ASME STP-PT-080-2016 DEVELOPMENT OF AVERAGE ISOCHRONOUS STRESS-STRAIN CURVES AND EQUATIONS AND EXTERNAL PRESSURE CHARTS AND EQUATIONS FOR 9CR-1MO-V STEEL.pdf
《ASME STP-PT-080-2016 DEVELOPMENT OF AVERAGE ISOCHRONOUS STRESS-STRAIN CURVES AND EQUATIONS AND EXTERNAL PRESSURE CHARTS AND EQUATIONS FOR 9CR-1MO-V STEEL.pdf》由会员分享,可在线阅读,更多相关《ASME STP-PT-080-2016 DEVELOPMENT OF AVERAGE ISOCHRONOUS STRESS-STRAIN CURVES AND EQUATIONS AND EXTERNAL PRESSURE CHARTS AND EQUATIONS FOR 9CR-1MO-V STEEL.pdf(119页珍藏版)》请在麦多课文档分享上搜索。
1、DEVELOPMENT OF AVERAGE ISOCHRONOUS STRESS-STRAIN CURVES AND EQUATIONS AND EXTERNAL PRESSURE CHARTS AND EQUATIONS FOR 9CR-1MO-V STEELSTP-PT-080STP-PT-080 DEVELOPMENT OF AVERAGE ISOCHRONOUS STRESS-STRAIN CURVES AND EQUATIONS AND EXTERNAL PRESSURE CHARTS AND EQUATIONS FOR 9Cr-1Mo-V STEEL Prepared by: M
2、AAN JAWAD, Ph.D., P.E. Global Engineering at other conditions tertiary creep is important. The model must in some cases be predictive of conditions for which there are no available data, specifically estimating creep strains at very low stresses, high temperatures, and long times. In describing the
3、model, we try to maintain a distinction between terms such as condition, parameter, constant, and coefficient. The conditions are the inputs to the model: stress, temperature, and time. The parameters of the model are the values that are used to describe the shape of the creep curve at a specific se
4、t of conditions. For example, the stress exponent, n, is a parameter, and the time to rupture, tr, may also be considered a parameter. The model coefficients are used in describing the parameters as functions of stress and temperature. The term constant is only used for specific coefficients that ta
5、ke on a special role in a time-temperature parameterization. In this report, the term constant is exclusively used for the Larson-Miller constant. It is highly desirable to keep the number of parameters low to minimize the effort of determining the coefficients. Many have come to view the classic th
6、ree stage description of creep as the result of a primary stage where hardening mechanisms result in diminishing creep rates and a tertiary creep stage where damage and aging mechanisms produce an increasing creep rate. The second stage, where creep rate appears to be constant, is simply the transit
7、ion between the two stages. Primary-tertiary forms for creep models often involve four parameters, two each for the primary and tertiary stages. To determine these parameters, three approaches are possible. The first is to fit the entire curve. This can be quite difficult depending on the creep mode
8、l since it involves non-linear regression. The second is to fit either the tertiary creep or primary creep and then make adjustments for the missing component. The third is to fit each separately and look for a method to combine the curves. The model proposed below seeks to use information contained
9、 within the tertiary creep portion of the curve to provide an estimate of the primary creep strain. 1.2 Logarithmic Creep Rate Formulation Description of Tertiary Creep The model expression for tertiary creep is1 303lnln (1.1) where is the creep strain, is the creep strain rate,03 represents the ini
10、tial creep rate at zero strain and 3 provides the dependence of the strain rate on the creep strain. In the present paper, we refer to this form of the creep law as the logarithmic-rate form. 1 The use of the term is intentional and is used to distinguish the resultant values in the present approach
11、 from those values tabulated for aged material in ASME FFS-1 / API-579. STP-PT-080: Isochronous Stress-Strain Curves and External Pressure Charts and Equations for 9Cr-1Mo-V Steel 2 Upon integration, assuming there is no initial strain or other stages of creep, equation (1.1) becomes2 t30333 1ln1 (1
12、.2) Then, the time to reach the rupture strain is 303exp1 rrt (1.3) Which for any combination, 33 r (1.4) can be approximated within 5% simply by the limit, 3031rt (1.5) At some conditions, the initial creep rate and the actual minimum creep rate are of the same order. In these situations, equation
