Neural network with Particle Swarm Optimisation for Analysing Band Structure of Elastic Metamaterials

Background: Due to the development of computing resources, machine learning techniques and models integrated with evolutionary algorithms have been successfully applied to solve a vast of engineering problems. With the advance in elastic metamaterial research, the identification of band structure, which reflects the physical property of Elastic Metamaterial, holds the key to the design of wave-controlled devices. Objective: In order to conduct bandgap analysis on two specific metamaterial structures, machine learning models that are integrated with the evolutionary algorithm are proposed to predict band structure. Methods: This paper proposes two integration models with a modified loss function for predicting elastic metamaterial’s band structure. The self-defined loss function composed of mean square error and concordance correlation is designed to ensure the numerical eigenfrequency values but also the position of each band. Results: The results of the integration models indicate the MLPs-PSO and RBFs – PSO models indeed have relatively satisfying performances on such pattern recognition tasks with respect to the numerical values of the error measurements. The performances of the machine learning models could be outstandingly improved by the Particle Swarm Optimisation algorithm. Conclusion: In short, the well-trained machine models are able to predict the band structure and could be contributing to bandgap enlargement study.

A non-iterative inverse method for the identification of time and space-dependent heat sources of multi-dimensional FGMs by boundary temperature data

Background: Detection of heat sources is frequently encountered in many fields of science and engineering and plays a significant role in monitoring and control of many engineering thermal systems. Objective: The objective of this paper is to estimate the space and time-dependent heat sources in multi-dimensional functionally graded materials using boundary temperature data. Methods: First, the dimensionless temperature at the measurement points on the boundary is obtained by a direct process. Then, the objective function is obtained by a series of matrix operations, and the relationship between the temperature at the measurement points and the unknown parameters is established. After that, the strength of the heat sources can be inversed directly by the least-square error method, then the location and number of the heat sources can be obtained directly from the strength distribution of heat sources. The coefficient expansion method and truncated singular value decomposition method are applied to reduce the ill-posed degree of the inverse process. Results: Through the analysis of typical 2-dimensional and 3-dimensional examples, the influence of various factors such as the type of basis functions, the circular supported radius and the measurement noise on the inversion results is discussed, which shows that this method can identify the strength, location and number of heat sources of FGMs well. Conclusion: A non-iterative inverse method based on precise integration finite element method and least-square error method is established to estimate the strength, location and number of the unknown heat sources of functionally graded materials using boundary temperature data.

Elastic Guided Waves in Bistable Composite Structures – Experimental and Numerical Investigation

Background: Bistable composite laminates are emerging as smart structures in automotive and aerospace applications. However, the behavior of the wave propagation within such laminates has not been investigated, which hinders their implementation in structural health monitoring (SHM) and non-destructive evaluation (NDE). Objective: As a result, this manuscript examines the propagation behavior of guided waves in bistable composite structures. By understanding the effect of pre-stressing in bistable composite laminates on the characteristics of propagating waves, such as velocity and amplitude, a more knowledgeable decision about their applications in flaw detection and assessment can be made. Methods: The fundamental symmetric (S0) and anti-symmetric (A0) Lamb wave modes were investigated during propagation in two bistable composite laminates, [0/90]T and [02/902]T, and were assessed experimentally and numerically using ABAQUS. For the tested frequencies, which ranged from 60 kHz to 250 kHz, the behavior of the propagating wave was evaluated for both stable configurations and across two different actuators that were lined up with the fiber directions. Signal processing techniques were thus extensively used to enhance the measured signals and identify both the group velocities and the amplitudes’ trend of the S0 and A0 wave modes. Results: Our results showed that there is a minimal variation (typically below 1%) in the amplitude and velocity of the A0 and S0 modes when the composite plates switch between the first stable configuration and the second stable configuration in both composite plates. These results were numerically validated by replicating the bi-stability of the composites. The numerical data were in relatively close agreement (10% average error) with the experimental values and trends. Furthermore, the bistable effect was examined in detail relative to a reference numerical flat (monostable) plate. Although the bistable effect induced a notable amount of internal residual stress, this did not significantly impact the propagating wave modes, with a maximum difference of about 2% when comparing wave velocities. Conclusions: The effect on the wave propagation behavior along different directions of both stable configurations was shown to be minimal. These results, which were validated numerically, clear the ambiguity on the usage of these laminates in experimental health monitoring.

