Astm D7791 Test Methods
Procedure A Tension Fatigue Tests
A rectangular or circular cross section test specimen is cyclically loaded in tension to a specific stress or strain level at a selected frequency until the specimen fails. Fatigue strengths are determined at specific cycle counts. Four different stress or strain levels are tested to construct a stress versus number of cycles to failure curve or a strain versus number of cycles to failure to determine the endurance limit of the material in tension. Specimen dimensions, shape, surface conditions, and limitations need to match ASTM D638.
Procedure B Compression Fatigue of Rigid Plastics
A rectangular or circular cross section test specimen is cyclically loaded in compression to a specific stress or strain level at a selected frequency until the specimen fails. Fatigue strengths are determined at specific cycle counts. Four different stress or strain levels are tested to construct a stress versus number of cycles to failure curve or a strain versus number of cycles to failure to failure to determine the endurance limit of the material in compression. Specimen dimensions, shape, surface conditions, and limitations need to match ASTM D695. An anti buckling fixture may be used.
Astm D7791 Uniaxial Fatigue Testing Of Plastics
ASTM D7791 describes how to determine the dynamic fatigue properties of plastics in uniaxial loading.
If you plan on conducting ASTM D7791 we recommend acquiring the test standard from ASTM. There are many important details regarding this test method that are provided which are key to achieving successful results. Every standard provides important environmental conditions, test sample preparation and conditioning requirements, sample dimensions and test reporting expectations. Its critical that you fully understand the standard so that you can set up the test, run the procedure, and report the results requirements.
Astm D7774 Test Methods
Procedure A Three Point Flexural Fatigue Test Specimen dimensions, shape, surfaces, and limitations are in compliance with Test Method ASTM D790.
Procedure B Four Point Flexural Fatigue Test Specimen dimensions, shape, surfaces, and limitations are in compliance with Test Method ASTM D6272. The test method only covers specimens with 1:2 or 1:3 load span-to-support span ratios.
Specimens are cyclically loaded equally in the positive and negative directions to specific stress or strain level at a uniform frequency until the specimen ruptures or yields.
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Astm E466 Metallic Materials Fatigue Testing
ASTM E466 | Metallic Materials | Fatigue Testing
ASTM E466 describes the determination of the fatigue strength of metallic materials in the fatigue regime where the strains are predominately elastic, both upon initial loading and throughout the test. This test method is applicable for axial unnotched and notched specimens subjected to constant amplitude, periodic force.
Before conducting ASTM E466, it is important to read the entire specification in the relevant ASTM publication.
ASTM E466 | Metallic Materials | Fatigue Testing
What Is Fatigue Testing
Fatigue testing is a specialized mechanical test performed by using test machines capable of applying cyclic loads to simulate real-life challenges that materials may encounter.
Strain-controlled fatigue testing methods are influenced by the same variables that influence force-controlled fatigue.
It is a type of test that is used to generate fatigue-life data to identify critical locations or demonstrate the safety of a structure that could be susceptible to fatigue.
Methods for fatigue testing are utilized to characterize material properties and/or component behavior during the fatigue testing procedure. The test utilizes cyclic loading to predict the life expectancy of material components and how it can react in real-world situations.
Determining the component properties helps prevent failures in a number of industries, including aerospace, oil and gas, and the medical industry.
Our fatigue testing procedure is one of the most crucial elements of research and development, product safety, and material component verification programs.
Fatigue testing utilizes cyclic loading to predict the life expectancy of material components and how it can react in real-world situations.
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Mini Fatigue Testing Results
Fatigue testing was performed per ASTM E 466 and reported per ASTM E 468 . In this work, fatigue tests were performed on the base material, FSP material with two different tool designs, GMAW material, formed base material, formed FSP material, FSW material by using mini fatigue samples under completely reversed flexure .
Figure 4.113. Mini fatigue specimens used in this study.
Table 4.3. Summary of Yield Stress, Applied Stress, Amplitude Values, and Corresponding Fatigue Life of Each Material
| Sample |
|---|
Importance Of The Fatigue Testing Procedure
Fatigue testing measures how cyclic forces will impact a product or material over the course of time.
Using varying loads, speeds, and environmental conditions to monitor material behavior, fatigue testing machines simulate real-world behaviors and scenarios.
In many applications, materials are subjected to oscillating forces. The materials tested behave differently under these conditions as compared to a static load.
Because of this, engineers are faced with predicting the fatigue life of the material. Fatigue life can be defined as the total number of cycles to failure under specified loading conditions.
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Important Considerations When Testing Per Astm D7791
Testing is needed because not all plastics have the same material response to fatigue. If a plastic does not have an elastic range, it will cause the amplitude of the programmed load or deformation to change during testing. This can happen as a result of fatigue testing and cause plastic deformation. Caution should be taken when using the results for design as they are generally not indicative of the true fatigue properties of the material.
