Over the past decades, high entropy alloys (HEAs) have attracted continuously increasing research efforts because of their technological promise for structural applications and their scientific interest as a multi-component alloy exhibiting an overall random solid solution structure with high mixing entropy at high temperature. In this summary, we briefly review the recent studies focused on the structure and mechanical behavior of HEAs, covering the important issues from phase stability to elastic modulus, mechanical strength, hardness and fatigue resistance. Finally, we highlight a few key findings recently reported for HEAs and discuss the outstanding issues yet to be resolved.

Fracture phenomenon in orthotropic materials, generally associates with region called, “damaged zone” in crack tip vicinity. In quasi-brittle materials, this area is known as fracture process zone (FPZ). This area contains a multitude of microcracks, which cause difficulties in analytical process of the region. Also, energy waste in damaged zone can affect the material fracture properties. The characteristics of damaged zone should be considered to figure out the residual strength of composite materials. It also can help to predict the value or even the direction of crack growth of orthotropic materials. So far, several efforts have been made to determine the mechanical properties of this region, but none of them (due to the immense complexity of this region) can express the behavior of this region properly. Moreover, previous approach has not been verified by new experimental and numerical results, yet. In the present study, a new approach “damaged zone simulation (DZS)” is proposed based on the experimental and numerical data, for investigating the orthotropic damaged zone properties. Comparison with existing analytical data shows the capabilities of the presented approach.

Nano composite materials based on polymers are widely used in restoration martials like dental. Poly methyl methacrylate (PMMA) is one of the most used polymers as dental material. PMMA has disadvantages such as low flexural strength properties and impact strength. In this paper, the influences of additive aluminum oxide and hydroxyapatite nanoparticles on the mechanical and strength properties of PMMA (including flexural strength, impact strength, surface hardness and shrinkage behavior) is studied experimentally. For this purpose, nine standard mechanical testing samples of pure PMMA, PMMA/5HA and PMMA/10HA with various amounts of Nano aluminum oxide (3,6,8 wt.%) were prepared. The results showed that the mechanical properties of hybrid Nano-composites were significantly improved in comparison with the pure samples in a way that optimal Nano-composite with convenience flexural properties and impact strength is obtained. Moreover, the use of nanoparticles results in shrinkage reduction of hybrid Nano-composites in comparison with pure PMMA.