Nondestructive Evaluation and Residual Property Assessment of Impacted Nylon/carbon-Fiber Additively Manufactured FFF Components Using Four-Point Bend and Ultrasonic Testing

Fusion-based material extrusion additive manufacturing, commonly known as fused filament fabrication (FFF), is a layer-by-layer manufacturing process known for creating custom components, specializing in complex geometries, with applications in the aerospace, automotive, medical, as well as many other industries. Due to the critical nature of these industries, it is imperative to understand the relationship between the AM material in question, the nature of the resultant damage, and the impact of these two parameters on the future performance of the component. The purpose of this study is to investigate the relationship between low-velocity impact and the resultant damage in common functional FFF materials and to develop methods of visualizing that damage using ultrasonic nondestructive evaluation. Coupons of a nylon feedstock infused with and without 10% chopped carbon fiber were fabricated using an Essentium HSE printer and impacted at various energies. The extent of the damage was visualized using ultrasonic testing (UT), in which significant internal cracking was observed. Four-point bend testing was utilized to compare behavior of the material prior to impact at a lower impact energy (3J), and a higher impact energy causing visual fracture (7J). X-ray CT was also performed on two samples to validate UT findings.

基于熔融挤出的增材制造技术，通常称为熔融丝制造（Fused Filament Fabrication，以下简称FFF），是一种逐层制造工艺，可定制化制备构件，尤其擅长制造复杂几何结构，在航空航天、汽车、医疗及诸多其他行业均有应用。鉴于上述行业对产品性能的严苛要求，明晰所研究的增材制造材料、构件所受损伤特性，以及这两类因素对构件远期服役性能的影响，至关重要。本研究旨在探究常见功能性FFF材料在低速冲击下的损伤演化关系，并开发基于超声无损检测（Ultrasonic Nondestructive Evaluation）的损伤可视化方法。研究采用Essentium HSE型打印机，制备了添加10%短切碳纤维与未添加短切碳纤维的尼龙基材试样，并对其施加不同能量的冲击载荷。借助超声检测（Ultrasonic Testing，以下简称UT）对损伤范围进行可视化表征，观测到显著的内部裂纹。本研究通过四点弯曲试验，对比了试样冲击前的力学性能，以及经低冲击能量（3J）与引发可见断裂的高冲击能量（7J）冲击后的力学行为。此外，研究选取两个试样开展X射线计算机断层扫描（X-ray CT）试验，以验证UT的检测结果。