The results of tests are suitable for application in design only when the specimen test conditions realistically simulate the actual service conditions.
Test To Success Methodology
Historically, fatigue resistance for cardiovascular devices has been evaluated by the test to success strategy. This means most cardiac and intravascular implants are subjected to 400 or 600 million cycles of durability testing without any observations of fracture in order to mimic a service life of 10 or 15 years, respectively. Devices such as vena cava filters, which undergo respiratory loading, are tested to 100 million cycles and superficial femoral artery devices, subject to gait motion loading, are typically tested to 10 million cycles to simulate 10 years of service life.
If a device is loaded to physiologically-relevant conditions that mimic the expected service life without failure, the test is considered successful. Testing to success essentially provides a minimum verification of the performance of the device.
Using the Bayes Success Run Theorem, 29 to 59 non-fractured samples are required for 90% or 95% reliability and 95% confidence level. To raise reliability to 99%, 299 defect-free samples would be required, which is a deterrent with both time and investment. Device manufacturers make the reliability target determination based on device risk and regulatory guidance, but it is most common to see sample sizes of 29 test specimens for these configurations. Abbreviated studies sometimes will contain 6, 12, or 15 samples.
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Standardized Fatigue Testing Specifications
- ASTM E399: Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIC of Metallic materials
- ASTM E466: Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials
- ASTM E468: Standard Practice for Standard Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic Materials
- ASTM E606: Standard Practice for Strain-Controlled Fatigue
- ASTM F1160: Standard Test Method for Shear and Bending Fatigue Testing of Calcium Phosphate and Metallic Medical Coatings
- ASTM F1440: Standard Practice for Cyclic Fatigue Testing of Metallic Stemmed Hip Arthroplasty Femoral Components without Torsion
- ASTM F1612: Standard Practice for Cyclic Fatigue Testing of Metallic Stemmed Hip Arthroplasty Femoral Components with Torsion
- ASTM F1800: Standard Test Method for Cyclic Fatigue Testing of Metal Tibial Tray Components of Total Knee Joint Replacements
Important Considerations When Testing Per Astm D7774
Testing is needed because material response in fatigue is not identical for all plastics. If a plastic does not exhibit an elastic region, where strain is reversible, plastic deformation will occur during fatigue testing, causing the amplitude of the programmed load or deformation to change during testing. Caution shall be taken when using the results for design as they are generally not indicative of the true fatigue properties of the material.
The results of tests are suitable for application in design only when the specimen test conditions realistically simulate the actual service conditions.
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Guide For Fatigue Testing And Statistical Analysis
About 15 years ago, ASTM Committee E-9 on Fatigue prepared a Manual on Fatigue Testing. That Manual attempted to standardize the symbols and nomenclature used in fatigue testing, described the principal types of testing machines then in use, presented detailed instructions for the preparation of test specimens, outlined test procedures and techniques, and gave some suggestions for the presentation and interpretation of fatigue data. Since the Manual was first prepared, a number of new techniques have been developed for evaluating the fatigue properties of materials. Furthermore, the application of statistical methods to the analysis of the test results of samples offers a means for estimating the characteristics of the population from which the samples were taken. To take cognizance of these developments, this guide has been prepared.
Dynamic Test Machines For Astm D7774
Our 800 series fatigue test machines serve both static and fatigue testing applications. The 800 series is capable of performing plastics fatigue tests at speeds up to 15 hz with load capacities up to 50 kN . They feature all electric dynamic actuators. All of our fatigue testers are capable of load, strain and position control.
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What Is Astm D7791
The ASTM D7791 standard is a test for tension-tension fatigue in plastics. ASTM D7791 applies to rigid and semi-rigid plastics. Uniaxial tension and compression fatigue test machines are employed to create stress and strain levels below the proportional limits of the material where the strains and stresses are relatively elastic.
Standard Practice For Corrosion Fatigue Testing Of Metallic Implant Materials
1.1 This practice covers the procedure for performing corrosion fatigue tests to obtain S-N fatigue curves or statistically derived fatigue strength values, or both, for metallic implant materials. This practice describes the testing of axially loaded fatigue specimens subjected to a constant amplitude, periodic forcing function in saline solution at 37°C and in air at room temperature. The environmental test method for implant materials may be adapted to other modes of fatigue loading such as bending or torsion. While this practice is not intended to apply to fatigue tests on implantable components or devices, it does provide guidelines for fatigue tests with standard specimens in an environment related to physiological conditions.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
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How Is Fatigue Testing Performed
Fatigue testing is typically performed using servo-hydraulic testing machines.
While a portion of fatigue tests are performed to plot stress against the number of cycles it takes for the item or material to fail, fatigue tests can also be used to simulate specific scenarios to assist with investigating real-world failures.
