EFFECT OF Z-PINS’ DIAMETER,SPACING AND OVERLAP LENGTH ON CONNECTING PERFORMANCE OF CMC SINGLE LAP JOINT

The effect of through-thickness reinforcement by composite pins （Z-pins） on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite （CMC） is investigated. Overlap length of the single lap joint is 15 mm, 20 mm, 23 mm, 37 mm, and 60 mm, respectively. The experimental results indicate that the final failure modes of the joints can be divided into two groups, （a） the bond-line stops debonding until crack encounters Z-pins; and then the adherends break at the location of Z-pins, when overlap length is more than 20 mm; （b） the bond-line detaches entirely and Z-pins are drawn from adherends, when overlap length is equal to 15 mm. A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints. Here, the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of complete failure mechanisms, for example, bond-line initial delamination and ultimate failure associated with Z-pin pullout, ultimate failure of the adherends. The paper simulates connecting performance of the single lap joints with different Z-pins＇ diameter, spacing and overlap length; the numerical results agree with the experimental results; the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints. By numerical analysis method, the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm, when Z-pins＇ diameter and spacing are 0.4 mm, 5 mm, respectively.

Influence of geometric parameters on stress concentration factors of undermatched butt joint with single V-groove under three-point bending load

In order to improve the bending load-carrying capacity （BLCC） of undermatched butt joint under three-point bending load, the influence of joint geometric parameters on stress concentration factors （SCF） at the weld bottom center and the weld toe of uudermatched butt joint with single V-groove are studied respectively based on the finite element method in this paper. Results show that the reinforcement height and the cover pass width play decisive role in the BLCC for undermatched butt joint. BLCC of undermatched butt joint can be improved by choosing the appropriate joint geometric parameters.

Configuration Analysis of Metamorphic Mechanisms Based on Extended Adjacency Matrix Operations

The adjacency matrix operations,which connect with configuration transformation correspondingly,can be used for analysis of configuration transformation of metamorphic mechanisms and the corresponding algorithm can easily be simulated by computer.But the adjacency matrix based on monochrome topological graph is not suitable for the topological representation of mechanisms with multiple joints.The method of adjacency matrix operations has its own limitations for analysis of configuration transformation of metamorphic mechanisms because it can only be used in the topological representation of mechanisms with single joints.In order to overcome the drawback of the adjacency matrix,a kind of new matrix named as extended adjacency matrix is proposed to express topological structures of all mechanisms.The extended adjacency matrix is not only suitable for the topological representation of mechanisms with single joints,but also can be used in that of mechanisms with multiple joints.On this basis,a method of matrix operations based on the extended adjacency matrix is proposed to analyze the configuration transformation of metamorphic mechanisms.The method is not only suitable for configuration analysis of metamorphic mechanisms with single joints as well as metamorphic mechanisms with multiple joints.The method is evaluated by calculating two examples representing metamorphic mechanisms with single joint and multiple joints respectively.It can be concluded that the method is effective and correct for analysis of configuration transformation of all metamorphic mechanisms.The proposed method is simple and easy to be achieved by computer programming.It provides a basis for structural synthesis of all metamorphic mechanisms.

A CFD Study on a Biomimetic Flexible Two-body System

By studying the characteristics of the flow field around a swimming fish,useful insights can be obtained into the superior swimming capabilities developed by nature over millions of years,in comparison to what can be achieved using the standard engineering principles traditionally employed in naval and ocean engineering.In the present study,the flow field related to a single joint fish model is simulated in the framework of a commercial computational fluid dynamics software(ANSYS Fluent 18.0).The principle of the anti-Kármán vortex street is analyzed and the relationship between the direction of the tail vortex and the direction of the fin swing is determined according to the vortex structures and the pressure distribution.A parametric investigation is finally conducted to analyze in particular how the Strouhal number(St)can affect the fish propulsive performance and efficiency。

Mechanical behaviour of adhesively single lap joint under buckling conditions

Adhesive Single Lap Joints have been subjected to tensile and bending investigations by many researchers. However, the joint is also likely to experience buckling loading in some aerospace applications. The aim of this work is to investigate the joint behaviour under quasi-static buckling conditions. For this purpose, the joints with three different adherend thicknesses and 25 mm overlap length were tested using two different types of adherends and an adhesive film. They were modelled using a non-linear Finite Element Method via the ABAQUS Explicit package programme.Load to failure and stress distributions in the joints were predicted and compared with the experimental results, which were found in a good agreement. The adhesive layer in the joint was assumed to experience shear stresses under the buckling mode, similar to that in tensile loading, yet, the stress concentrations at the ends of the overlap, the main cause of the failure, resulted in different effects on the joint performance;for the buckling mode the critical stresses were in compression but for the tensile case in peeling. Unlike the latter, the former was found to prevent failure of the layer depending on the adherend thickness, causing different failure mechanisms. There were two different failure modes of the joints;a complete failure in the adhesive layer and large plastic deformation of adherends which could be a good source for crashworthiness situations. Mechanical properties of the adherends were found to play important roles on the joint performance.

Physics-informed neural networks for estimating stress transfer mechanics in single lap joints

With the explosive growth of computational resources and data generation,deep machine learning has been successfully employed in various applications.One important and emerging scientific application of deep learning involves solving differential equations.Here,physics-informed neural networks(PINNs)are developed to solve the differential equations associated with a specific scientific problem.As such,algorithms for solving the differential equations by embedding their initial and boundary conditions in the cost function of the artificial neural networks using algorithmic differentiation must also be developed.In this study,various PINNs are adopted to estimate the stresses in the tablets and the interphase of a single lap joint.The proposed model is represented by two fourth-order non-homogeneous coupled partial differential equations,with the axial stresses in the upper and lower tablets adopted as the dependent variables.The axial stresses are a function of the tablet length,which presents the independent variable.Therefore,the axial stresses in the tablets are estimated by solving the coupled partial differential equations when subjected to the boundary conditions,whereas the remaining stress components are expressed in terms of axial stresses.The results obtained using the developed methodology are validated using the results obtained via MAPLE software.

Correlations of single photon emission computed tomography joints scan and bone metabolic markers in active rheumatoid arthritis

Objective To explore the correlation between quantitative value of joint bone scan by single photon emission computed tomography(SPECT)and serum bone metabolic markers in patients with active rheumatoid arthritis(RA).Methods Clinical data of 60 newly diagnosed RA patients were retrospectively collected in Department

Design of a Minimally Actuated Lower Limb Exoskeleton with Mechanical Joint Coupling

Powered lower limb exoskeletons have traditionally used four or more powered joints to provide ambulation assistance for individuals with spinal cord injury.Exoskeletons with numerous powered joints commonly lost some excellent features of passive orthoses and further decreased utility due to added weight and increased control complexity.This work adopts joints coupling mechanism to design a powered exoskeleton to minimize the number of actuated joints and control complexity.Unlike conventional powered exoskeletons,the joint-coupled-powered exoskeleton only has a single motor-actuated joint for each exoskeleton leg in conjunction with a unique knee coupled system to enable their users to walk,sit,and stand.And two types of joint coupled systems are designed,respectively,hip-knee coupled and knee-ankle coupled.The joint-coupled-powered exoskeleton system allows a single actuator to power the hip motion,and allows activate knee motion through the coupled motions of the hip or ankle.More specifically,when the mechanical coupled system is activated,the knee joint is unlocked,resulting in synchronized hip-knee or ankle-knee flexion and extension.The coupling mechanism is switched on and off at specific phases of the gait(the stance phase and the swing phase)to generate the desired motions.The research work proves that minimal actuated robotic systems with joint coupled could achieve safe and natural walking.