Re: [請益] 拉伸試驗的拉伸速率

看板Mechanical (機械)作者shoppinglin (瞎拼)時間15年前 (2010/10/06 11:16)推噓0(0推 0噓 0→)

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自己解決了問題幫自己回po一下希望能幫助到有用到的人 ※ 引述《shoppinglin (瞎拼)》之銘言： : 目前是看最新版的E8/E8M : 以下文字有點多可先直接看段落下方中文 : 擷取部分文字因為我有點被搞混到底想知道YS UTS ELONGATION : 的速率規定是上限還固定還下限 : 7.6.3 Speed of Testing When Determining Yield Properties— : Unless otherwise specified, any convenient speed : of testing may be used up to one half the specified minimum : yield strength or up to one quarter of the specified minimum : tensile strength, whichever is smaller. : 上限為1/2的決定YS速率or1/4的決定UTS用速率兩者較小值? : 還是說另外有規定specified YSmin的速率為多少? 這裡應該是說在應力到達1/2YS or 1/4UTS(看哪個小) 之前速率並不重要都可以 : The speed above this point shall be within the specified limits. 超過這個應力值之後就必須加以規範(有上下限) : If different speed limitations are required for use in determining : yield strength,yield point elongation, tensile strength, elongation, : and reduction of area, they should be stated in the product specifications. 用不同速率決定不同性質時必須加以說明 : In all cases, the speed of testing shall be such that the forces : and strains used in obtaining the test results are accurately indicated. : Determination of mechanical properties for comparison : of product properties against a specification value should : be run using the same control method and rate used to : determine the specification value. : 想同時取得YS UTS的機性應用同一種方法及速率(但之後卻又分別有規定? 應該是比較同性質時要取用一樣的拉伸速率 : ====================================================== : 7.6.3.3 Control Method C—-Crosshead Speed Control : Method for Determining Yield Properties– : The testing machine shall be set to a crosshead speed equal : to 0.015正負0.003 mm/mm/min [in./in./min] of the original reduced section : ====================================================== : 7.6.4 Speed of Testing When Determining Tensile Strength— : When determining only the tensile strength, or after the yield behavior : has been recorded, the speed of the testing machine shall be set between : 0.05 and 0.5 mm/mm [or in./in.] of the length of the reduced section : (or distance between the grips for specimens not havinga reduced section) : per minute. ====================================================== 後來才看到早該發現的ASTM A370 附上速率的一小節原文 7.4 Speed of Testing—The speed of testing shall not be greater than that at which load and strain readings can be made accurately. In production testing, speed of testing is commonly expressed: (1) in terms of free running crosshead speed (rate of movement of the crosshead of the testing machine when not under load), (2) in terms of rate of separation of the two heads of the testing machine under load, (3) in terms of rate of stressing the specimen, or (4) in terms of rate of straining the specimen. The following limitations on the speed of testing are recommended as adequate for most steel products: NOTE 2—Tension tests using closed-loop machines (with feedback control of rate) should not be performed using load control, as this mode of testing will result in acceleration of the crosshead upon yielding and elevation of the measured yield strength. 7.4.1 Any convenient speed of testing may be used up to one half the specified yield point or yield strength. When this point is reached, the free-running rate of separation of the crossheads shall be adjusted so as not to exceed 1/16 in. per min per inch of reduced section, or the distance between the grips for test specimens not having reduced sections. This speed shall be maintained through the yield point or yield strength. In determining the tensile strength, the free-running rate of separation of the heads shall not exceed 1/2 in. per min per inch of reduced section, or the distance between the grips for test specimens not having reduced sections. In any event, the minimum speed of testing shall not be less than 1/10 the specified maximum rates for determining yield point or yield strength and tensile strength. 7.4.2 It shall be permissible to set the speed of the testing machine by adjusting the free running crosshead speed to the above specified values, inasmuch as the rate of separation of heads under load at these machine settings is less than the specified values of free running crosshead speed. 這句好亂= = 應該是指空拉的速率調到規定值不過要知道在有試片時會略低於此值? 7.4.3 As an alternative, if the machine is equipped with a device to indicate the rate of loading, the speed of the machine from half the specified yield point or yield strength through the yield point or yield strength may be adjusted so that the rate of stressing does not exceed 100 000 psi (690 MPa)/min. However, the minimum rate of stressing shall not be less than 10 000 psi (70 MPa)/min. 這個就要看reduced section長度跟young's modulus 去推算strain rate or grip separation speed PS 鋼材大約E=200GPa 原來有這麼多東西我現在才發現= = 我用的strain rate 大約是0.24/min 大概符合決定UTS的速率不過完全大於690MPa/min(約=0.00345) 不過拉出來E反而是偏低很多可能是因為我用螺紋的試棒有空隙一開始的strain不是從reduced section來的 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 123.204.71.22 ※ 編輯: shoppinglin 來自: 123.204.71.22 (10/06 11:30) ※ 編輯: shoppinglin 來自: 123.204.71.22 (10/06 11:30)