Scenarios include, but are not limited to, testing engine airfoil and gas turbine components to determine the expected life of the material.
ITS has more than 30 digitally controlled servo-hydraulic test frames. Our frames are outfitted with a state-of-the-art fixturing and data acquisition systems.
We customize methodologies and procedures for each specific product and material to ensure the highest-quality result is achieved.
Customizable Fatigue Testing Capabilities
Westmoreland Mechanical Testing & Researchs substantial onsite capabilities allow us to customize each project to your materials and mechanical specifications. Westmoreland Mechanical Testing & Research provides unique customer advantages in fatigue testing, including custom analyzation, superior turnaround time, and an extensive scope of fatigue testing:
- Custom Analyzation – We design and write proprietary software to analyze your test results.
- Superior Turnaround Time – To ensure the best turnaround time on your projects, we design and machine specialized fixtures.
- Customizable, Extensive Scope For your unique testing needs we have the resources, experience, and testing capacity to get the job done right.
- Experts in Fatigue – We are specialists in conducting axial tests on many different types of specimens.
These tests conduct load, strain, or position control on servo-hydraulic test equipment at temperatures ranging from Cryogenic to over 2400°F. We have the flexibility and resources to accommodate a wide variety of sample sizes with our machine capacity ranging from 25grams to 1,000,000lbs.
WMT& R is an industry leader in Low Cycle Fatigue and High Cycle Fatigue Testing for the automotive, aeronautic, motorsport, marine, ministry of defense, manufacturing and power generation industries.
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Loading In The Low Cycle Fatigue Test
Loading in low cycle fatigue tests comprises an elastic a,e and a plastic a,p strain proportion: a,t = a,e + a,p
While a linear relationship exists between stress and strain in the elastic range , this relationship is non-linear in the plastic range. This results in a hysteresis loop.
Low cycle fatigue tests to ISO 12106 / ASTM E606 are run at constant amplitude. In addition, hold times can be introduced to examine creep/relaxation processes. A triangular waveform is used as set value, or a trapezoidal wave for hold times.
If specific operating loads are to be simulated, other strain-time sequences are also possible. Thus low cycle fatigue tests are also performed with a superimposed higher-frequency oscillation.
The test frequency is usually lower than / equal to 1 Hz, although this limit is constantly shifting upwards with the result that LCF tests are being performed at up to 10 Hz.
Strain control is used for these LCF tests. Only in special cases is there a change to force-control in the stabilized hysteresis range or for hold times in order to investigate creep tests. For materials characterization, the tests are usually performed at an R ratio of -1.
Fatigue Standards And Fracture Standards
ASTM’s fatigue and fracture standards provide the appropriate procedures for carrying out fatigue, fracture, and other related tests on specified materials. These tests are conducted to examine and evaluate the behavior, susceptibility, and extent of resistance of certain materials to sharp-notch tension, tear, axial fatigue, strain-controlled fatigue, surface crack tension, creep crack, and residual strain. In addition to fracture toughness and strain gradient, these standards also present the procedures for determining K-R curves, stress-life and strain-life fatigue data, threshold stress intensity factors, and reference temperatures. These fatigue and fracture standards are useful to manufacturers and other users concerned with such materials in understanding their failure and stability mechanisms.
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Advanced Apparatus and Techniques
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Fatigue Testing Of Composites
Fatigue testing may be performed at multiple points during the design of a composite structure. A focus on small-specimen level fatigue test methods, however, suggests a need for more testing method standardization.
Fig. 1. Standard method used for displaying fatigue test results. 1a shows standard fatigue testing terminology, and 1b. depicts an S-N diagram. Photo Credit: Dan Adams
Fatigue testing may be performed at multiple points during the design of a composite structure. A focus on small-specimen level fatigue test methods, however, suggests a need for continued test method standardization.
Fatigue testing involves the application of cyclic loading to a test specimen or a structure. Unlike monotonic tests in which loading increases until failure, the applied load is cycled between prescribed maximum and minimum levels until a fatigue failure occurs, or until the predetermined number of loading cycles have been applied.If failure does not occur within the prescribed number of loading cycles ranging from thousands to millions depending on the application of interest the test result is referred to as a run-out.
Astm D7774 Flexural Fatigue Testing Of Plastics
ASTM D7774 describes how to measure the full reversed fatigue properties of plastics in flexure, and applies to both rigid and semi-rigid plastics. Stress and strain levels are below the proportional limit of the plastic where the strains and stresses are relatively elastic. Both three and four point bend fixtures are used for the tests.
If you plan on conducting ASTM D7774 we recommend acquiring the test standard from ASTM. There are many important details regarding this test method that are provided which are key to achieving successful results. Every standard provides important environmental conditions, test sample preparation and conditioning requirements, sample dimensions and test reporting expectations. Its critical that you fully understand the standard so that you can set up the test, run the procedure, and report the results requirements.
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