Optimization of anti-loosening bolt based on double thread mechanism: Development of ground rolling die and effect of thread accuracy on loosening resistance.

We have devised innovative anti-loosening bolts with a double thread-mechanism (denoted DTB-IIC) composed of coaxial single and multiple coarse threads. In this study, we first developed a high-speed and high-precision grinding system for dedicated thread rolling dies of the DTB-IIC. Compared to conventional electro-discharge machining dies, ground dies significantly reduced processing time and costs, and achieved more than 10 times higher durability in thread rolling tests. Comparative Junker vibration loosening tests based on an ISO standard were conducted on several types of DTB-IICs. The amount of backlash δ between the inner multiple-thread nut and DTB-IIC bolt has a great effect on the initial drop of the bolt axial preload, and the rolled DTB-IIC with a relatively small δ secured a residual axial load rate of ≥85%, which satisfies the rating-1 of good self-locking behavior. A 3D FEM model was employed to simulate the initial loosening process in the Junker test, and the analytical results agreed well with the experimental ones by adjusting δ appropriately. Both experimental and analytical results indicate that the high loosening resistance of DTB-IIC is due to the synergistic effect of the interference mechanism of two types of nuts and the jammed locking state.

Analysis of ESAFORM 2021 cup drawing benchmark of an Al alloy, critical factors for accuracy and efficiency of FE simulations.

This article details the ESAFORM Benchmark 2021. The deep drawing cup of a 1 mm thick, AA 6016-T4 sheet with a strong cube texture was simulated by 11 teams relying on phenomenological or crystal plasticity approaches, using commercial or self-developed Finite Element (FE) codes, with solid, continuum or classical shell elements and different contact models. The material characterization (tensile tests, biaxial tensile tests, monotonic and reverse shear tests, EBSD measurements) and the cup forming steps were performed with care (redundancy of measurements). The Benchmark organizers identified some constitutive laws but each team could perform its own identification. The methodology to reach material data is systematically described as well as the final data set. The ability of the constitutive law and of the FE model to predict Lankford and yield stress in different directions is verified. Then, the simulation results such as the earing (number and average height and amplitude), the punch force evolution and thickness in the cup wall are evaluated and analysed. The CPU time, the manpower for each step as well as the required tests versus the final prediction accuracy of more than 20 FE simulations are commented. The article aims to guide students and engineers in their choice of a constitutive law (yield locus, hardening law or plasticity approach) and data set used in the identification, without neglecting the other FE features, such as software, explicit or implicit strategy, element type and contact model.

Development of a biaxial tensile testing machine for pulsed neutron experiments.

A biaxial tensile testing method has been used to get macroscopic information on elastoplastic deformation of a thin steel specimen and improve the accuracy of plastic processing of steel materials. We newly developed a biaxial tensile testing machine for pulsed neutron experiments (BTM-NEU) to provide the microscopic crystallographic information of steel materials under biaxial load and correlate it with the macroscopic mechanical properties of the materials. The performance of the BTM-NEU was experimentally evaluated with cold-rolled mild steel and hot-rolled high-tensile-strength steel materials and compared with that of a standard biaxial tensile testing machine (BTM-std) as follows. •The BTM-NEU can test an ISO-standardized cruciform specimen as the BTM-std and its performance is equivalent to that of the BTM-std.•The BTM-NEU has excellent long-time reliability and stability necessary for pulsed neutron experiments, especially Bragg-edge neutron imaging experiments.•The BTM-NEU can be applied to pulsed neutron experiments using a Bragg-edge imaging method.