Exploring the Effect of Asperity Order on Mechanical Character of Joint Specimen from the Perspective of Damage

The joint morphology is multiscale. The effect of each asperity order on the mechanical properties of joints is different. The shear mechanical properties of joint specimens are related to its surface damage characteristics. At present, there are still few studies on the effect of roughness on the shearing mechanical properties of joint from the perspective of damage of each asperity order. In this paper, the standard roughness profile was chosen as initial morphology. The standard roughness profile was decomposed into waviness and unevenness by the method combine the ensemble empirical mode decomposition (EEMD) and the cut-off criterion. Then, the joint specimen which contains waviness and unevenness and the specimen which only contains waviness were prepared by the 3D engraving technology. The 40 sets of joint specimens with different asperity order were subjected to direct shear tests under different normal stresses. Based on the 3D scanning technology and ICP iterative method, the damaged area and the damage volume were calculated. Based on the damage volume data and the acoustic emission (AE) data, the effect of asperity order to the joint mechanical behaviour was studied. The results indicate that (1) under low normal stress, the unevenness plays a control role in the failure mode of the joint specimen. Under low normal stress, the joint surface containing only waviness exhibits slip failure, and the joint surface with unevenness exhibits shear failure. With the increase of the normal stress, the failure mode of the specimen containing only waviness changes from slip failure to shear failure; (2) the unevenness controls the damage degree of the joint specimen. The damaged area, damage volume, AE energy rate, and accumulative AE energy of the joint specimen with unevenness are larger than those of the specimen with only waviness, and this difference increases with the normal stress increase; (3) the difference between the joint specimen with unevenness and specimen with only waviness mainly exists in the prepeak nonlinear stage and the postpeak softening stage. The characteristic parameters of acoustic emission generated in the postpeak softening stage of the joint specimen with unevenness are greater than those of the specimen with only waviness. This phenomenon can be used to explain the stress drop difference at the postpeak softening stage; (4) the AE b value can be used to evaluate the damage of joint specimens. Analysing the damage difference of each asperity order under different normal stresses is of great significance to the analysis of the influence of the morphology of the joint surface on the mechanical properties of the joint.

Modelling on Reinforced Concrete Exterior Joint with Simplified Detailing Technique by Using Coupler Bar

The present study focus on structural response of the Reinforced Concrete (RC) beam-column joint through numerical studies. For this study, totally two groups of reinforcement details are considered and named as “EJ-SFC” and “EJ-IS456”. The proposed coupler joint specimen (EJ-SFC) is compared with the standard detailed specimen that is design and detailed by IS 456-2000. To simulate each group of the specimen, a full 3D Finite Element Modelling (FEM) analysis has been carried out by using ANSYS 14.5 software. All groups of joints were tested under reverse cyclic loading. The outcome of the Finite Element Analysis (FEA) findings were presented in terms of load - deflection plot and compared with previous experimental results. The FEA and experimental results showed that the performance of the proposed coupler joint specimen was superior in ductile behaviour than that of EJ-IS456 specimen.

Development of a New Method for the Quantitative Generation of an Artificial Joint Specimen with Specific Geometric Properties

A rock joint is a planar discontinuity that has significant influence on the mechanical and hydraulic characteristics of rock mass. Laboratory experiments are often conducted on a joint to investigate and provide fundamental information for rock mass analysis. Although joint roughness and mechanical aperture exert great effects on the experimental results, controlling them in quantitative manner is quite complicated and consumptive in terms of specimen preparation. A new and simple method for the quantitative generation of the joint specimen was proposed in this study. Based on random midpoint displacement method, a joint specimen with a void space inside was generated. Parametric studies for the roughness and mechanical aperture were carried out, and as a result, the two joint properties could be controlled by manipulating input parameters of random midpoint displacement method. In order to validate the proposed method, two joint specimens, which had different levels of roughness and aperture, were generated and printed. Surface coordinates of the specimens were obtained by a 3D laser scanner, and calculated to make a comparison between the target values and the estimated values. Results showed that the method was capable of generating joint specimens with satisfactory precision.

Numerical Analysis of Temperature Rise during Dynamic Loading for Dissimilar Steel Joint Specimen

In this study, dynamic temperature field in a dissimilar steel joint specimen was numerically analyzed by means of three-dimensional explicit finite element analysis. Fully coupled thermal stress analysis was performed by using FE-code Abaqus/Explicit ver. 6.12. It was assumed that 90% of the plastic work was transferred to heat. Furthermore, dynamic loading tests were conducted with three-point bending specimen extracted from the dissimilar steel joint between a mild steel and a high tensile strength class steel. The specimen included a U-shape notch in the bonded interface. A high-speed infrared camera was used to measure the temperature field near the bonded interface. The temperature field was recorded at a frame rate of 200 Hz during the dynamic loading test. The numerically calculated temperature field near bonded interface showed reasonable agreement with the temperature field measured by the high-speed infrared thermography. The temperature in the soft steel particularly increased during the dynamic loading. On the other hand, the increase in temperature in the hard steel area was relatively few.

Verification of the Computed Tomography Results of Aluminum Alloy Welded Joint

Computed tomography (CT) of aluminum welded joint specimen has been performed. On the tomographic cross sections some defects have been found. To verify them the metallography cross sections of welded has been done. It was found that selected defects are micro cracks.

A Case Study of a Cooling Pipe for a Pre-Cooler Used in a 70-MPa Hydrogen Station

A case study was conducted on the cooling pipe of a precooler which had been used in a 70-MPa hydrogen station demonstration project. The cooling pipe consisted of a main pipe, a mechanical joint pipe and a mechanical joint. The main and mechanical joint pipes had been joined using TIG welding. Through chemical composition analysis, microstructure observation and Vickers hardness measurement, it was revealed that the main and mechanical joint pipes had been manufactured from SUS316L and that 316L was the filler metal used for TIG welding. Round-bar specimens were machined out of the main pipe in order to investigate the tensile properties of the base metal. On the other hand, both round-bar specimen without reinforcement and square-bar specimens with reinforcement were fabricated from the weld-joint. Using the three types of specimens, slow strain rate tensile tests were performed in 0.1 MPa nitrogen gas and in 115 MPa hydrogen gas at a temperature of −40 °C. Reduction of area (RA), φ, for the round base-metal specimen, the round weld-joint specimen and the square weld-joint specimen were respectively, 83.5 %, 71.3 % and 81.4 % in nitrogen gas, whereas the related values in hydrogen gas were 60.1 %, 61.3 % and 40.1 %. In other words, the RA for the three types of specimens was smaller in hydrogen gas than in nitrogen gas. Dimples were formed on the fracture surfaces of the three specimen types in nitrogen gas, whereas both dimples and quasi-cleavages were formed in hydrogen gas.