Ultra high molecular weight polyethylene (UHMWPE) fibers, also known as ultra-high modulus polyethylene (UHMPE) fibers or extended chain polyethylene fibers (ECPE), are the third-generation high-strength high modulus fibers that emerged in the early 1990s. Its relative molecular weight ranges from 1 million to 6 million, and its molecular shape is a linear extended chain structure. Its orientation is close to 100%, and its strength is the highest among fibers today, with good mechanical properties. Performance comparison with other fibers. UHMWPE fibers also have excellent properties such as resistance to ultraviolet radiation, chemical corrosion, high specific energy absorption, low dielectric constant, high electromagnetic wave transmittance, low friction coefficient, and outstanding impact and cutting resistance. Therefore, UHMWPE fiber is an ideal material for making soft bulletproof suits, stab proof vests, lightweight bulletproof helmets, radar covers, bulletproof armor for cash carriers, helicopter bulletproof armor, ship and ocean going vessel cables, lightweight high-pressure containers, aerospace structural components, deep-sea wind and wave resistant cages, fishing nets, racing boats, sailboats, ski sleds, etc. Due to the excellent performance and enormous application potential of UHMWPE fibers, UHMWPE fibers and their composite materials have received widespread attention both domestically and internationally in recent years.
The axial compression performance of UHMWPE fiber reinforced composite materials is relatively low, and even after treatment, the axial compression strength of sK66/epoxy composite materials is only 54.4 MPa (sK66 is the trade name of UHMWPE fiber). When the sample is compressed to 70% of the ultimate load, plastic deformation begins to occur and gradually increases, leading to shear failure until the sample fails, but does not continue to open. The main mechanism of compression failure of such materials is the instability of UHMWPE fibers under compression and the detachment of the bending interface. In addition, the bending performance of UHMWPE fiber reinforced composite materials is also very low. For example, the highest bending strength of the treated SK66/epoxy composite material is only 150MPa, which is about 1/7 of the tensile strength. When the load-bearing capacity of the compressed part exceeds the compressive strength of SK66 fibers under bending moment, the fibers become unstable, leading to delamination; The tensile part is delaminated due to the detachment of fibers and resin. Failure layer by layer, ultimately resulting in ductile bending failure. Bending delamination is the main bending failure mechanism of this type of material. Xian Xingjuan and others further studied the fracture toughness and crack propagation of UHMWPE fiber reinforced composite materials,. They adopted a three-point bending loading method, with a single-sided notch on the sample, and the ratio of the notch length (a) to the sample width (w) was 0.3. The deformation and propagation of fracture cracks were observed and photographed using a telephoto microscope. Experiments have shown that LDPE matrix has higher fracture toughness than epoxy matrix, and therefore can absorb more energy. When the bending load of LDPE matrix reaches the critical value, the crack tip becomes passive, and the fibers detach and turn white near the shear area of the crack. If unidirectional UHMWPE fiber reinforced resin is used, cracks will appear perpendicular to the direction of the notch in the sample; By using I-shaped UHMWPE fiber orthogonal woven fabric to enhance resin, passivation may occur at the top of the notch in the sample, and the accumulated plastic deformation may cause micro cracks, becoming stress concentration points and leading to plastic failure.