Mechanism of Inhibition of Hydroxyapatite Nanoparticles on Cancer Cells and Recent Advances in the Field

Background: Calcium phosphates are chemically similar to bone minerals. The biocompatibility, bioactivity, and high similarity of these substances to body organs such as bone have made them a good choice for disease diagnosis and treatment. Here, the main use of calcium phosphates is diagnosis and treatment of cancers. Hydroxyapatite is a bioactive material with a high affinity for DNA and protein. Recently, hydroxyapatite nanoparticles exhibit different properties than those of bulk hydroxyapatite in chemistry and biology. In general, the anticancer effects of hydroxyapatite nanoparticles have been attributed to high amounts of endocytosis in cancer cells and inhibits of protein synthesis in cells. Methods: Herein, we evaluated the structure, properties, and methods of synthesis of hydroxyapatite nanoparticles. Moreover, the mechanism of inhibition of hydroxyapatite nanoparticles on cancer cells and recent advances in this field have been examined. Conclusion: Hydroxyapatite nanoparticles had the ability to eliminate the development of cancer cells in vitro and in vivo. In the live tissue environment, injection of hydroxyapatite nanoparticles at the tumor’s surrounding area had a significant decrease in tumor size (about 50%).

Optimization of Die design to abolish surface defect on Telescopic Front Fork (TFF) Tube

Background: The telescopic fork is mainly used for suspension purposes in the different devices to absorb the vibration and disturbances from the road or mechanical devices. Factors such as die angle, drawing velocity, lubrication, and area reduction per pass significantly affect the drawing loads and residual stresses formed in the drawn tube during the tube marking process. Objective: Instantaneous transverse crack was found on the pipe's outer surface during the drawing process in the current work, and the key challenges were to reduce the percentage of pipe rejection. Methodology: In this work, optimum drawing die designs were proposed by using the finite element method (FEM). A FEM solving tool called Abaqus has been used for simulating and solving the cold-rolled process. The FEM model of the cold drawing process is generated in Abaqus with the same boundary condition (Axial load and constrain) as using on the actual wire drawing machine. Result: There was a substantial reduction in the area; axial stress (Tensile) along the die side is 672 MPa which is 23 % lower than the current die axial stress value of 877 MPa. A 48 % plastic strain was found along the purposed die side, which was 17 % lower than the existing strain of 64%. Finally, reduced the area by changing the die geometry from ~52% to 35 to 40 %. Conclusion: It was possible to abolish transverse crack on the pipe's outer surface to reduce the area reduction (35 to 40 %) in the output tube and strain (17 %). As part of the optimization of the FEM work process, this work gives us encouraging results. Further research will be considered for future positions.

Nanoscale Reciprocating Sliding Contact Behaviors of an Isosceles Trapezoid Textured Surface in Space Environment

Background: In space environment, microgravity and vacuum influence the mechanical behaviors of the devices. In microgravity environment, the mechanical components will vibrate with a small amplitude once there is a disturbance. The vibration can be seen as a reciprocating sliding contact with a small amplitude. In addition to the vibration, adhesion effects are predominant in vacuum, which will induce a high friction force. Objective: To reduce the friction force, textured surfaces are widely used in mechanical engineering on the earth, and nanoscale textures are also verified that they can be used to improve the frictional behaviors of components with the size of nanometers. Methods: In this paper, the adhesion effects are considered by using molecular dynamics (MD) simulation, and the microgravity induced vibration is simplified as a reciprocating sliding contact. Coupling MD simulation and the finite element method, a multiscale method is used to investigate the frictional properties of nanoscale reciprocating sliding contact between rigid multi-asperity tips and an isosceles trapezoid textured surface. Results: Average friction forces for the different tips are presented, and the friction processes are analyzed. A stable friction process is discovered for a specific case, and the average friction forces keep at two stable values corresponding to two sliding directions. Conclusion: Compared with the total average friction forces of a smooth surface, the textured surface can reduce the friction forces greatly. This work could contribute to the textured surface design to improve frictional properties in space environment.