膨胀管可靠性评价方法研究

Study on Reliability Evaluation Method of Expansion Pipe

膨胀率是描述膨胀管尺寸变化的重要参数,对胀后膨胀管力学性能以及可靠性有重要影响。分析了不同膨胀率条件下膨胀管残余应力以及抗外挤强度的变化规律,利用可靠性理论建立了膨胀管失效评价模型。结果表明:膨胀管胀后力学性能受到冷作硬化以及壁厚变化量双重影响,屈服强度随着膨胀率增加达到峰值后基本保持不变;不同膨胀率的膨胀管在膨胀过程中残余应力随轴向的分布情况大体相同,数值随膨胀率增加而变大,增长量逐渐减小;受到椭圆度、壁厚不均匀度以及残余应力等不确定因素影响,膨胀管抗外挤与抗内压强度服从正态分布规律,不同膨胀率条件的膨胀管失效概率不同。该研究为膨胀管强度安全系数的科学设计提供依据。

Expansion ratio is an important parameter to describe the size change of the expansion pipe, and it has important influence on the mechanical properties and reliability of the expansion pipe. The change law of the residual stress and the anti-extrusion strength of expansion pipe under different expansion ratio is analyzed, and the failure evaluation model of the expansion tube is es- tablished using the reliability theory. The results show that, the mechanical properties of the expansion tube are affected by cold hardening and the change of wall thickness, and with the increase of the expansion ratio, the yield strength of the expansion tube in- creases, and it basically remains unchanged after reaching to the peak value; in the expansion process, the axial distribution laws of the residual stress of the expansion tubes with different expansion ratio are basically the same, the residual stress increases but the increment gradually decreases with the increase of the expansion ratio; influenced by the uncertain factors such as ovality, the un- evenness of wall thickness and the residual stress, the anti-extrusion strength and the anti-internal-pressure strength of the expansion tube are all subject to the normal distribution, and the expansion pipe with different expansion ratio has different failure probability. This study can provide the basis for the scientific design of the expansion pipe strength safety factor.