https://repositorium.sdum.uminho.pt/bitstream/1822/19623/1/6.7.32%202012.pdf

Compliant contact force models in multibody dynamics : evolution of the Hertz contact theory

Metallographic Methods for Revealing the Multiphase Microstructure of TRIP-Assisted Steels - some applications for steels

A GA–DE hybrid evolutionary algorithm for path synthesis of four-bar linkage

Consistent and reasonable characterization of the material behavior under the coupled effects of strain, strain rate and temperature on the material flow stress is remarkably crucial in order to design as well as optimize the process parameters in the metal forming industrial practice. The objective of this work was to formulate an appropriate flow stress model to characterize the flow behavior of AISI-1045 medium carbon steel over a practical range of deformation temperatures (650⁻950 ∘ C) and strain rates (0.05⁻1.0 s - 1 ). Subsequently, the Johnson-Cook flow stress model was adopted for modeling and predicting the material flow behavior at elevated temperatures. Furthermore, surrogate models were developed based on the constitutive relations, and the model constants were estimated using the experimental results. As a result, the constitutive flow stress model was formed and the constructed model was examined systematically against experimental data by both numerical and graphical validations. In addition, to predict the material damage behavior, the failure model proposed by Johnson and Cook was used, and to determine the model parameters, seven different specimens, including flat, smooth round bars and pre-notched specimens, were tested at room temperature under quasi strain rate conditions. From the results, it can be seen that the developed model over predicts the material behavior at a low temperature for all strain rates. However, overall, the developed model can produce a fairly accurate and precise estimation of flow behavior with good correlation to the experimental data under high temperature conditions. Furthermore, the damage model parameters estimated in this research can be used to model the metal forming simulations, and valuable prediction results for the work material can be achieved.

Johnson Cook Material and Failure Model Parameters Estimation of AISI-1045 Medium Carbon Steel for Metal Forming Applications

Ground water geochemistry of Ballia district, Uttar Pradesh, India and mechanism of arsenic release.

Performance of EAs for four-bar linkage synthesis

The behaviour of typical armour steel material under large strains, high strain rates and elevated temperatures needs to be investigated to analyse and reliably predict its response to various types of dynamic loading like impact. An empirical constitutive relation developed by Johnson and Cook (J–C) is widely used to capture strain rate sensitivity of the metals. A failure model proposed by Johnson and Cook is used to model the damage evolution and predict failure in many engineering materials. In this work, model constants of J–C constitutive relation and damage parameters of J–C failure model for a typical armour steel material have been determined experimentally from four types of uniaxial tensile test. Some modifications in the J–C damage model have been suggested and Finite Element simulation of three different tensile tests on armour steel specimens under dynamic strain rate (10 −1  s −1 ), high triaxiality and elevated temperature respectively has been done in ABAQUS platform using the modified J–C failure model as user material sub-routine. The simulation results are validated by the experimental data. Thereafter, a moderately high strain rate event viz. Charpy impact test on armour steel specimen has been simulated using J–C material and failure models with the same material parameters. Reasonable agreement between the simulation and experimental results has been achieved.

Determination of Johnson cook material and failure model constants and numerical modelling of Charpy impact test of armour steel

In this paper, an experimental investigation on diode laser transmission welding of dissimilar thermoplastics between PMMA (polymethyl methacrylate) and ABS (acrylonitrile butadiene styrene) has been carried out. The effect of the laser welding parameters such as laser power, welding speed, stand-off distance and clamp pressure on weld strength and weld width is investigated using response surface methodology (RSM). Planned experiments and subsequent analyses are carried out to develop the mathematical models to establish the correlation between the process parameters and the responses. The adequacy of the developed models is tested using the sequential F -test, lack-of-fit test and the analysis-of-variance (ANOVA) technique. A numerical multi-objective simultaneous optimization technique, in which the RSM is incorporated, is used to find the optimum solutions, according to the desired optimization criteria. In addition to that, a graphical optimization technique is, also implemented which allow identifying a region in the graphic where optimal conditions lay on.

Experimental investigation on laser transmission welding of PMMA to ABS via response surface modeling

This study deals with simulation of low-cycle fatigue (LCF), followed by evaluation of fatigue parameters, which would be suitable for estimating fatigue lives under uniaxial loading. The cyclic elastic–plastic stress–strain responses were analyzed using the incremental plasticity procedures. Finite-element (FE) simulation in elastic–plastic regime was carried out in FE package ABAQUS. Emphasis has been laid on calibration of SS 316 stainless steel for LCF behavior. For experimental verifications, a series of low-cycle fatigue tests were conducted using smooth, cylindrical specimens under strain-controlled, fully reversed condition in INSTRON UTM (Universal Testing Machine) with 8,800 controller at room temperature. The comparisons between numerical simulations and experimental observations reveal the matching to be satisfactory in engineering sense. Based on the cyclic elastic–plastic stress–strain response, both from experiments and simulation, loop areas, computed for various strain amplitude, have been identified as fatigue damage parameter. Fatigue strain life curves are generated for fatigue life prediction using Coffin–Manson relation, Smith–Watson–Topper model, and plastic energy dissipated per cycle (loop area). Life prediction for LCF has been found out to be almost identical for all these three criteria and correlations between predicted and experimental results are shown. It is concluded that the improvement of fatigue life prediction depends not only on the fatigue damage models, but also on the accurate evaluations of the cyclic elastic–plastic stress/strain responses.

Material characterization of SS 316 in low-cycle fatigue loading

The micro mechanical model by Gurson–Tvergaard–Needleman is widely used for the prediction of ductile fracture. Some material properties (Gurson parameters) used as material input in this model for simulation are estimated experimentally from specimen level. In this article an attempt has been made to tune the values of some of these Gurson’s parameters by comparing the simulated results with the experimental results in the specimen level (axisymmetric tensile bar and CT specimens). An elastic–plastic finite element code has been developed together with Gurson–Tvergaard–Needleman model for void nucleation and growth. The initial value of f
c is determined from Thomason’s limit load model and then tuned on the basis of best prediction of the failure of one-dimensional tensile bar. Then the load versus load line displacement and J versus $${\Updelta}$$
 a results for CT specimen are generated with the same code and the value of f
n is tuned to match the simulated J versus $$\Updelta$$
 a results with the experimental results. Lastly the same code and the Gurson’s parameters obtained are used to simulate the load versus load point displacement and crack growth for pipe with circumferential crack under four point bending. The simulated results are compared with the experimental results to assess the applicability of the whole method. In the proposed material modelling, post-yielding phenomena and necking of the tensile bar are simulated accordingly and strain softening due to void nucleation and growth has been taken care of properly and drop in stress is implicitly simulated through a model. Incremental plasticity theory with arc length method is used for the nonlinear displacement control problem.

Sanjib Kumar Acharyya

Papers

Performance of EAs for four-bar linkage synthesis

Determination of Johnson cook material and failure model constants and numerical modelling of Charpy impact test of armour steel

Experimental investigation on laser transmission welding of PMMA to ABS via response surface modeling

Material characterization of SS 316 in low-cycle fatigue loading

A complete GTN model for prediction of ductile failure of pipe