【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20190702
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Question: What are the two ways to express the metal creep limit? There are no answers provided for this series of posts; fellow netizens are free to share their own opinions – just reply with what you understand. Replies earn rewards ranging from 5 to 15 points; all forum members are welcome to participate actively and support the development of the forum! ! ! Chemical Equipment and Machinery
1. At a given temperature (T), the stress value that causes the specimen to exhibit a specified creep rate is expressed in kilogram-force per square millimeter; here, is the creep rate in the second stage, expressed as %/hour. 2. The stress value required to cause a certain amount of creep deformation (δ, %) in the specimen at a given temperature (T) and within a specified test time (t, hours) is expressed in units of kilogram-force per square millimeter.
The creep limit is the maximum constant stress at which the creep deformation or creep rate of the specimen, under specified temperature and time conditions, does not exceed a specified value. It has two ways of representation: one is the stress value that causes the specimen to exhibit a specified second-stage creep rate at a given temperature T. Another approach is to induce in the specimen a stress value corresponding to a certain creep strain within a given temperature T and specified time t.
There are two types of creep limits: one is the stress value that causes a specified steady-state creep rate at a specified temperature. The other is the stress value that causes a specified creep elongation at a specified temperature and within a specified testing time
①It is denoted by, where t is the test temperature (°C), τ is the test time (hours), and δ is the specified creep deformation amount (%). For example, =150 MPa means that the creep limit of a certain material is 150 MPa when the temperature is 600°C, the testing time is 100,000 hours, and the total strain resulting from creep is 1%. ②Expressed in symbols, where t is the test temperature (°C) and v is the creep rate in the second stage of creep (%/hour). For example, =100 MPa means that the creep limit of a certain material at a temperature of 700°C and a creep rate of (1/105)%/hour is 100 MPa.
One is the stress value that induces a specified steady-state creep rate at a specified temperature. The other is the stress value that causes a specified creep elongation at a specified temperature and within a specified testing time
1. At a given T, the stress value that causes the specimen to exhibit a specified creep rate, expressed in kilopounds per square millimeter (where it represents the creep rate in the second stage, %/hour). 2. The stress value required to cause a certain amount of creep deformation (δ, %) in the specimen at a given temperature (T) and within a specified test time (t, hours) is expressed in units of kilogram-force per square millimeter.
The creep limit is the maximum constant stress at which the creep deformation or creep rate of the specimen, under specified temperature and time conditions, does not exceed a specified value. It has two ways of representation: one is the stress value that causes the specimen to exhibit a specified second-stage creep rate at a given temperature T. Another approach is to induce in the specimen a stress value corresponding to a certain creep strain within a given temperature T and specified time t.
1. Determine the creep limit using the creep rate. 2. Determine the creep limit using the total elongation
The creep limit is the maximum constant stress at which the creep deformation or creep rate of the specimen, under specified temperature and time conditions, does not exceed a specified value. It has two ways of representation: ① expressed using, where t is the test temperature (°C), τ is the test time (hours), and δ is the specified creep deformation amount (%). For example, =150 MPa means that the creep limit of a certain material is 150 MPa when the temperature is 600°C, the testing time is 100,000 hours, and the total creep deformation is 1%. ②Expressed in symbols, where t is the test temperature (°C) and v is the creep rate in the second stage of creep (%/hour). For example, =100 MPa means that the creep limit of a certain material at a temperature of 700°C and a creep rate of (1/105)%/hour is 100 MPa. The tensile creep testing method involves: at a constant temperature, placing a set of specimens under different constant stresses to conduct tests, thereby obtaining a series of creep curves; subsequently, a graph showing the relationship between creep rate and stress at that temperature is drawn on a double logarithmic scale, and from this graph the creep limit at a specified creep rate can be determined.