Rod Deflection Research Articles

CROSS-PLY BENDING EQUATION AND APPLICATION FOR COMPRESSED ROD WITH CRACK

The aim of this paper is the analysis of rod cross‐ply bending and stability of rod systems in the presence of cracks. The power concept (its theoretical base is Maxwell's theorem about the reciprocity of displacements) and linear fracture mechanics methods for research of mechanical properties of rod systems in the presence of cracks nave been used. The main equation of the rod cross‐ply bending and the common solution of this equation were obtained. The expression of the relationship between rod deflection and the disturbing cross‐force was obtained. Some transcendental equation allows defining the inferior boundary of critical force of rod with a crack.

Experiments to assess structural loads during solid armature contact transition

The objective of the work is to characterize the force developed at the rail-armature interface during contact transition. Solid armatures were accelerated up to 2.5 km/s, with peak currents on the order of 1 MA. The armature contacts were allowed to naturally transition, an event that typically occurred on the decaying portion of the current pulse. Deflections of unsupported steel rods launched with an armature were measured from flash X-ray images taken at muzzle exit. In-bore X-rays were used on a few tests to refine the time at which the maximum rod deflection occurred. The highest velocity tests provided further data on armature deformation. In addition to the experiments, a coupled electromagnetic-structural dynamics code was used to compute the rod and armature deformations based on a range of assumed pressure profiles at the rail-armature interface and under a variety of boundary conditions. Reasonable agreement between the calculations and experiment was obtained with an interface pressure of approximately 550 MPa (80 ksi) applied over the smallest mesh area available at the leading edge of the front contact (25 kN). In future work, this load can then be used as input to structural mechanics calculations to further increase the survivability of hypervelocity long-rod penetrators.

Response of long rods to moving lateral pressure pulse: numerical evaluation in DYNA3D

In this paper a convenient method to study the response of long rod projectiles subjected to a traversing lateral load pulse is presented. This problem mimics the lateral interaction of a yawed projectile with an oblique plate target. There are certain numerical difficulties in using Lagrangian wavecodes directly to compute the lateral penetration interaction behavior associated with erosion of elements, which leads to apparent numerical instabilities and large scale lateral surface erosion of the penetrator. It is known from experiments that for low yaw angles, lateral erosion is absent. In such cases, we show that the plate target can be replaced by a loading pulse, which moves relative to the rod at a speed completely determined from the geometry. In addition to avoiding problems associated with erosion algorithm, this method results in a tremendous reduction in computation time due to absence of the target grid. Using this method, rod deflection is successfully computed, and fracture locations are identified.

On the rotating rod with variable cross section

Stability of a heavy rotating rod with a variable cross section is studied by energy method. Bifurcation points for the system of equilibrium equations are analyzed. It is shown that for the case when the rotation speed exceeds the critical one, the trivial solution ceases to be the minimizer of the potential energy, so that rod loses stability, according to the energy criteria. Also, a new estimate of the maximal rod deflection in the post-critical state is obtained.

In-flight flexure and spin lock-in for antitank kinetic energy projectiles

A time-dependent analysis, coupling the rod vibration equation and pure roll motion equation, is formulated to numerically simulate the in-flight bending behavior of antitank kinetic energy projectile rods. The projectile is modeled as undergoing continuous, simulated planar pitching motion with the aerodynamic, spin, and structural damping forces included. The main parameter affecting the projectile spin and rod deflection responses is the fin torque producing the spin. Detailed spin, deflection, maximum stress, pitching angle, and rod shape histories are obtained along the projectile trajectory. Various steady-state spin cases are studied to simulate the effect of damaged fins. The spin lock-in phenomenon at the first lateral flexing natural frequency is captured by the present model for rods with simulated damaged fins. Any deformable projectile attempting, because of damaged fins, to spin past that frequency was found to lock-in to spinning at that frequency. Both suband supercritical spin cases are computed. Predictions of the rod shape at any instant and under actual flight conditions are made.