Method for rapid testing of intermittent loading sensitivity of creep properties of metallic materials
By conducting continuous and intermittent loading tests on the same specimen, combined with the quantitative evaluation of the creep strain rate ratio, the test error caused by specimen differences in the prior art is solved, and a rapid and accurate evaluation of the intermittent loading sensitivity of the creep properties of metallic materials is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA STATE SHIPBUILDING CORP LTD RESEARCH INSTITUTE 719
- Filing Date
- 2026-03-19
- Publication Date
- 2026-05-29
AI Technical Summary
In the existing technology, it is difficult to accurately reflect the intermittent loading sensitivity of the creep properties of metallic materials by performing continuous loading and intermittent loading separately, and there are test errors caused by differences between samples.
By employing a continuous loading and intermittent loading continuous testing method on the same specimen, and combining continuous loading and intermittent loading creep tests on the same specimen with a quantitative evaluation method of creep strain-creep time curve and creep strain rate ratio, the differences between specimens are eliminated, and a rapid and accurate evaluation of material creep performance is achieved.
It significantly improves the accuracy and reliability of the test. Through the continuous loading mode of "continuous first, then intermittent", the test can be completed in a short time, realizing efficient, objective and quantitative determination of the sensitivity of materials to intermittent loading.
Smart Images
Figure CN122108765A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of materials and parts testing technology, specifically relating to a rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials. Background Technology
[0002] Current stress loading techniques typically separate continuous and intermittent loading, using either either method. However, many components do not experience continuous loads throughout their service life. For components that creep under non-continuous loads, the impact of intermittent loading on their creep deformation needs to be considered. Due to differences between specimens, comparing individual specimen test results often fails to accurately reflect the intermittent loading sensitivity of material creep properties. For example, performing a "continuous tension" test on rubber band A and an "intermittent tension" test on rubber band B, and then comparing the results, is unlikely to accurately reflect the intermittent loading sensitivity of material creep properties. This is because due to inhomogeneities and differences in microstructure, rubber bands A and B may have different properties; for instance, one may contain microscopic defects, while the other may have none or almost none. It's impossible to determine whether the difference in the final results is due to the "different loading methods" or the "differences in the rubber bands themselves." Summary of the Invention
[0003] This invention proposes a rapid testing method for the intermittent loading sensitivity of creep properties in metallic materials. The aim is to address the problem that when comparing results from separate continuous and intermittent loading tests, the differences between samples often make it difficult to accurately reflect the intermittent loading sensitivity of material creep properties.
[0004] To solve its technical problem, the present invention adopts the following technical solution: A rapid test method for the intermittent loading sensitivity of creep properties in metallic materials, characterized by the following steps: Step 1: Select the creep specimen to be tested and conduct a continuous loading creep test on a creep testing machine that meets the test conditions. The cumulative creep time under continuous loading shall not be less than a set time or not exceed a set time range. The set time or set time range can balance test efficiency and data reliability. Step 2: Keep the creep stress constant and change the continuous loading creep mode to intermittent loading creep mode. The cumulative creep time of this intermittent loading should not be less than a set time or not exceed a set time range. This set time or set time range can balance test efficiency and data reliability. Step 3: Obtain creep strain-creep time data under different loading conditions and plot creep strain-creep time curves.
[0005] Step 4: Determine the creep performance sensitivity of the material under test under creep stress and intermittent loading within the range of intermittent time based on the creep strain-creep time curve; establish a quantitative evaluation method based on creep strain rate and creep strain rate ratio.
[0006] Furthermore, the ratio of the continuous loading cumulative creep time to the intermittent loading cumulative creep time is 1:1.
[0007] Furthermore, the cumulative creep time of continuous or intermittent loading in steps one and two is not less than a set time, including not less than 50 hours; the cumulative creep time of continuous or intermittent loading in steps one and two is not less than a set time range, including not more than 30 hours to 100 hours.
