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.

基于熔融的材料挤出增材制造，通常称为熔融丝制造（Fused Filament Fabrication，FFF），是一种逐层制造工艺，可制备定制化构件，尤其擅长制造复杂几何结构，应用覆盖航空航天、汽车、医疗等诸多领域。鉴于这些行业的严苛属性，亟需厘清受试增材制造（Additive Manufacturing，AM）材料、所产生损伤的特性，以及这两类参数对构件未来服役性能的影响。本研究旨在探究常用功能性FFF材料的低速冲击与所产生损伤之间的关联，并开发基于超声无损检测（Ultrasonic Nondestructive Evaluation，UT）的损伤可视化方法。本研究采用Essentium HSE打印机制备了两类试样：分别为纯尼龙原料，以及掺杂10%短切碳纤维的尼龙原料，并在不同冲击能量下开展冲击试验。通过超声检测（UT）对损伤范围进行可视化表征，观测到了显著的内部开裂现象。采用四点弯曲试验，对比了材料在未受冲击状态、3J低冲击能量冲击后，以及7J高冲击能量（会导致可见断裂）冲击后的力学行为。此外，还对两个试样开展了X射线计算机断层扫描（X-ray CT）试验，以验证超声检测的结果。