Experimental Measurement of Neck Formation Time and its Probabilistic Model Description

The paper considers the phenomenon of strain localisation (neck formation) in flat tensile specimens undergoing high-temperature creep. Localisation is known to cause the material to lose its bearing strength, becoming unable to withstand the loads applied; subsequent strain mostly occurs locally in the neck. Only approximate theoretical estimates of neck formation time are possible during such testing. Our experiments investigated flat aluminium alloy specimens using an original instrument for non-contact high-temperature measurements that allowed us to measure the specimen geometry and displacement of its surface points over the course of our high-temperature experiment. We obtained experimental neck formation times for various initial tensile stresses and values of the parameter indicating sensitivity to necking. We considered the natural distribution of creep data in terms of statistics. We used the normal distribution to develop a probability density model of neck formation time. We computed theoretical probability of neck formation during a given period of time and described a method for estimating reliability, that is, work not involving strain localisation

The study was partially supported by RFBR grant (project no. 16-38-60200) and grant of the President of the Russian Federation (MK-4321.2018.1)

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