[0008] Furthermore, the continuous loading creep test and the intermittent loading creep test are conducted using the same specimen to eliminate the influence of differences between specimens.
[0009] Furthermore, the cumulative creep time of intermittent loading is achieved through multiple cycles, with each cycle including loading, unloading, and holding time of no less than 1 hour.
[0010] Furthermore, the quantitative evaluation method based on creep strain rate established in step four compares the creep strain rates of continuous loading and intermittent loading to determine the material's sensitivity to intermittent loading.
[0011] Furthermore, the quantitative evaluation method established in step four based on the creep strain rate ratio... Law That is, to calculate the ratio of creep strain rate under continuous loading to that under intermittent loading, and to determine the sensitivity of the material to intermittent loading when the ratio exceeds a preset threshold.
[0012] Furthermore, when switching from continuous loading to intermittent loading, the load is unloaded to a set stress value and held for a set time to maintain stable contact between the specimen and the fixture and prevent loosening. Advantages and effects of the present invention
[0013] This invention provides a rapid testing method for the intermittent loading sensitivity of creep properties in metallic materials. Its core advantage lies in the fact that by continuously performing both continuous and intermittent loading tests on the same sample, the influence of sample differences is fundamentally eliminated, significantly improving testing accuracy and reliability. This method employs a continuous loading mode of "continuous first, then intermittent," enabling testing to be completed in a shorter time, effectively improving efficiency. Simultaneously, by quantitatively evaluating the creep strain rate and creep strain rate ratio and comparing them with preset thresholds, an objective and quantitative determination of the material's intermittent loading sensitivity is achieved. Furthermore, by precisely controlling the cumulative creep time and loading cycle, testing efficiency and accuracy are balanced. This invention solves the problems of test separation and low efficiency in existing technologies, achieving a rapid, accurate, and objective assessment of the intermittent loading sensitivity of material creep properties. Attached Figure Description
[0014] Figure 1 These are schematic diagrams illustrating different loading modes of the present invention. a: Continuous loading creep; b: Intermittent loading creep; Figure 2 This is a schematic diagram showing the shape and dimensions (unit: mm) of the Ti80 titanium alloy compression creep specimen of the present invention. Figure 3 The figures show the compressive creep strain-creep time curves of Ti80 titanium alloy under different loading modes at a compressive creep stress of 767 MPa according to the present invention. Figure 4 This is a flowchart of a rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to the present invention. Detailed Implementation Innovation of this invention
[0015] 1. Continuous Testing Method Using the Same Specimen Under Continuous and Intermittent Loading: Unlike existing technologies that require multiple specimens for continuous and intermittent loading creep tests, this invention creatively uses the same specimen to conduct continuous and intermittent loading creep tests sequentially. This method fundamentally eliminates testing errors caused by inherent differences between different specimens, significantly improving the accuracy and reliability of test results.
[0016] 2. Rapid measurement is achieved: Through the continuous loading mode of "continuous first, then intermittent", the sensitivity of metallic materials to intermittent loading can be measured efficiently and quickly, effectively improving the testing efficiency.
[0017] 3. A quantitative criterion for intermittent loading sensitivity was established: This invention proposes a quantitative evaluation method based on creep strain rate and creep strain rate ratio by comparing and analyzing the creep strain-time curves of the same sample under continuous and intermittent loading conditions. By comparing the calculation results with a preset threshold, the sensitivity of the material to intermittent loading can be objectively and quantitatively determined, providing a clear basis for material performance evaluation. Design principle of the invention
[0018] This invention abandons the traditional "group comparison" approach and innovatively proposes an experimental method of "time-series comparison of the same sample". Its core design principle is as follows: 1. Ultimate Application of the Controlled Variable Method: The core idea of this invention is to control variables other than the loading method to the greatest extent possible. Specifically, by conducting continuous loading and intermittent loading creep tests on the same specimen, it is ensured that all intrinsic properties of the specimen, such as material composition, microstructure, and initial state, are completely consistent.
