Abstract
The damage and fracture of fiber reinforced polymer composites are vital constraints in their applications. To understand the mechanism of damage of wood fiber (WF) reinforced high density polyethylene (HDPE) composites, we used waste WF and recycled HDPE (Re-HDPE) as the raw materials and prepared high-filled WF/Re-HDPE composites via extrusion. The damage and fracture mode and failure mechanism of the composites with different WF contents (50%, 60%, and 70%) was studied under a three-point bending test by combining the acoustic emission (AE) technique and scanning electron microscope (SEM) analysis. The results show that AE technology can better assist in understanding the progress of damage and fracture process of WF/Re-HDPE composites, and determine the damage degree, damage accumulation, and damage mode. The damage and fracture process of the composites presents three main stages: the appearance of initial damage, damage accumulation, and destructive damage to fracture. The matrix deformation, fiber breakage, interface delamination, fiber-matrix debonding, fiber pull-out, and matrix cracking were the dominant modes for the damage of high-filled WF/Re-HDPE composites under bending load, and the AE signal changed in different damage stages and damage modes. In addition, the WF content and repeated loading had a significant influence on the composite’s damage and fracture. The 50% and 60% WF/Re-HDPE composites produced irreversible damage when repeated load exceeded 75% of the maximum load, while 25% of the maximum load could cause irreversible damage for 70% WF/Re-HDPE composites. The damage was accumulated owing to repeated loading and the mechanical properties of the composites were seriously affected.
Highlights
Natural fiber composites depend on their inherent environmental and performance advantages and have become an alternative for replacing environmentally harmful synthetic materials, and help control pollution problems [1]
The bending procedure of high-filled wood fiber (WF)/Re-high density polyethylene (HDPE) composites consisted of three steps: line elastic deformation, nonlinearity deformation, and fracture
The bending procedure of high-filled WF/recycled HDPE (Re-HDPE) composites consisted of three steps: bending test
Summary
Natural fiber composites depend on their inherent environmental and performance advantages and have become an alternative for replacing environmentally harmful synthetic materials, and help control pollution problems [1]. Polymers 2019, 11, 170 the WF/HDPE composites and expands, causing larger cracks or even breakage under sustained loading, resulting in material scrapping or life reduction. The damage and failure modes of fiber reinforced polymer composites are mainly divided into fiber pull-out, fiber breakage and delamination, matrix cracking, and fiber-matrix debonding [5,6,7,8,9]. It has been difficult to accurately and effectively distinguish the failure modes and understand the evolution of the damage mechanism of high-filled WF/HDPE by using the traditional evaluation methods and testing techniques. AE is one of the most reliable and well-established novel techniques in non-destructive testing, which can monitor and identify the stress wave signals of the composite from the microscopic deformation stage until the fracture process. The accumulation of damage during the deformation and failure process is monitored, the failure mechanism is identified, and the damage location and fracture modes are determined [10,11,12,13,14]
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