外文翻译-显微硬度表征板材成形过程中的实验特性的应用.doc

1、Experimental characterisation in sheet forming processes by using Vickers micro-hardness techniqueAli Mkaddem, Riadh Bahloul, Philippe Dal Santo, Alain PotironLPMI-ERT-ENSAM/CER, 2 Boulevard du Ronceray,BP3525-49035 Angers, FranceReceived 23 April 2004; accepted 10 April 2006AbstractIn this paper, a

2、n experimental micro-hardness procedure is proposed to evaluate the evolution of HSLA steel behaviour during each sequence of sheet forming process. As micro-hardness technique offers a reliable inspection, it was retained here to follow the mechanical characteristic changes, which may happen during

3、 manufacturing progress. This contribution consists in characterisation of sheet material at different steps: virgin sheet, unreeled sheet, straightened sheet and bent sheet. Measurement performed on virgin HSLA steel showed that material is highly heterogeneous within the sheet thickness. The micro

4、-hardness profiles examined after the bobbing-off step showed a high sensitivity of sheet behaviour to straightening operation that is widely adopted in steel working in order to make sheet sufficiently flat for forming. A level of hardening ratio between virgin material and straightened material ha

5、s been clearly observed. Moreover, micro-hardness is investigated on bent parts at the fold zone for displaying the mechanical properties modifications under a large gradient deformation. In this way, hardening phenomenon and damage phenomenon, which are generally activated simultaneously for elasto

6、plastic steel, are quantified accurately. Results compared into them gave a good idea about the interaction of processmaterial during manufacturing. 2006 Published by Elsevier B.V.Keywords: Micro-hardness; Sheet metal; Bobbing; Straightening; Bending; Damage1. IntroductionSheet metal forming industr

7、y has become one of the major manufacturing centres of the automobile industry. The popularity of sheet metal products is attributable to their light-weight and their higher formability.Sheet working consists in a more complex plane straining process, designed with high ratio of thickness reductions

8、 involving a considerable amount of texture evolution as mentioned by Tang and Tai 1.Diversity of sheet metal manufacturing sequences as bobbing, bobbing-off, straightening and bending, as shown in Fig. 1, leads to a level and progressive change of material characteristics.At several time, mechanica

9、l and environmental conditions of forming are considered among the main causes that induce a decrease in steel strength designed with microstructure changes during forming cycle 2.Fig. 1. Main sequences for manufacturing cycle.- Corresponding author.E-mail address: ali.mkaddemangers.ensam.fr (A. Mka

10、ddem).0924-0136/$ see front matter 2006 Published by Elsevier B.V.doi:10.1016/j.jmatprotec.2006.04.006In pioneering studies 37, the main investigation of material strength, resistance to thinning, damage and ability of material to forming are extensively performed for one material state or for separ

11、ate steps.Indentation micro-hardness testing at low loads is a well-accepted tool for assessing various mechanical properties such as flow stress, fracture stress, Youngs modulus and fracture toughness of rolled material 8. Thus, a proposed method for measuring micro-hardness is used to follow the p

12、roperties variation with the evolving of manufacturing sequences of 0.09%HSLA sheet metal carbon steel. Curves deduced from the measured values within the sheet thickness are discussed for allconsidered steps of the forming processes.2. Rolling process2.1. Rolling cycleThe rolling process consists o

13、f several successive steps as shown in Fig. 2, which govern the final state of matrix material. The level of thickness reduction leads to a high-hardened metal by introducing an important change to the crystallographic texture 9.Fig. 2. Main steps for sheet rolling processes.In the general manufactu

14、ring practice, the holding temperature of the slab must be enough high to make once again the precipitations, formed at the end of coiling, in the austenitic solution. It must be controlled accurately in order to lead to good material properties.At the end of hot rolling step, the temperature would

15、also be adapted precisely to make certain the successful precipitation of as small a grain size as possible. During this sequence, it must be assured that the used temperature cannot conduce to a heterogeneous microstructure.After rolling, the sheet is cooled by soaking, and then bobbed. The grain s

16、ize of material microstructure depends strongly on the adopted cooling speed. The grain size is as small as the cooling speed is high.The bobbing step has a specific influence on the final mechanical and microstructure characteristics of rolled steels. The bobbing temperature consists in an own thermal treatment of reheating the sheet. It has a particula