[0019] 2. Elimination of individual variability interference: This method fundamentally eliminates the biggest source of error—"individual variability between samples." Any observed differences in creep behavior can be attributed to changes in the loading regime (from continuous to intermittent), thus achieving high-precision and high-reliability assessment of sensitivity to intermittent loading.
[0020] 3. Innovative test sequence design: The key is the "continuous loading followed by intermittent loading" test sequence. First, the creep behavior of the specimen under reference conditions is obtained through a continuous loading phase. Then, without replacing the specimen, the test is switched to an intermittent loading mode. By comparing the creep curves, creep strain rates, and creep strain rate ratios of the same specimen in the two phases, the effect of intermittent loading can be directly and clearly quantified.
[0021] 4. Design Summary: The design principle can be concisely summarized as follows: Through the innovative experimental design of "same sample, time sequence comparison", the precise isolation and examination of the single variable "intermittent loading" is achieved, thereby overcoming the problems of inaccurate evaluation caused by individual sample testing and individual sample differences in traditional methods, and providing a more scientific and reliable testing and evaluation method for the intermittent loading sensitivity of material creep properties.
[0022] Based on the above principles, this invention designs a rapid testing method for the intermittent loading sensitivity of creep properties in metallic materials, as follows: Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown, its characteristics include the following steps: Step 1: Select the creep specimen to be tested and conduct a continuous loading creep test on a creep testing machine that meets the test conditions. The cumulative creep time under continuous loading shall not be less than a set time or not exceed a set time range. The set time or set time range can balance test efficiency and data reliability. Step 2: Keep the creep stress constant and change the continuous loading creep mode to intermittent loading creep mode. The cumulative creep time of this intermittent loading should not be less than a set time or not exceed a set time range. This set time or set time range can balance test efficiency and data reliability. Step 3: Obtain creep strain-creep time data under different loading conditions and plot creep strain-creep time curves.
[0023] Step 4: Determine the creep performance sensitivity of the material under test under creep stress and intermittent loading within the range of intermittent time based on the creep strain-creep time curve; establish a quantitative evaluation method based on creep strain rate and creep strain rate ratio.
[0024] Furthermore, the ratio of the continuous loading cumulative creep time to the intermittent loading cumulative creep time is 1:1.
[0025] Furthermore, the cumulative creep time of continuous or intermittent loading in steps one and two is not less than a set time, including not less than 50 hours; the cumulative creep time of continuous or intermittent loading in steps one and two is not less than a set time range, including not more than 30 hours to 100 hours.
[0026] Supplementary Note 1: The aforementioned "set time" and "set time range" aim to address the problem of how to capture the key creep characteristics of materials.
[0027] ① Setting a lower limit (e.g., ≥30 or 50 h): To obtain significant creep curve characteristics and ensure data comparability. Too short a timeframe will result in indistinct creep curve characteristics under different loading conditions, hindering comparison and analysis. ② Setting an upper limit (e.g., ≤100 h): To ensure the method's "practicality": A. Controlling cost and time: If a test claims to evaluate long-term performance but requires thousands of hours to complete, its application value will be greatly reduced. B. This invention aims to accurately measure the sensitivity to intermittent loading through a relatively short and efficient test. Excessively long test times may enter the accelerated creep phase, making it impossible to obtain effective comparative data. C. A range of "30-100 h" or similar, rather than a fixed value, gives this method broad applicability. Researchers can choose an appropriate duration within this validated range based on their research needs.
[0028] Supplementary Note 2: The aforementioned "using the same sample" addresses the challenge of "sample variability." In traditional methods, comparing results using different samples is susceptible to the influence of material inhomogeneities. This invention, by testing with the same sample, reduces influencing factors and improves accuracy. This point was easily overlooked in early studies because researchers often assumed sample uniformity; however, differences in material microstructure can lead to significant deviations in data.
