Forming

A new roll-based process and machine for three-dimensional bending of profiles with symmetrical and asymmetrical cross-sections have been developed. Compared to conventional processes like stretch bending, the advantage of the Torque Superposed Spatial (TSS) bending is the kinematic adjustment of the bending contour, leading to higher flexibility and cost efficiency, especially in small batch production. To define the spatial geometry

Optimization of process parameters in sheet metal forming is an important task to reduce manufacturing cost. To determine the optimum values of the process parameters, it is essential to find their influence on the deformation behaviour of the sheet metal. The significance of three important process parameters namely, die radius, blank holder force and friction coefficient on the deep-drawing characteristics of a stainless steel axi-symmetric cup was determined. Finite element method combined with Taguchi technique form a refined predictive tool to determine the influence of forming process parameters. The Taguchi method was employed to identify the relative influence of each process parameter considered in this study. A reduced set of finite element simulations were carried out as per the Taguchi orthogonal array. Based on the predicted thickness distribution of the deep drawn circular cup and analysis of variance test, it is evident that die radius has the greatest influence on the deep drawing of stainless steel blank sheet followed by the blank holder force and the friction coefficient. Further, it is shown that a blank holder force application and local lubrication scheme improved the quality of the formed part.

As failure criterion for sheet metal forming, conventional forming limit diagrams (FLD) are often used. The FLD is a strain based criterion, which evaluates the principal deformations at failure. Different investigations show that the FLD is dependent on the forming history and strain path. However, this is not the case for forming limit stress diagrams (FLSD). For this failure criterion, the principal stresses at failure are determined by FEM simulation of the Nakazima-test. Both, the FLD and the FLSD experimental investigations provide the basis for the sheet metal failure criterion. In contrast, continuum damage mechanics describe the damage evolution in the microstructure with physical equations, so that crack initiation due to mechanical loading can be predicted. By using the Gurson–Tvergaard–Needleman (GTN) damage mechanical model, a failure criterion based on void evolution was examined in this work. The parameter identification for the damage model will be discussed. The investigations demonstrate that FLD is inapplicable for complex forming processes with strain path changes. The FLSD is better suitable than the FLD for multi step forming processes. Micro-mechanical damage modelling with the GTN model also shows acceptable formability predictions, in spite of its generally insufficient consideration of the effective deviatoric stress fractions. The quality of failure prediction using continuum damage mechanics models is able to be increased by applying a more suitable damage models and a modern overall-scale modelling approach.

It is accepted that linear enamel hypoplasias (LEHs), a specific type of enamel thickness deficiency, are related to periodic physiological disruptions to enamel matrix secretion during times that teeth are developing. Thus, LEHs are treated as general indicators of metabolic stress. Because the disruptions that cause LEHs affect only the portion of the crown that is in the process of forming, determining their locations allows researchers to reconstruct chronologies of stressful events. It is widely held that the many of the commonly used macroscopic methods for estimating the timing of LEHs are imprecise and do not conform to our current understanding of the process of enamel formation. The goal of the present study is to compare estimated ages of LEH formation produced by two of the most commonly used macroscopic methods to those derived from data in recent histological studies that include more precise information about the timing of crown formation across diverse human populations. These approaches are compared in two ways: 1) by creating a theoretical model using simulated LEHs and 2) empirically, by analyzing data collected on a sample of ancient Nubians from Semna South (present-day Sudan). Results indicate that the approach derived from histological studies provides significantly higher age estimates than the commonly used methods and this difference is particularly marked in early forming LEHs. The magnitude of this difference is large enough to produce divergent interpretation of bioarchaeological datasets and suggests that reevaluation of the methods used to estimate ages of LEH formation may be justified. Am J Phys Anthropol, 2008. © 2007 Wiley-Liss, Inc.

Correlation of rolling conditions, microstructure, and low-temperature toughness of high-toughness X70 pipeline steels was investigated in this study. Twelve kinds of steel specimens were fabricated by vacuum-induction melting and hot rolling, and their microstructures were varied by rolling conditions. Charpy V-notch (CVN) impact test and drop-weight tear test (DWTT) were conducted on the rolled steel specimens in order to analyze low-temperature fracture properties. Charpy impact test results indicated that the energy transition temperature (ETT) was below −100 °C when the finish cooling temperature range was 350 °C to 500 °C, showing excellent low-temperature toughness. The ETT increased because of the formation of bainitic ferrite and martensite at low finish cooling temperatures and because of the increase in effective grain size due to the formation of coarse ferrites at high finish cooling temperatures. Most of the specimens also showed excellent DWTT properties as the percent shear area well exceeded 85 pct, irrespective of finish rolling temperatures or finish cooling temperatures, although a large amount of inverse fracture occurred at some finish cooling temperatures.