Simulation entlang der Prozesskette: Vom Walzen bis zum Crash

The simulation of individual manufacturing steps including crash behavior has already been used successfully in the automobile industry and helps to save costs and time. Research institutes and their customers from industry expect another qualitative leap in the possibilities of simulation in which not only individual processes but the entire process chain is "integrally" simulated. The automobile requires increasingly shorter development times and lightweight construction solutions for weight reduction. Especially in the past decades sheet metal working has increased. Numerical simulations in modeling at different steps in production are today an important component of almost every development of processes and parts. The path from material production to finished product as a rule has several manufacturing steps. The resulting material properties are in an emphatic way limited by the manufacturing process of the semi-finished product and are modified at each individual step. The usual method of proceeding, to determine from tests the model parameters for each process step is costly and also inexact because the material properties often are site-dependent. An attractive alternative is therefore a general simulation of the overall process chain that follows in particular the material properties. Research in this direction at the Fraunhofer-Institut für Werkstoffmechanik IWM attempts to integrate individual simulation steps into a simulation chain. The discussion covers as examples some aspects of such a process chain simulation in terms of sheet metal components. Diagrams and graph

Minimal Resistance of Engineering Materials to Brittle Fracture as Predicted by Local Approach

Two basic concepts of brittle fracture are considered : the first involving stage-by-stage interatomic bonds decohesion at the crack tip, the second - microcrack coalescence. Quantitative evaluation has been made of the material threshold and minimal fracture toughness values which correspond to the above concepts. The paper presents the analysis of methods for the experimental evaluation of two main structure parameters, which govern the material fracture, and discloses their physical meaning. These are the characteristic distance and cleavage stress. It also considers the methods of a priori express-evaluation of the materials fracture toughness from their conventional mechanical characteristics

Weibull probability distribution for reactor steel 20MnMoNi55 cleavage fracture in transition temperature

This paper presents the results and methods used for determining of fracture toughness of reactor steel, denoted as 20MnMoNi55, typically used for structures working at low temperatures, in transition temperature area. In addition, the effect of test specimen geometry and temperature on fracture toughness was investigated in order to predict the fracture behavior and probability of failure. Failure probabilities (i.e. cleavage fracture) in the function of J(c) for large test specimens, CT100 and CT200 were determined based on the results obtained by testing of small CT50 specimens, for the purpose of direct savings and decreased costs of specimen testing. Failure probability, represented using Weibull distribution of experimental data, will provide a clear insight into material behavior at different temperatures. Other factors affecting the obtained test results will also be discussed

Material characterisation for reliable and efficient springback prediction in sheet metal forming

In this paper, a novel experimental-numerical methodology for an accurate prediction of springback after sheet forming is presented. An advanced phenomenological material models is implemented in the FE-code ABAQUS. It includes the Bauschinger effect, the apparent reduction of the elasticity modulus at load reversal after plastic deformation, the strain rate dependency and the elastic-plastic anisotropy and its evolution during the forming process. The required material parameters are determined from stress-strain curves measured in tension-compression tests. These tests are carried out with a special test rig designed to avoid buckling of the specimen during compression. The benefits of this procedure for springback prediction are demonstrated. Additionally, parameters for the phenomenological models are determined from texture simulations

Advanced SEM methods in fatigue and fracture research

Translated from Czech (Kovove Mater. 1998 (3) p. 193-199)SIGLEAvailable from British Library Document Supply Centre-DSC:9023.190(VR-Trans--8856)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Material characterization for simulation of sheet metal forming

Advanced material models from the Chaboche family are well suited to cover springback effects and strain rate sensitivity in sheet metal forming simulations. Experimental techniques (such as tension-compression tests and other tests), parameter identification, and applications to real parts will be presented together with first steps towards virtual materials testing by means of texture simulations. Materials ivestigated range from different mild and high strength steels to magnesium sheet tested at elevated temperatures

Characterizing the evolution of physical properties and mixing state of black carbon particles: from near a major highway to the broader urban plume in Los Angeles

Black carbon (BC) particles can have deleterious human health consequences and impact regional and global climate. Uncertainties remain in part due to incomplete knowledge on the evolution of physical properties and mixing state of black carbon from sources to the remote atmosphere. We aim to understand how road-to-ambient processing and longer timescale aging in an urban plume affect black carbon physical properties. Refractory black carbon (rBC) was measured during summer 2016 using a single-particle soot photometer (SP2) in two distinct environments: near a major freeway and downwind of downtown Los Angeles. The near-road measurements were made at distances ranging from 30 to 114&thinsp;m downwind of Interstate 405 in Los Angeles. These results were compared with measurements performed 100&thinsp;km east of Los Angeles in Redlands, California. Coatings on rBC particles were quantified using two methods. As distance from the highway increased at the near-road site, we observed decreases in rBC mass and number concentrations and increases in the number fraction of rBC particles with thick coatings (f). The latter likely occurred due to rapid processing of the highway plume and entrainment of urban background particles. Most rBC-containing particles measured near the highway were either uncoated or thinly coated. In Redlands, we found that rBC mass concentrations on weekdays were similar to those observed at the furthest measured distance from the highway (114&thinsp;m). However, rBC number concentrations for the smallest measured sizes were an order of magnitude lower in Redlands than all measured distances from the highway. Observations of f indicate that values in Redlands during periods when estimated photochemical age (PCA) was highest (6–8&thinsp;h) were similar to corresponding values at the furthest measured distance from the highway. This suggests that the residence time of air in the Los Angeles Basin under typical summertime conditions measured during this campaign may not be sufficient for rBC to acquire thick coatings. However, under certain meteorological conditions, f was observed to be  ∼ 0.20 in Redlands, with coating thickness histograms showing a larger contribution of rBC particles with coating thickness  &gt; &thinsp;80&thinsp;nm. This occurred during a weekend day when local emissions from diesel vehicles were lower (compared to weekdays) and winds brought air from the desert regions to Redlands, both of which would increase the relative contribution of remote sources of rBC. Afternoon values of f (and O3) were found to be systematically higher on weekends than weekdays, suggesting that the weekend effect can create more thickly coated rBC particles presumably due to enhanced secondary organic aerosol (SOA) and reduced available rBC as condensation sites.</p