[0029] Furthermore, the cumulative creep time of intermittent loading is achieved through multiple cycles, with each cycle including loading, unloading, and holding time of no less than 1 hour.
[0030] Furthermore, the quantitative evaluation method based on creep strain rate established in step four compares the creep strain rates of continuous loading and intermittent loading to determine the material's sensitivity to intermittent loading.
[0031] Supplementary Note 3: The creep strain rate described above focuses on the rate of creep deformation at a given instant, much like the speedometer reading at a given moment. Car A travels at 100 km / h, and car B travels at 90 km / h. Its significance in materials science lies in its role as a crucial parameter for studying the creep behavior of materials. By analyzing changes in the creep strain rate, we can determine the material's sensitivity to intermittent loading.
[0032] Furthermore, the quantitative evaluation method established in step four based on the creep strain rate ratio... Law That is, to calculate the ratio of creep strain rate under continuous loading to that under intermittent loading, and to determine the sensitivity of the material to intermittent loading when the ratio exceeds a preset threshold.
[0033] 2) Creep strain rate ratio: This is a relative indicator that directly compares the ratio of creep deformation rate before and after changing the loading mode under two different loading conditions. It doesn't look at the absolute value of the rate, but rather calculates the ratio. If the ratio is close to 1, it means the material's creep deformation rate is similar regardless of whether it's under continuous or intermittent stress. If the ratio is greater than 1 or less than 1, it means the loading method affects the material's creep deformation rate, and the material is sensitive to intermittent loading. This is crucial for evaluating the creep performance of materials under real-world (often intermittent) working conditions.
[0034] Supplementary Note 4: The relationship and workflow between the above-mentioned creep strain rate and creep strain rate ratio are as follows: Step 1: Measuring basic data: Through experiments, two curves were obtained: one is the "creep strain-creep time" curve under continuous loading, and the other is the curve under intermittent loading; Step 2: Calculate the creep strain rate: Calculate the creep strain rate at different times from the two curves using mathematical methods (such as differentiation or piecewise calculation). Step 3: Calculate the "creep strain rate ratio": Compare instantaneous sensitivity (look at the rate ratio): At a specific time point, such as after the end of continuous loading and the start of intermittent loading, divide the two creep strain rates calculated in Step 2 to obtain the creep strain rate ratio. This clarifies: "Which loading method results in faster creep deformation?"
[0035] Furthermore, when switching from continuous loading to intermittent loading, the load is unloaded to a set stress value and held for a set time to maintain stable contact between the specimen and the fixture and prevent loosening. Example 1
[0036] The following tests were conducted on Ti80 titanium alloy at a compressive creep stress of 767 MPa and... Figure 1 The creep performance sensitivity under the shown loading mode is illustrated using intermittent loading as an example for detailed explanation.
[0037] First, the design of continuous loading: First, select an item such as... Figure 2 The compression creep specimen shown was tested using a creep testing machine at a compressive creep stress of 767 MPa according to... Figure 1 (a) A continuous loading creep test was performed for 100 h in loading mode. Then, the compressive load was unloaded to 500 N and held for 3 s to maintain stable contact between the specimen and the fixture and prevent loosening.
[0038] The reason for choosing a high stress of 767 MPa is that creep is significant at high temperatures, but at room temperature, higher stresses are usually required to observe it. Such a high stress level is chosen to induce sufficiently significant and measurable creep deformation within a reasonable test time (100 h rather than thousands of hours), thus making the difference between the two loading modes clearly visible.
[0039] Second, the intermittent loading design: The compressive load is then applied to a compressive creep stress of 767 MPa and maintained for 1 hour. The unloading and loading times are both 2 minutes. The loading method is as follows: Figure 1 As shown in (b). This process was repeated until the cumulative compression creep time under intermittent loading reached 100 h. Throughout the entire test, the deformation of the test section of the specimen was recorded using an extensometer.
