轴向及内压复合作用下Zr-Sn-Nb/Zr-Nb合金的多轴棘轮效应研究

A Study on Multiaxial Ratcheting Behavior of Zr-Sn-Nb/Zr-Nb Alloys Under a Combined Axial Load and Internal Pressure

为了模拟锆合金包壳在发生反应性引入事故(RIA)时的多轴应力状态,对Zr-Sn-Nb/Zr-Nb合金进行了单轴对称循环试验以及在内压及轴向载荷复合作用下的多轴试验,研究了两种合金轴向/环向棘轮应变的累积特性与内压及轴向应力的相关性.单轴拉伸试验结果表明,Zr-Sn-Nb合金和Zr-Nb合金的弹性模量相近均为85 GPa,屈服强度大约均为490 MPa.单轴棘轮试验结果表明,Zr-Sn-Nb合金和Zr-Nb合金在较小应力幅值下,由于无法启动孪生-退孪生机制,Zr-Sn-Nb合金和Zr-Nb合金都处于安定状态.当轴向应力幅大于325 MPa时,孪生-退孪生机制启动,Zr-Sn-Nb合金和Zr-Nb合金的轴向棘轮应变都在正方向上快速增加.由于泊松效应,环向棘轮应变则在负方向上累积.多轴棘轮试验结果表明,在恒定内压和不同轴向应力幅值的循环作用下,Zr-Sn-Nb合金和Zr-Nb合金的环向棘轮应变随轴向应力幅值的增大而增大.当轴向应力幅值大于325 MPa时,轴向棘轮应变呈现先负向累积、后正向累积的特殊现象;同时环向棘轮应变也随应力幅值增大而增大.在相同轴向应力幅值和不同内压加载下,内压对轴向棘轮应变呈现抑制作用,并且随内压的增大,其抑制作用更为显著.同时,内压对环向棘轮应变有明显的促进作用,导致环向应变快速正向累积.在轴向力和内压加载条件相同的情况下,Zr-Sn-Nb合金的轴向和环向棘轮应变比Zr-Nb合金小,说明Zr-Sn-Nb合金包壳管抵抗棘轮变形的能力更强.

In order to simulate the multiaxial stress state of zirconium alloy cladding in the event of a reactivityinitiated accident(RIA),uniaxial symmetric cyclic tests and multiaxial tests under a combined internal pressure/axial cyclic load were carried out on Zr-Sn-Nb and Zr-Nb alloys the correlation between the accumulated characteristics of the axial/hoop ratcheting strain of the two zirconium alloys and the internal pressure and axial stress were investigated.The results of the uniaxial tensile tests showed that the elastic modulus of Zr-Sn-Nb and Zr-Nb alloys were about 85 GPa,and the tensile strengths were about 490MPa.Results of uniaxial ratcheting tests showed that,under small stress amplitude,Zr-Sn-Nb and Zr-Nb alloys were in a stable state since the twinning-detwinning mechanism could not be activated.When the stress amplitude was greater than 325 MPa,the twin-detwinning mechanism was activated,so that the axial ratcheting strains of the Zr-Sn-Nb and Zr-Nb alloys increased rapidly in the positive direction.The hoop ratcheting strains accumulated in the negative direction due to the Poisson effect.The multiaxial experimental results showed that under a combined constant pressure and different axial stress amplitudes,the hoop ratcheting strain of Zr-Sn-Nb and Zr-Nb alloys increased with increasing axial stress amplitude.When the axial stress amplitude was greater than 325 MPa,the axial ratcheting strain accumulated negatively in the initial stage,then accumulated positively,and the hoop ratcheting strains also increased with increasing stress amplitude.Under the same axial stress amplitude and varying internal pressures,the internal pressure significantly restrained the axial ratcheting strain,and the restrain effect was more significant with increasing internal pressure.At the same time,the internal pressure had an obvious promoting effect on the hoop ratcheting strain,resulting in its rapid positive accumulation.The axial and hoop ratcheting strain of the Zr-Sn-Nb alloy were smaller than those of the Zr-Nb alloy under the same axial stress and internal pressure,which indicated that the Zr-Sn-Nb alloy was more resistant to the ratcheting deformation than the Zr-Sn alloy.