【摘要】 使用紧凑拉伸(CT)试样,研究了挤压AZ31B镁合金圆棒三个方向的组织及疲劳裂纹扩展性能。结果表明,疲劳裂纹以穿晶为主的混合方式沿滑移带扩展。T-L方向裂纹呈直线扩展,扩展速率最高,T-R方向孪生和滑移协同塑性变形,裂纹局部偏转,呈波浪形沿径向扩展,扩展速率较低,强织构和不均匀组织引起L-T方向裂纹分叉和偏离,降低了裂纹尖端有效驱动应力强度因子幅,裂纹扩展速率最低,在疲劳裂纹扩展速率(da/dN)与应力强度因子幅(ΔK)的关系曲线上出现水平段。在ΔK较小时加载频率对裂纹扩展速率的影响不大,ΔK>3 MPa m时裂纹扩展速率随着加载频率的提高而减小。更多还原

【Abstract】 Fatigue crack growth(FCG) experiments were carried out using extruded AZ31B magnesium alloy bar.The pre-crack compact tension(CT) specimens were oriented in three different directions with respect to the extrusion direction.The experimental results reveal that the specimen orientation has a significant influence on the FCG rate and crack path.The FGC rate of the T-L specimen is the highest while the L-T specimen shows the lowest value.Typical macroscopic Mode I crack is developed in the TL and T-R specimens whereas a deviation from the Mode I crack path and branching occur in the L-T specimens.For the L-T specimens,a plateau of constant crack growth rate occurs at low stress intensity factor range(ΔK).Transgranular cracking is the major cracking mode.Slip induced cleavage dominates the transgranular cracking in the T-L and L-T specimens whereas both twin boundary cracking and slip induced cleavage exist in the T-R specimens.The FCG rate decreases with the increasing load frequency at ΔK>3 MPa(l/g)～(1/2)m.更多还原