[0040] The obtained Ti80 compression creep strain-creep time curves under different loading conditions are as follows: Figure 3 As shown. From Figure 3It can be seen that when the continuous loading creep mode is changed to intermittent loading creep mode, the rate of change of compressive creep strain of Ti80 titanium alloy with creep time is significantly larger, and intermittent loading promotes the accumulation of compressive creep strain of Ti80 titanium alloy. Figure 3 The change in the compressive creep strain-creep time curve trend reflects the difference in compressive creep properties of Ti80 titanium alloy under continuous loading and intermittent loading, that is, the compressive creep properties of Ti80 titanium alloy at a compressive creep stress of 767 MPa. Figure 1 The loading mode shown exhibits significant intermittent loading sensitivity.
[0041] Summary: By comparing the results of intermittent loading and continuous loading creep tests (continuous loading at 767 MPa for 100 h), the influence of periodic unloading on the creep behavior of materials was studied, i.e., the "intermittent loading sensitivity" of materials was evaluated.
[0042] Third, the function of the residual load (500 N): A. To ensure that the test fixture and the specimen remain in contact and clamped at all times, avoiding loosening, gaps, or re-alignment problems caused by complete unloading. B. To enable measurement systems such as extensometers to work continuously and obtain consistent and accurate deformation data. If completely unloaded, the measurement reference may drift.
[0043] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.
Claims
1. A rapid test method for the intermittent loading sensitivity of creep properties in metallic materials, characterized in that, Includes the following steps: Step 1: Select the creep specimen to be tested and conduct a continuous loading creep test on a creep testing machine that meets the test conditions. The cumulative creep time under continuous loading shall not be less than a set time or not exceed a set time range. The set time or set time range can balance test efficiency and data reliability. Step 2: Keep the creep stress constant and change the continuous loading creep mode to intermittent loading creep mode. The cumulative creep time of this intermittent loading should not be less than a set time or not exceed a set time range. This set time or set time range can balance test efficiency and data reliability. Step 3: Obtain creep strain-creep time data under different loading conditions and plot creep strain-creep time curves; Step 4: Determine the creep performance sensitivity of the material under test under creep stress and intermittent loading within the intermittent time range based on the creep strain-creep time curve, and establish a quantitative evaluation method based on creep strain rate and creep strain rate ratio.
2. The rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to claim 1, characterized in that, The ratio of the cumulative creep time under continuous loading to the cumulative creep time under intermittent loading is 1:
1.
3. The rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to claim 1, characterized in that, The cumulative creep time of continuous or intermittent loading in steps one and two shall not be less than a set time, including not less than 50 hours; the cumulative creep time of continuous or intermittent loading in steps one and two shall not be less than a set time range, including not more than 30 hours to 100 hours.
4. The rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to claim 1, characterized in that, The continuous loading creep test and the intermittent loading creep test were conducted using the same specimen to eliminate the influence of differences between specimens.
5. The rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to claim 1, characterized in that, The cumulative creep time of intermittent loading is achieved through multiple cycles, with each cycle including loading, unloading, and holding time of no less than 1 hour.
6. The rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to claim 1, characterized in that, The establishment of a quantitative evaluation method based on creep strain rate in step four involves comparing the creep strain rates under continuous loading and intermittent loading to determine the material's sensitivity to intermittent loading.
7. The rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to claim 1, characterized in that, The fourth step, establishing a quantitative evaluation method based on the creep strain rate ratio, involves calculating the creep strain rate ratio under continuous loading and intermittent loading. When the ratio exceeds a preset threshold, the sensitivity of the material to intermittent loading is determined.
8. The rapid testing method for the intermittent loading sensitivity of creep properties of metallic materials according to claim 1, characterized in that, When switching from continuous loading to intermittent loading, the load is unloaded to a set stress value and held for a set time to maintain stable contact between the specimen and the fixture and prevent loosening.