Impact efficacy of sandwich structures with additively manufactured skins and elastomeric foam cores
Sean Eckstein, George Youssef
Abstract
Sandwich structures are ubiquitous in various applications due to their superior specific properties, attracting assiduous research under a broad range of loading conditions. Introducing additive manufacturing (3D printing) of composite skins and considering novel elastomeric core materials necessitate exploring the process-property interrelationship with emphasis on impact loading. Therefore, this research study aims to elucidate the impact efficacy of additively manufactured sandwich structures, hinging on 3D-printed skins using continuous carbon fiber polymer matrix composites. The 3D-printed skins are adhered to polyurea foam cores with superior impact efficacy and remarkable recoverability. One sample set was subjected to low-velocity impacts using an instrumented drop tower at 4.43 m/s, and another separate set was submitted to moderate-velocity impacts using a small-scale shock tube at 15 m/s. All mechanical testing was accompanied by high-speed digital image correlation (DIC) to elucidate the whole field kinematic variables. The specimens were impacted under various testing parameters, including the size of the hemispherical impactor, sample configuration, mounting plate configuration, and impact velocity, to probe their dynamic behavior. The impact and deformation characteristics, including force-time, axial strain-time, and dynamic and permanent back-surface displacement signatures, were deduced from a high-fidelity force sensor, high-speed and high-resolution DIC, and a laser displacement sensor, and thoroughly analyzed to understand the efficacy of the newly designed sandwich structures. Reconstructive optical microscopy revealed the damage and failure that the structures endured. Across all sample configurations and testing parameters, the structures yielded an energy absorption of ∼91% of the input impact energy, exemplifying impact mitigation capabilities ideal for protective sports gear and structural components in aerospace, automotive, and defense applications.