热-机械载荷下表面喷丸2A12铝合金残余应力松弛特性

Residual stress relaxation of shot peening 2A12 Al alloy under thermo-mechanical loadings

对2A12铝合金试样引入表面喷丸强化工艺,并进行热-机械载荷下的应力松弛试验,讨论喷丸残余应力场的演化特性。结果表明,喷丸强化可在试件表层引入合理的残余应力场,但在外部热-机械载荷下极易发生应力松弛。在短时、低周大应力加载条件下,循环应力将引起表面残余应力值与应力峰值大幅松弛;而在中、长时热-机械载荷下,热载荷成为恶化残余应力场的主要因素,各向同性材料沿各个方向发生趋势与程度一致的热应力松弛现象,机械载荷仅主要在其作用方向上加剧应力松弛。另外,纵、横向残余应力场演化趋势相同、程度不一,受热载荷或机械应力载荷的影响机制不同。

Several shot-peening processes and the stress relaxation experiments under ther- momechanical loadings were carried out on 2A12 A1 alloy specimens ,and then the evolutions of the shot-peened residual stress field was measured and analyzed. The results show that shot-peening processes can introduce reasonable surface residual stress field to the speci- mens, but the field would easily become relaxed under external thermo-mechanical loadings. Generally speaking, surface residual stress and peak stress would be relaxed a lot by the cy- clic stress under short-time, low-cycle and large stress loadings, while the thermal loads be- come the key factor in deteriorating the introduced stress field under long-time thermome- chanical loadings. Thermal stress relaxation occurs equally along each direction because of material isotropic homogeneity ,while mechanical loads only aggravate stress relaxation along its applied direction. Moreover, the evolutions of residual stress field present the same trend yet different degree along longitudinal and transverse directions, since the influence mecha- nism of thermal loadings differs from that of mechanical loads.