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Nonlinear Material Behavior Analysis under High Compression Pressure in Dynamic Conditions 时间:2017-09-08 11:57 来源:未知作者:admin 点击: 次 Abstract:Gun chamber pressure is an important parameter in proofing of ammunition to ensure safety and reliability. It can be measured using copper crushers or piezoelectric sensor. Pressure calculations in copper crusher method are based on linear plastic deformation of copper after firing. However, crusher pressure deformation at high pressures deviates from the corresponding values measured by piezoelectric pressure transducers due to strain rate dependence of copper. The nonlinear deformation rate of copper at high pressure measurements causes actual readings from copper crusher gauge to deviate from true pressure values. Comparative analysis of gun chamber pressure was conducted for 7.62 × 51 mm ammunition using Electronic Pressure, Velocity, and Action Time (EPVAT) system with piezoelectric pressure transducers and conventional crusher gauge. Ammunitions of two different brands were used to measure chamber pressure, namely, NATO standard ammunition and non-NATO standard ammunition. The deformation of copper crushers has also been simulated to compare its deformation with real time firing. The results indicate erratic behavior for chamber pressure by copper crusher as per standard deviation and relative spread and thus prove piezo sensor as more reliable and consistent mode of peak pressure measurement. The results from simulation, cost benefit analysis, and accuracy clearly provide piezo sensors with an edge over conventional, inaccurate, and costly method of copper crusher for ballistic measurements due to its nonlinear behavior.
1. Introduction
Proof is a destructive test in which small numbers of proof samples are selected as representative of a large group known as lot or batch of the ammunition by the same manufacturer and process. Proofing of ammunition is important to ensure the safety, reliability, and operational effectiveness of conventional ammunition. The importance of proofing is often poorly understood, leading to failure in ammunition safety and stability. Proof of ammunition is a systematic method of evaluating the properties, characteristics, and performance capabilities of ammunition throughout its life cycle. It is used to assess the reliability, safety, and operational effectiveness of stocks. Proof is the functional testing or firing of ammunition and explosives to ensure safety and stability in storage and intended use. In-service proof and the surveillance of ammunition are undertaken to ensure that the ammunition continues to meet the required quality standards throughout its life [1].
The acceptance or rejection criterion during test firing of guns and ammunitions depends upon many factors. Chamber pressure is defined as the force per unit area that explosive gas exerts on the walls of a gun chamber. Chamber pressure being the most important, researchers have been making unremitting efforts to improve the testing precision [2] as this must be tested and verified during research and development of product acceptance.
Crusher gauges were used to measure gas chamber pressure as commonly available standardized method till 1960s [3]. Usually a piston fitted to a piston hole into the chamber of the barrel compresses a copper or lead cylinder. The crusher gets permanently deformed due to the effect of the gas pressure generated by the burning of the explosive mixture on the base of the piston. After measuring the deformed crusher length, the peak pressure is estimated after comparing it to a calibrated conversion table provided by the manufacturer with each lot of crushers. Though convenient, it is incapable of recording the dynamic change of chamber pressure with time. Figure 1 shows piezo sensor and conventional cylindrical copper crusher.