Search

• The dynamic response and damage modes of UHMWPE laminates under two-point asynchronous impact were investigated. • The area of delamination damage under the first and second impacts was quantified. • The reason for the higher ballistic limit at second impact at 2 cm impact spacing is revealed. • The energy absorption mechanism and delamination damage weights at the second impact are revealed. The impact from multiple bullets leads to more severe damage to fiber composite laminates, and the dynamic response becomes more complex. However, current research has focused on studying the ballistic limit and single impact response of materials. In this study, an experimental method to investigate the dynamic response and damage modes of fiber composite materials under multi-point asynchronous impacts is proposed. The aim is to reveal the mechanisms behind the differences in ballistic limits and energy absorption of UHMWPE (Ultra-High Molecular Weight Polyethylene) fiber composite panels at different impact distances. Through CT scanning and DIC (Digital Image Correlation) techniques, the delamination area and dynamic response of the laminates were quantitatively analyzed. The results show that the ballistic limit of the second impact is increased by 3.05 % when the impact distance is 2.5 times the diameter of the bullet. The maximum difference of energy absorption compared to the first impact was only 3.7 % at an impact spacing of 5 times the diameter of the bullet, despite the interference in the damage region. From the perspective of energy absorption, the two impacts are independent. Multiple impact tests are critical for protective materials, and the results of this study provide important insights into UHMWPE fiber laminates in terms of multi-point impact. [ABSTRACT FROM AUTHOR]

• The UHMWPE fabric was modified by plasma treatment and polypyrrole grafting. • Low-velocity impact and residual compressive tests were conducted. • X-ray micro-computed tomography was used to quantify the microscopic void distribution. • Combined plasma treatment and polypyrrole grafting could improve the impact resistance. The physical–chemical method with plasma treatment and polypyrrole grafting was used to improve the low velocity impact resistance of the ultra-high molecular weight polyethylene (UHMWPE) fiber/epoxy laminates. The experimental impact force–time curves and impact force-central displacement curves were recorded. The microscopic void distribution of impact region was quantitatively counted by high-resolution X-ray micro-computed tomography (μCT). Then the residual compressive strengths for the laminates after low velocity impact were explored. Experimental results showed that the impact resistance and residual strength of the laminates treated by the combined plasma treatment and polypyrrole grafting were significantly improved by comparing with the plasma treatment alone, and the void fraction also reduced remarkably. In addition, the impact resistance with single physical plasma treatment method was more affected by the mixture ratio of nitrogen and oxygen. [ABSTRACT FROM AUTHOR]