Effect of process parameters on mode-II interlaminar fracture toughness and fractographic features of automated fibre placement prepreg laminates

The present study concerns the quantitive assessment of the influence of process parameters on the interlaminar properties of carbon fiber reinforced epoxy composites. Mode II interlaminar fracture toughness is evaluated based on the ENF test. Scanning electron microscopy images are used to evaluate the change in microstructures. The results indicate that the process parameters have a direct influence on the microstructural features and fracture toughness of laminates. Specifically, the elevation of layup speed leads to the increase of interlaminar porosity which results in a decline of fracture toughness. The moderate pressure could sufficiently evacuate air bubbles during the deposition which to a certain extent decreases the porosity; however, the excessive pressure squeezes resin out from the interlaminar region, which decreases the fracture toughness. Furthermore, the excessive temperature could both increase porosity and result in a thinner resin layer due to the change in resin flowability. In which case, the fracture toughness would be significantly decreased.

Анализ усталостного разрушения рельсовой стали

In present paper attempt was made to find a relationship between the mechanical properties of the material in microvolumes and the properties of the material under load. A fractograph-ic analysis of the surface of the fatigued scrap rail with the inner transverse crack is given. The relationship between the fractographic features and the structure of the material is dis-cussed. A sample with an internal transverse crack in the head of the rail was removed from service after an intense cyclical load in the railway switch. For metallographic research, the sample was subjected to three-point bending. On the surface of the destruction of the rail re-vealed three areas, differing in the degree of brittleness of the material.

Role of Zirconia Filler on Mechanical Properties of HDPE/UHMWPE Blend Composites

Hybrid composites based on high-density polyethylene-grafted maleic anhydride /ultra-high density HYPERLINK "https://www.sciencedirect.com/topics/materials-science/polypropylene" \o "Learn more about Polypropylene" polyethylene (HDPE/UHMWPE) loaded with short glass fiber (SGF) and zirconia (ZrO2) micron sized particles were fabricated by melt-mixing process and their physical and mechanical properties were determined. Physio-mechanical properties such as density, hardness, flexural properties and impact strength of these composites were studied. The presence of SGF and ZrO2 in the grafted HDPE/UHMWPE blend increased the hardness, bending strength and modulus. However, impact strength decreased with increase in ZrO2 loading. Further, it was found that the HDPE/UHMWPE blend with 25 wt. % SGF and 2.5 wt. %ZrO2 showed optimum mechanical properties due to improved fiber/matrix adhesion. Scanning electron microscope was used to identify the fractographic features of the selected fractured coupons.

Strengthening Al-Zn-Mg Alloys via Ultra-Fine Lamella Structures Containing a High Density of Dislocations and Clusters

A new method of thermo-mechanical processing has been designed by introducing pre-aging before general cold rolling for an Al-Zn-Mg alloy. This process results in an increase of 200 MPa in yield strength compared to that of the peak-aged samples. The microstructures were examined by transmission electron microscope and X-ray diffraction. It has been found that the enhanced strength is mainly contributed to by ultra-fine lamella structures containing a high density of dislocations pinned by nanoprecipitates. Extra strength is provided by the “interlocking” of precipitates and dislocations. Fractographic features analysis shows that crack propagation along the interface of the lamella structures is the direct reason for resulting in fracture, due to intra-granular strength exceeding grain boundary cohesion.