孔洞缺陷对3D打印Ti-6Al-4V合金疲劳试样应力分布的影响

3D打印金属技术因其个性化及可用于加工复杂零件等显著优点,在医用骨植入体领域得到了快速发展,但3D打印金属材料的孔洞缺陷所引起的应力集中现象严重降低了其疲劳强度,限制了3D打印生物金属材料的运用。本文针对3D打印Ti-6Al-4V合金超声疲劳试样,分析了Micro CT扫描试样得到的三维图像,获得了试样内孔洞缺陷的数量与体积;选择体积分数占比最大的孔洞,采用有限元方法分析了三种不同孔洞分布形式下的局部应力集中现象。研究发现,因空间位置的不同,独立的孔洞、接近自由表面的孔洞、相邻的孔洞三种不同孔洞的分布情况的应力集中系数差异显著。研究结果在一定程度上解释了目前EBM技术打印Ti-6Al-4V合金的孔洞缺陷如何对材料受力后的局部应力情况产生影响。

On the Effect of Void Defects on Stress Distribution of Ti-6Al-4V Alloy Fatigue Specimen in 3D Printing

3D printing metal technology has been developed rapidly in the field of medical bone implants due to its unique characteristics,which and can be applied in complex part machining.However,the stress concentration phenomenon caused by void defects in 3D printing metal material has seriously reduces its fatigue strength,which limits the application of 3D printing biological metal materials.In this paper,aiming at the printing of Ti-6Al-4V alloy ultrasonic fatigue specimen,analyzing the 3D images from Micro CT scanning,the number and volume of voids in specimen were obtained.Selecting the void which has largest volume fraction,local stress concentration in three kinds of void distribution form was analyzed by using finite element method.Study reveals that due to the difference of spacial location,stress concentration coefficients are significantly different for three distribution forms:single void,void close to free surface and adjacent voids.Above results may explain,at certain degree,how the void defect in current 3D EBM printing Ti-6Al-4V alloy is affected by local stress in material subjected to loading.