Influence of gauge length on tensile curves of Gleeble high-temperature tensile samples
[Objective]The Gleeble thermal simulation machine is one of the main equipment for measuring the mechanical properties of metal materials under high-temperature conditions.During high-temperature tensile tests using the machine,the sample is locally heated.The highest temperature is at the center of the samples,decreasing with distance.Therefore,a temperature range of 50-100 ℃ is often selected as the gauge length to obtain the final tensile curves.For different samples,the gauge length is different.Selecting the appropriate gauge length is one of the key factors for obtaining highly accurate tensile curves.[Methods]In this study,the Gleeble-3500 was used to conduct relevant tests.Two types of bars and plates were selected as samples.The study focused on two main aspects.First,an electric couple wire was welded at the center of the samples to control their temperature.Additionally,two to four groups of thermocouples were welded at specific distances from the central positions to measure the sample temperatures.The samples were then heated and maintained at constant temperature.Temperature conditions were recorded,and time-temperature curves from different locations of the samples were obtained.The selected heating rate was 10 ℃/s.The three set temperatures were 600,800,and 1 000 ℃,respectively,with a holding time of 3 min.Four samples,including two bars and two plates,were subjected to high-temperature tensile tests to obtain the high-temperature tensile curves.These experiments were conducted at a rate of 0.1/s at 800 ℃.However,the four samples were stretched with different gauge lengths to obtain varying tensile curves.[Results]The study revealed the following:1)All four samples tested using the Gleeble-3500 machine exhibited localized heating characteristics at high temperatures.The highest temperature occurred at the center of the samples,and it decreased as the distance from the center increased.Moreover,the trend of temperature drop varied with the shape of the samples.The gauge length could be roughly judged according to the color change of the heated samples.However,the specific temperature differences still needed to be confirmed by actual measurement.2)In this study,the gauge length range of the two bars was smaller than that of the two plates.The recommended gauge length range that for bars S1 and S2 was 10-12 mm and 8-10 mm,respectively.In actual measurements,the temperature difference for bar S1 was more uniform than for bar S2.The recommended gauge length range for plates S3 and S4 was 35-40 mm and 40-45 mm,respectively.In actual measurements,the temperature difference of plate S4 was much more uniform than that of plate S3.3)For the same sample,the high-temperature tensile curves differed when different gauge lengths were selected.[Conclusions]Through a series of comparative experiments and detailed analysis,researchers can better understand how to use the Gleeble equipment to conduct high-temperature tensile tests.In this study,four samples,including two bars and two plates,were evaluated,and appropriate gauge length ranges were recommended for the four samples.The tensile curve results demonstrated the suitability of the recommended gauge lengths.
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