Resumen en Inglés:

Abstract The characteristics of a bullet are closely related to its shooting accuracy. In actual shooting, the centroid and entry angle of the bullet always deviate from the ideal state. To study the influence of these two parameters on the movement of the bullet, a finite element model of the bullet movement inside the barrel was built based on a 5.8 mm small-caliber rifle to simulate the actual process of firing bullets. In this model, the pressure load of the real gunpowder gas on the bullet was considered. This model was also verified by experiments and the relative error is less than 1.5%. The result shows that the influence the centroid and entry angle of the bullet are mainly reflected in the amplitude and phase angle of the bullet swing angle. The larger the offsetting distance of cetroid is, the amplitude of the pitch and yaw angle are. The maximum magnitude of amplitude is 0.2°. The difference of swing angle in phase is equal to the difference in offsetting angle. The curve characteristics of different deviation angle are similar to the curve of bullet cetroid effect. The range of the pitch angle is -1°~0.9° and the range of the yaw angle is -0.9°~0.9°.

Resumen en Inglés:

Abstract This study presents an experimental investigation on the contribution of carbon fiber-reinforced polymer (CFRP) sheets in shear-strengthened beams with different strengthening schemes. Three different reinforcement types and strengthening schemes are applied (U-shaped, U-shaped with additional anchorage and fully-wrapped). The strength contribution of FRP sheets, internal stirrups, and concrete are estimated based on experimental data. Two different anchoring strategies to prevent the FRP strengthening from debonding were also present, using horizontal strips of FRP and rebars on grooves on the web of the beams. The behavior of each of the beams is discussed in terms of load-displacement, failure mode, strains distribution, cracking pattern, and shear force contribution. The influence of the strengthening configuration and FRP anchorage on the FRP shear contribution and total shear resistance is discussed based on the experimental. The individual contribution of FRP, stirrups and concrete are estimated based on strain data from the tests. Finally, the experimental shear capacity is compared to the recommendations of ACI 440.2R, and fib Bulletins 14 and 90.

Resumen en Inglés:

Abstract This paper presents a new triangular multi-layer nonlinear shell finite element with incremental degrees of freedom, suitable for large displacements and rotations. This is a nonconforming element with 6 nodes, quadratic displacement and linear rotation field based on Rodrigues incremental rotation parameters, with a total of 21 DoFs. The novelty of this element is the extension to a multilayer, fully incremental situation of the T6-3iKL element, a kinematical model with properties from Kirchhoff-Love theory, approximating the shell director across layers as constant. The model is numerically implemented, and results are compared to different references in multiple examples, showing the capabilities of the formulation. It is believed that the possibly simplest multilayer extension, combined with fully incremental DoFs, simple kinematic, no necessity of artificial parameters such as penalties, a relatively small number of DoFs, possibility to use various 3D material models, easily connected with multiple branched shells and beams, and geometric exact theory create a simple yet powerful shell element.

Resumen en Inglés:

Abstract The surrounding rock stiffness has a significant effect on the impact mechanical properties of rockbolts. In order to study the influence of radial stiffness of surrounding rock on the dynamic characteristics of the end-anchored rockbolt, numerical simulations of drop weight impact tests on the end-anchored rockbolt were conducted using finite element method. The simulation results show that the larger the radial stiffness of the surrounding rock, the larger the value of the absorbed impact energy of end-anchored rockbolt. However, there is an upper limit to the effect of radial stiffness on the dynamic behavior of end-anchored rockbolt, i.e., the value of absorbed impact energy tends to be stabilized when the radial stiffness exceeds 2.91 GPa/mm. In the impact simulation, the fracture position of the bolt bar is affected by both radial stiffness and impact energy. The greater the radial stiffness of the surrounding rock, the further the fracture location is away from the anchorage end. The larger the impact energy is, the closer the fracture location is to the anchorage end. It is important to study and determine the range of fracture location of anchor rods to develop new types of anchor rods and to design the support scheme for the surrounding rock under dynamic loading. Finally, due to the linkage between numerical simulation and indoor tests, the effect of steel pipe wall thickness on the upper and lower limits of the results also provides a theoretical basis for the rationalization of the design of steel pipe wall thickness. The study of dynamic impact fracture location of bolt bar is of great significance for the development and design of new types of rockbolt under dynamic loading.