Analysis and Identification of the Mechanism of Damage and Fracture of High-Filled Wood Fiber/Recycled High-Density Polyethylene Composites

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.

Acoustic Emission-Based Study to Characterize the Crack Initiation Point of Wood Fiber/HDPE Composites

“…AE provides a novel method for the determination of the critical load due to its unique sensitivity to defects, damage initiation and expansion, and the initiative and dynamics of detection. Our previous work has shown that the damage of the high-filled WPCs has three stages, namely, the first stage is matrix deformation (elastic deformation), the second stage is fiber breakage and debonding (crack initiation and propagation), and the third stage is increased fiber debonding and fiber pull out, until matrix cracking to fracture (breaking stage) [7]. Therefore, fiber breakage and debonding are the signs of crack initiation and propagation.…”

“…The materials used in this work were wood fiber/recycled high-density polyethylene (WF/Re-HDPE) composites with 50%, 60%, and 70% wood fiber (weight percent (wt %), recorded as 50% WF/Re-HDPE, 60% WF/Re-HDPE, and 70% WF/Re-HDPE, respectively). The specific formulation and preparation process can be found in our previous work [7]. The prepared composite sheet was processed into a single-edge-notch bending (SENB) toughness test piece using a precision push bench saw (CS70EB, Festool, Wendlingen, Germany).…”

“…As a reliable, non-destructive testing technology, acoustic emission (AE) has emerged with a wide range of applications in the field of damage detection and quality evaluation of materials. The technology can monitor and identify stress wave signals of the composites ranging from microscopic deformation to the fracture process, including the crack initiation, propagation, delamination, and fracture [5,6,7,8,9,10,11,12,13]. The AE activity and AE intensity can be utilized to characterize the kinetics of the delamination process in Mode I fracture toughness tests for fiber-reinforced polymer laminates and provide reliable information on the delamination onset at both the microscopic and macroscopic scales [10,14].…”

Glass fiber/polypropylene composites with potential of bone fracture fixation plates: Manufacturing process and mechanical characterization

“…Consequently, the stresses near the screw holes can initiate crack which may split the sample along the axial direction. Damage patterns identification clarified delamination, debonding, crack opening and fiber pullout as the major sources of damage [35]. These could be evidenced by the formation of micro void spaces within the composite.…”

Application of Physical Methods for the Detection of a Thermally Degraded Recycled Material in Plastic Parts Made of Polypropylene Copolymer

“…They focused on three phases, which were the onset of damage, the accumulation of damage, and destructive damage resulting in breakage. The three-point bending test technique and combined acoustic emission (AE) and scanning electron microscope (SEM) analysis were used [ 9 ].…”