Study On Correlative Theory Of Impact Fatigue Testing Of Critical Components Of Firearms Automatic Mechanism And Impact Fatigue Test

The automatic mechanism is one of the most important components of firearms and its life affects the overall life of gun directly. The researches on failure results of automatic mechanism components indicate that impact fatigue is a critical factor. At present, the theory of firearms design in domestic field is undeveloped and the testing data of impact fatigue of the components is insufficient. It is essential to set up the impact fatigue testing system in order to study the viariation principle about impact fatigue life of the components. However, the impact fatigue testing machine specially designed for the components has not been manufactured on the current market. In this paper, a variety impact fatigue testing system is designed to satisfy the requirements of automatic mechanism components.The main machine of impact fatigue testing system is designed to be mechanical-structured in consideration of movement reliability of mechanism and cost. The most difficult part in this system is to design the loading mechanism of impact fatigue testing machine as the automatic mechanism impact testing has high requests for the amplitude, width and frequency of impact pulse. In this study, there are four mechanisms to be considered:crank-slipper mechanism making up of spring mass, crank connecting rod mechanism containing shifting fork, direct motion roller cam mechanism and double cams mechanism. The advantages and disadvantages of these mechanisms are compared and analied through simulating caculating. Finally, the special double cams flat slipper mechanism is adopted to be the loading mechanism. It is a modeled simulation model of the loading mechanism to analyse movement status of mechanism under the highest rotation velocity condition. A multi-objective optimization model is built, with the multi-population genetic algorithm based on the Pareto optimal theory, an optimization scheme is obtained.The force-pulse generator executes the impact loading on the sample in the impact fatigue testing through its punch. The contact between punch and sample influences the operation of system significantly. Modeling the two components both punch and sample finite element models and computing the impact process of punch with two shapes and three material, the variety principles of force-time, force-displacement, impulse-displacement and impulse-time about impact pulse are obtained, the relationships between the shape of punch and impact process of hyperelasto-elastic, elastic-elastic and elastic-plastic are analyzed.This paper sets up the engineering model of impact contact basing on nonline spring damping theory, and it is used to analyze the impact force, impact time and impulse of special material and shape under different impact mass and velocity. It is executed the impact testing on three materials of two shapes. The engineering model is modified according to the testing data and the results of correct model matches the testing data. The finite element model is built and introducted type of index numbers contact constraint conditions and the results of correct model match the testing data through adjusting the key parameters under constraint conditions.The testing machine finite element model is modeled. The simulation analysis results are used to operating characteristic analysis. The virtual engine model of the overall machine is built to analyses the stability of machine movement. Taking the clearance of guide rail working surfaces, the movement distance of slipper, impact velocity, punch shape and material as the analysis factors, taking the repetition of displacement of slipper and impact pulse as the analysis objects, the stability of impact fatigue testing machine is analized. The simulation numerical results indicate that the clearance of guide rail working surfaces and the movement distance of slipper affect the stability and others analysis factors only influence the impact pulse. The conclusion of orthotropic sensibility analysis which adopts the orthotropic experimentation is:the impact velocity has the most important influence and impact mass has the least influence on the impact pulse.The simulation model of impact fatigue life of automatic mechanism key components is built and local stress-strain method is adopted to estimate impact fatigue life of the bolt and barrel extension of 12.7mm sniping rifle, the extractor and firing pin of 95 type 5.8mm rifle and the locking plate of 12.7mm aerial machine gun. The life of components is estimated to about 10000 times and the results are consistent to the actual engineering experiment.The domestic first set of great tonnage and high frequence impact fatigue testing model machine of automatic mechanism components has developed. The mechanism movement is stable and reliable. The mechanism can simulate the actual working conditions of critical components of automatic mechanism of firearms, so it provides the powerful technological means for impact fatigue test of the critical components of automatic mechanism of firearms.