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In this study, an analytical approach based on the energy method is used to estimate the force required to expand tubes for different die shapes. The proposed method calculates the driving force by the volume energy change and working effect ratio instead of depending on the contact pressure and the shape of the contact surface in the previous studies. The new approach greatly reduces the difficulty of the analysis and simplifies the calculation. Since the accurate stress distribution in the transition zone is essential for determining the working effect factor, a new analytical approach with self-adaption is also introduced to estimate the strain and stress distribution in the transition zone of an expanding tube, and the contact position between die and tube can also be obtained by this approach. In this study, three finite element models as a numerical approach are used to develop an axisymmetric model including multiple linear kinematic hardening behavior to confirm the approach. Additionally, copper and steel 3/8 inch tubes are expanded with oval dies on a designed test workbench with different boundary conditions. The tangential, longitudinal strains and driving force are monitored and recorded during the expansion process. Finally, the results from the three approaches show a very good agreement.

Accurate prediction of the relative biological effectiveness (RBE) of boron neutron capture therapy (BNCT) is challenging. The therapy is different from other radiotherapy; the dynamic distribution of boron-containing compounds in tumor cells affects the therapeutic outcome considerably and hampers accurate measurement of the neutron-absorbed dose. Herein, we used boron-containing metal–organic framework nanoparticles (BMOFs) with high boron content to target U87-MG cells and maintain the concentration of the 10B isotope in cells. The content of boron in the cells could maintain 90% (60 ppm) within 20 min compared with that at the beginning; therefore, the accurate RBE of BNCT can be acquired. The effects of BNCT upon cells after neutron irradiation were observed, and the neutron-absorbed dose was obtained by Monte Carlo simulations. The RBE of BMOFs was 6.78, which was 4.1-fold higher than that of a small-molecule boron-containing agent (boric acid). The energy spectrum of various particles was analyzed by Monte Carlo simulations, and the RBE was verified theoretically. Our results suggested that the use of nanoparticle-based boron carriers in BNCT may have many advantages and that maintaining a stable boron distribution within cells may significantly improve the efficiency of BNCT.

As a crucial component, rolling bearings directly determine the reliability of rotating equipment. However, current dynamic models for predicting the bearing performance either ignore the velocity and stress dispersion at the ball/raceway interface or fail to consider the spin moment generated within the interface. To address this issue, the discrete features of the velocity and stress distribution are considered in this paper, and the micro-element approach is used to construct formulas to obtain the traction vectors in two and three dimensions, respectively. Two bearing dynamic models are further developed for these two types of equations: one model considers the spin moment at the interface owing to unequal contact angles between the ball and the two raceways, while the other model ignores this moment. The reliability of these models is validated by comparison with experimental test results, including cage speed and oil film thickness. The predictions from the quasi-static model are used as theoretical values to compare the ability of the two models to simulate bearing performance under different operating conditions. The results show that the prediction results of the model considering the spin moment are closer to the theoretical values than those of the model ignoring this moment. However, the moment increases the friction at the ball/raceway interface, causing this model to underestimate the extent of bearing sliding.

The initial loss of tension in individual bolts after initial tightening obviously affects the level and the stability of the clamp load in bolted joints. A high-precision instrument to analyze the clamp load loss was developed. In this instrument, an Atlas Copco’s high performance spindle with an accuracy of ±2.5% under the conditions of one million duty cycles was used to tighten the test bolts and nuts. A rotary torque-angle transducer was integrated in the tightening spindle to measure the tightening torque. KMR force washer with a repeatability of < ±1% was applied to monitor the clamping force in real time. Using this instrument, the design of experiment analysis was performed to determine the effect of variables on the initial loss of tension. Those variables included the joint materials, the fastener class, the gasket grade, the lubrication, the surface roughness, the tightening speed, and the number of repeated tightening. The results showed that the tightening speed and the number of repeated tightening had a significant effect on the initial loss of tension. Moreover, a process criterion of eliminating plastic deformation was proposed to minimize the initial loss of tension. The findings presented in this paper will be expected to enhance the reliability and the safety of bolted assemblies, especially in critical applications.

Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.

The loading contact behaviour of ellipsoids has been extensively studied, although there is limited research on their loading and unloading contact behaviour. This study uses the finite element method to analyse loading and unloading contact between an elastic-plastic ellipsoid and a rigid body. Unloading of an ellipsoid with different ellipticities was precisely conducted at the end of the elastic-plastic state. The ellipticity of the contact area is related to interference during loading and is independent of interference during unloading. When the interference is sufficiently large, the ellipticity of the contact area asymptotically approaches that of the ellipsoid. A new empirical formula is presented to describe the residual plastic interference of the ellipsoid after elastic-plastic unloading. The ellipsoid contact parameters (contact pressure, contact load, interference, and contact area) during the loading and unloading processes are numerically fitted based on the finite element analysis results, and dimensionless expressions are proposed for practical applications. The correctness and validity of the current study are evaluated through comparison with the prediction results of previous models and experiments.