Compared to magnetorheological fluid, magnetorheological gel has better anti-settling performance and stability. Therefore, magnetorheological gel is suitable for devices that can meet operational requirements in all aspects after long-term storage, such as the anti-recoil application of weapons. To study this in-depth, the mechanism of the influence of magnetorheological gel micro-magnetic-mechanical properties on the macro-output damping mechanics of the damper, a parallel plate model of the mixed flow mode composed of Couette shear flow and Poiseuille pressure flow was established. The theoretical analysis was of the output damping of the damper. Finally, the controllability of the damper under impact load employed magnetorheological gel was preliminarily analyzed. The results indicate that the damping coefficient of the damper increases with the increase of dynamic viscosity ${\eta }_B$ of the magnetorheological gel, piston effective cross-sectional area $A_P$, magnetic pole $L$, and Bingham coefficient $Bi$. Magnetorheological damper has controllability under impact load and can reach a wide controllable range under the condition under small magnetic field ranging from 0 mT to 131 mT.

In this paper, the effect of temperature on rheological properties of magnetorheological (MR) gel is investigated under rotational steady shear and oscillatory dynamic shear. A kind of fluid-like MR gel (MRG) was firstly synthesized by mixing carbonyl iron powder (CIP) with polymer matrix. Then, the relationship between yield stress, normal stress of MRG and shear rate under six temperatures and four magnetic field strengths were studied by rotational shear experiments. The results demonstrate that the dependence of shear stress on temperature displays an opposite tendency in comparison with that of normal stress on temperature. Moreover, maximum yield stress, one of the most important parameter of MR materials, decreases with the increment of temperature. Under oscillatory dynamic shear test, storage and loss moduli and normal stress of MRG all increase with temperature when a magnetic field is applied, which presents a contrary trend in the absence of a magnetic field. Related mechanisms about the alternation of microstructures of MRG were proposed to explain the above-mentioned phenomena. This paper is helpful in fabricating semi-active engineering devices using MR materials as a medium.

Cranes are mechanical devices widely used to hoist materials in engineering. The box girder of a bridge crane is formed by welding. During welding, residual stress and welding deformation will be inevitably generated due to the instantaneous hot temperature, which will affect not only the camber of the crane but also the operational performance of the traveling trolleys. Therefore, understanding the laws governing the welding deformation can lead to better control of camber cutting of the crane web to avoid unnecessary corrections, reasonably control the geometry shape of the girder and ensure the good operational performances of the trolleys. To achieve this goal, thermal elasto-plastic analysis method together with the Abaqus software is used to analyze the welding from the upper and lower covers to the web, from the upper and lower steel angles to the web, and from the web to the ribs. For the welding simulations, Gaussian movable heat sources, with the advantages of low computational cost, fast calculation speed, easy convergence, and a reasonable number of segments, are selected. The simulation results are compared with the experimental results to verify the reliability, accuracy, and efficiency of the numerical welding model. Finally, the simulation results are discussed, and design guidance for the web is proposed.