Preparation And Mechanical Properties Of Self-reinforced Polyethylene Composites

Ultra-high molecular weight polyethylene (UHMWPE) fibers have excellent integrated properties. Their materials are relatively inexpensive and source broad. Flotsam can be reclaimed. Moreover, UHMWPE fibers as reinforcing materials have above properties, so they play an important role in region of composites. In this study orthogonal experimental design was utilized, optimum processing conditions of UHMWPE/PE laminates were obtained. Fibers content is one of important factors that affect tensile strength and shear strength in structural design of UHMWPE/PE laminates. Temperature is a most important factor among all processing parameters in this research. Rising temperature is useful for enhancing interfacial strength, but it can affect the strength of UHMWPE fibers. The effects of duration and pressure on are relatively small. So good integrated properties of UHMWPE/PE laminates can be achieved, if low temperature and long duration of processing conditions are used.In order to optimize the designs and evaluate exactly the performances of UHMWPE/PE laminated composites, it is necessary to study the damage mechanisms of these materials, and to indicate the rules of the damage propagation, then to predict the effects of what on the various performances such as stiffness, strength and so on with the damage developing. In the research about the mechanical problems of composite materials, numerical models used in the conventional simulations can be classified into the following three types. Firstly, any cross section of the laminated composite is modeled by using plane-strain elements. However, the mechanical behavior of the laminated composite always has the complex three-dimensional deformations. Therefore two-dimensional simulation using plane-strain elements are not adequate. Secondly, the laminated composite is sometimes assumed to be a single equivalent stiffness plate by means of classical lamination theory, and modeled by using shell elements. This method cannot simulate the in-layer fracture and the interlaminar delamination separately. Thirdly, the laminated composite is modeled by using three-dimensional solid elements. Obviously, in order toobtain the effective results of numerical calculation, the mesh must be very fine and material having certain periodicity is required, so the calculating amount is quite huge. With increasing loading, the multiple damage modes which are interfacial fracture between the fiber and matrix, the matrix cracking and interlaminar delamination etc. in the laminated composites may be occurred. When this damage process is simulated by using finite element numerical method, elements must be remeshed and iteratively calculated to any change of the microstructure, until the structure evolves and tends towards stability. Then, the same simulation step is carried out with further increasing the loading. Such simulating process requires the computer is great in capacity and the computer working time is very long. Accordingly, it cannot usually be afforded to spend that numerically simulating the damage processes of true multi-layer of laminated composites. Based on the quasi-3-demensional model concept, unreasonable aspect associated with fibers area modeling of Nishiwaki's model was modified, and the numerical model of UHMWPE/PE laminated composites was proposed in this paper. The damage propagation processes of UHMWPE/PE laminated composites subjected to tensile loading were investigated and different fractural phenomena such as the transverse crack and interlaminar delamination etc. in the composite laminates were simulated at the same time by using aforementioned modified numerical model. The damage mechanisms were revealed, the effects of ply stacking angles and sequences on were discussed and the strengths were predicted for those materials. Tensile stress-strain curves of experimental data were consistent with those of the numerical simulating for aforementioned laminated composites. The levels of tensile stresses that correspond to transverse crack, interlaminar delamination and their propagation can be predicted. Though stacking sequences of layers of above UHMWPE/HDPE quasi-isotropic laminates are different, sequences of initial cracking of their single ply are same, namely, first to be 90° layer. The damage initiation and propagation correlate with ply stacking angles and sequences of UHMWPE/HDPE quasi-isotropic laminates.In order to verify further this modified finite element mechanical model, next studies are that correlative experiments will be performed by means of acoustic emission technology etc. The damage mechanisms of self-reinforced polyethylene composites laminates (UHMWPE/HDPE) being subjected to tensile loading were investigated by acoustic emission technique and a scanningelectron microscope technique in this study. The correlations were established between the dominant failure mechanisms and acoustic emission events amplitude for model specimens which exhibited the dominant damage mechanisms. Results revealed that fiber-matrix interfacial debonding, matrix plastic deformation and cracking, fiber pull-out, fiber breakage and interlaminar delamination are associated with acoustic emission events having amplitude range 30 dB to 45 dB (low amplitude events), 30 dB to 60 dB (low amplitude events), 60 dB to 80 dB (middle amplitude events), 80 dB to 97 dB (high amplitude events) and 60 dB to 85 dB (middle amplitude events), respectively. These correlations can be used to monitor the damage growth processes in the UHMWPE/HDPE composite laminates exhibiting multiple modes of damage, to evaluate the structure integrality and predict the life of these materials. Results from this study revealed that the acoustic emission technique is a viable and effective tool for identifying the damage mechanisms in the UHMWPE/HDPE composite materials.Using the correlations established between the types of damage in the UHMWPE/HDPE laminates and the acoustic emission results in terms of the events amplitude, measuring and analyzing amplitudes of acoustic emission signals were performed for different types of UHMWPE/HDPE quasi-isotropic laminates under the tensile loading conditions. Accumulative numbers of acoustic emission events for [0/90/45/-45]s (type A), [0/45/-45/90]s(type B), [45/-45/0/90]s(type C) specimens of UHMWPE/HDPE quasi-isotropic laminates vs tensile stress curves are different each other, corresponding loading levels of their same type of damage occurred are not equal. Results revealed that ply stacking angles and sequences of UHMWPE/HDPE quasi-isotropic laminates affect the damage growth processes of these laminates. The acoustic emission characteristics of damage growth processes and the fracture mechanisms in those laminates were revealed. The validity of the finite element mechanical model established in this study was proved.