Damage accumulation near the cold-expanded hole due to high-cycle fatigue by crack compliance method

The novel destructive method is implemented for quantitative assessment of fatigue damage accumulation in the stress concentration zone accompanied by residual stress due to cold expansion of the through-thickness hole. Damage accumulation is reached by preliminary cyclic loading of plane specimens with cold-expanded holes. Narrow notches, emanating from the hole edge at different stages of high-cycle fatigue, serve to manifest a damage level. These notches are inserted without applying external load. Deformation response to local material removing, caused by pure residual stress influence, is measured by electronic speckle pattern interferometry (ESPI) in terms of in-plane displacement components. Normalized values of the notch mouth open displacement (NMOD), in-plane displacement component at the initial point of the notch acting in the notch direction (U0), in-plane displacement component at the final point of the notch acting in the notch direction (U1) and the stress intensity factor (SIF) are used as current damage indicators. Numerical integration of curves, describing an evolution of each fracture mechanics parameter over lifetime, produces the damage accumulation function in an explicit form. It is established that all four fracture mechanics parameters give very close results.

Analytical studies on Mode III fracture in flexoelectric solids

Due to the stress concentration near crack tips, strong flexoelectric effect would be observed there, which might lead to new applications of flexoelectricity in material science and devices. However, different from the flexoelectric effect in cantilever beams or truncated pyramids, at the crack tip, multiple components of strain gradients with nonuniform distribution contribute to the flexoelectric effect, which makes the problem extremely complex. In this paper, with the consideration of both direct and converse flexoelectricity, the electromechanical coupling effect around the tip of a Mode III crack is studied analytically. Based on the Williams' expansion method, the displacement field, polarization field, strain gradient field along with the actual physical stresses field are solved. A path independent J-integral for Mode III cracks in flexoelectric solids is presented. Our results indicate that the existence of flexoelectricity leads to a decrease of both the J-integral and the out-of-plane displacement in Mode III cracks, which means that the flexoelectric effect around the tip of Mode III cracks enhances the local strength of materials.

Numerical Assessment of a Sustainable Blast Protection Wall

Terrorist attacks have increased in the past few years in different countries. Explosions are problem that has significant impact on human life, as well as the social and economic situations. Engineers have designed targeted structures to mitigate blast effects. However, design blast-resistant systems is pricey and not suitable choice in most cases. Therefore, install blast barriers to protect occupants and instructed can reduce casualties and losses. Most current studies have investigated the performance of multi-layer composite blast barriers composed of advanced materials, which is not only costly, but require skilled labour to construct. The present study conducts numerical analysis of eco-friendly composite blast protection wall to mitigate blast. The wall structure consists of two face-sheet of adobe brick and core layer of crushed recycled aggregate. The analysis framework includes three different blast wall models using ABAQUS®. The explosive charge of 1-kilogram TNT is placed at different standoff distances from 0.25 to 4.0 meter in front of the wall. The authors conclude sustainable materials to design blast barriers could be effective in reducing the intensity of explosions in certain blast scenarios. The thickness of the core layer and standoff distance have the main contribution to identify the blast response of the blast wall. For instance, the calculated out-of-plane displacement results showed when 1- kg TNT place at 0.5-m from the wall, and thickness of the core increases from 30-cm to 60-cm, the displacement decreases by 38.74%. While the acceleration decreases by 75% for the same range of increase of thickness of the core layer. The present study calls researchers to investigate the performance of low-cost, and environment-friendly materials to attenuate abnormal loads wether are man-made or natural hazards.

The Staircase Drive—A Novel Actuator Design Optimised for Daisy-Chaining and Minimum Stress Load Coupling

This work presents a novel type of actuator that improves over the standard cantilever by permitting daisy-chaining while minimising stress to the joint connecting to the load. A detailed structural and functional comparison of the proposed device against the cantilever actuator as a baseline is given, led by a brief revision of the cantilever actuator as the state-of-the-art that highlights its limitations with respect to daisy-chaining and the stress it inherently creates within the joint connecting to the load when attempting out-of-plane displacement without rotation. Simulations of both devices’ performance confirm that the newly proposed device yields the targeted displacement profile that both enables the daisy-chaining of such a device into a higher-order actuator for increased displacement and reduce stress in the joint with the load. This comes at the cost of reduced maximum displacement compared to the cantilever, which can be overcome by daisy-chaining. The proposed device’s performance is further evaluated on the basis of manufactured prototypes measured by means of a laser scanning vibrometer. The prototype was manufactured on a 150m alumina substrate, and both electrodes and piezoelectric layer were deposited in a thick-film printing process.

Application of 3D vision intelligent calibration and imaging technology for industrial robots

During modern flexible lean manufacturing, flexible operation of irregular and complex workpieces with different specifications and arbitrary placement is an essential ability of industrial robots, while it cannot be met by traditional clamping methods. Vision technology brings flexibility and convenience to industrial robots, but the common two-dimensional technology only involves three degrees of freedom (plane displacement and rotation), which hinders the positioning of arbitrarily placing workpieces (often six degrees of freedom) and disorderly sorting. In addition, for typical visual tasks in industrial environments like defect detection, accurate distinguishing of such defects as pits and scratches is challenging under two-dimensional plane imaging. The introduction of three-dimensional information provides an effective solution to this problem. Thus, in the face of increasingly complex, flexible, intelligent and personalized manufacturing needs, the acquisition and processing of 3D visual information are of much importance.