Effect of impact energy on residual stresses induced by hammer peening of 304L plates

Effect of impact energy on residual stresses induced by hammer peening of 304L plates

Residual stresses induced by welding may reach the yield strength of the material and decrease the life of the components by premature cracking. The hammer peening process has been used to improve the fatigue resistance in welded components, especially at the weld toe. it is expected that the powerful hammer peening process produces a deeper compressive layer than other currently used processes and thus a better improvement irk fatigue life for heavy welds. To better understand residual stress relaxation by hammer peening, this study evaluates the effect of each hammer blow on the residual stresses field under the treated surfaces. An impact machine was used for hammering and generating unitary impacts at the same location. 304L steel plates were tested under 10-impact with various energy levels. Both initial stress free plates and plates with residual stresses were tested. Strain gages were used for recording strains at the surface in the near field of the impact, whereas in-depth residual stresses at 8 mm from the impact center were measured using the hole-drilling technique. The micro-hardness profiles were also measured to evaluate the hardening affected zone of the hammer peening. It was found that in initial stress free plates, hammer peening introduces compressive residual stresses. in plates with initial tensile residual stresses, hammer peening either released them or turned them into compression. it was found that increasing energy improves the hammer peening efficiency and that the first three or four hammer blows were the most effective. it was also found that the extent of the hammer-peening induced compression was around 1 mm. Microscopic observations of samples from the tested plates did not reveal cracks on the treated surfaces. (C) 2008 Elsevier B.V. All rights reserved.

焊接产生的残余应力可能会达到材料的屈服强度，并因过早开裂而降低部件的使用寿命。锤击强化工艺已被用于提高焊接部件的抗疲劳性能，尤其是在焊趾处。预计强大的锤击强化工艺会比其他现有工艺产生更深的压缩层，从而更好地提高大型焊接件的疲劳寿命。为了更好地理解锤击强化对残余应力的松弛作用，本研究评估了每次锤击对处理表面下残余应力场的影响。使用一台冲击机在同一位置进行锤击并产生单一冲击。对304L钢板在不同能量水平下进行10次冲击试验。对初始无应力钢板和带有残余应力的钢板都进行了测试。应变片用于记录冲击近场表面的应变，而使用钻孔技术测量距冲击中心8毫米处的内部残余应力。还测量了显微硬度分布，以评估锤击强化的硬化影响区域。研究发现，在初始无应力的钢板中，锤击强化引入了压缩残余应力。在具有初始拉伸残余应力的钢板中，锤击强化要么释放了这些应力，要么将其转变为压缩应力。研究发现，增加能量可提高锤击强化效率，并且前三次或前四次锤击最为有效。还发现锤击强化产生的压缩范围约为1毫米。对受试钢板样本的微观观察未发现处理表面有裂纹。（C）2008爱思唯尔有限公司。保留所有权利。