13、(1.5) provides an estimate of the value of from minimum creep rate and time to rupture; furthermore, in such situations, 1/ 3 can be regarded as the Monkman-Grant strain. Description of Primary Creep and Combined Creep Strain It is recognized that primary creep is important under many conditions of
14、practical interest. Neglecting the early part of the creep curve could lead to significant errors, since the difference between the initial creep rate as derived from the latter stages of the creep curve and the actual minimum creep rate measured in a test can be orders of magnitude. A candidate exp
15、ression for the primary creep rate may be expressed in a similar form3: 101lnln (1.6) which leads to an expression for creep as t10111 1ln1 (1.7) In this case, the creep rate decreases with time and strain accumulation. Treating the tertiary and primary creep terms as independent contributions to th
16、e total creep strain leads to the following creep model: ttc 30331011 1ln11ln1 (1.8) 2 An early example of this equation can be found in Sandstrom, R. and Kondyr, “Model for Tertiary Creep in Mo- and Cr-Mo-Steels,” pp. 275-284 in Mechanical Behavior of Metals, Vol.2 Pergamon Press, New York, NY, 197
17、6. 3 Such a procedure was proposed in Cleh, J-P. “An extension of the omega method to primary and tertiary creep of lead-free solders,” Electronic components and technology conference, 2005. STP-PT-080: Isochronous Stress-Strain Curves and External Pressure Charts and Equations for 9Cr-1Mo-V Steel 3
18、 1.3 Ellis Creep Form Ellis took a related but subtly different approach to fitting a creep model. Starting with equation (1.1) he expressed the creep strain in the tertiary region as4: BtFA ln (1.9) where, 1A (1.10) and 0AB (1.11) which, when combined with equation (1.10) leads to 0B (1.12) Other t
19、han the integration constant, F, Elliss form of the equation is identical to equation (1.7). As will be shown, this integration constant is quite important in matching the tertiary creep parameters to the time to rupture. Ellis linearized the equation as BtFA /exp (1.13) The parameters are determine
20、d by adjusting the parameter A to minimize the R2 value of a linear regression to the tertiary portion of the creep curve. As might be expected, Ellis found that the rupture life corresponds very closely to the ratio F/B. To show this, consider failure to occur at a finite strain, then equation (1.1
21、0) becomes rr BtFA ln (1.14) and AFBt rr ex p1 (1.15) which, upon substitution of the equivalent tertiary creep parameters is identical to equation (1.3) if F = 1. As A greatly exceeded the rupture strain, equation (1.15) becomes BFtr (1.16) Or, from equation (1.12) 0Ftr (1.17) Thus this new paramet
22、er, F, appears in the rupture calculation. Using equation (1.16) allowed Ellis to make the substitution rtFB / (1.18) rtFtFA /ln (1.19) and, finally, 4 Originally, Ellis used the symbol C for the integration constant, but here, to avoid confusion with the Larson-Miller constant, we use the symbol F.
23、 STP-PT-080: Isochronous Stress-Strain Curves and External Pressure Charts and Equations for 9Cr-1Mo-V Steel 4 rttAFA /1lnln (1.20) Ellis then approximates the tertiary strain as rttA /1ln3 (1.21) Though the first term in equation (1.20), FAln , is constant, it can be replaced by the primary creep c
24、omponent. Ellis then used the Andrade form of the creep equation to characterize the primary creep: rc ttAKt /1ln3/1 (1.22) This form has the limitation of predicting an infinite strain rate at time=0. This model has three parameters, K, A, and tr; but rupture time has already been measured. Using t
- 1.请仔细阅读文档,确保文档完整性,对于不预览、不比对内容而直接下载带来的问题本站不予受理。
- 2.下载的文档,不会出现我们的网址水印。
- 3、该文档所得收入(下载+内容+预览)归上传者、原创作者;如果您是本文档原作者,请点此认领!既往收益都归您。
本资源只提供5页预览,全部文档请下载后查看!喜欢就下载吧,查找使用更方便
10000 积分 0人已下载
下载 | 加入VIP,交流精品资源 |
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- ASMESTPPT0802016DEVELOPMENTOFAVERAGEISOCHRONOUSSTRESSSTRAINCURVESANDEQUATIONSANDEXTERNALPRESSURECHARTSANDEQUATIONSFOR9CR1MOVSTEELPDF

链接地址:http://www.mydoc123.com/p-456978.html