheet to determine the material constants required in the Yoshida-Uemori model used in the finite element simulations. Since the deformation mode occurred in the reversed bending tests is similar to that presented in the sheet metal passing across the draw bead or die corner, a three-point reversed bending test apparatus was also developed and the experiments were conducted in the present study. The reversed bending test results clearly demonstrate that the Bauschinger effect presents in the reversed bending process. It confirms that the cyclic reversed bending tests can be applied to examine the Bauschinger effect exhibited in the sheet metal forming process. The finite element analysis was also performed to simulate both the U-hat bending and cyclic reversed bending processes. The comparison of the simulation results with the experimental data reveals that the finite element predictions in both springback and reversed bending load are more accurate if the Yoshida-Uemori model is adopted. It implies that consideration of the Bauschinger effect is necessary in the sheet metal forming if a reversed loading path is present during the forming process.

Abstract: Metal forming simulations based on the finite element method are a frequently used tool for the prediction of the deformed shape, material state and reaction forces. The most critical prerequisite for any reliable result is a reasonable description of the constitutive behavior of the underlying material. The presented work focusses on the latter for the case of molybdenum via advanced formulations for the temperature and strain rate dependence. The quality of the results is compared for several approaches. Sheet metal rolling serves as an example application. Verification is based on comparison with data from industrial processes.

Abstract: A material model is developed that predicts the plastic behaviour of fully hardened 22MnB5 base material and the heat-affected zone (HAZ) material found around its corresponding resistance spot welds (RSWs). Main focus will be on an accurate representation of strain fields up to high strains, which is required for subsequent calibration of the fracture behaviour of both base material and HAZ. The plastic behaviour of the base material is calibrated using standard tensile tests and notched tensile tests and an inverse FEM optimization algorithm. The plastic behaviour of the HAZ material is characterized using a specially designed tensile specimen with a HAZ in the gage section. The exact location of the HAZ relative to the centre of the RSW is determined using microhardness measurements, which are also used for mapping of the material properties into an FE-model of the specimen. With the parameters of the base material known, and by assuming a linear relation between the hardness and the plasticity model parameters of base material and HAZ, the unknown HAZ parameters are determined using inverse FEM optimization. A coupon specimen with HAZ is used to validate the model at hand.