Astm Fatigue Testing Standards
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Test To Success & Astm F3211 Fatigue To Fracture Methodologies
Testing to success or testing to failure using Fatigue to Fracture – does one method provide more insights into cardiovascular device performance than the other?
Industries such as Aerospace and Transportation predominantly test fatigue under a range of conditions so that they can predict fatigue life behavior based on design characteristics and material properties. In the medical industry, fatigue life analysis through fatigue to fracture hasnt been used quite as often. The material properties of the common medical materials are established, but it is becoming more frequently used alongside the test to success method to characterize design performance.
The standard methodology for fatigue to fracture testing, ASTM F3211, was developed in response to the increase in utilizing FtF testing to help model failure methods and limits for cardiovascular implants. Prior to its release, a standard method for cardiovascular device testing was not readily available.
In this article, we review the test to success and fatigue to fracture methodologies, their differences, and how they are critical in evaluating the durability of stents, heart valves, occluders, and other cardiovascular devices for safety and regulatory approval.
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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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
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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Standard Guide For Fretting Fatigue Testing
| fretting fatigue slip sliding |
1.1 This guide defines terminology and covers general requirements for conducting fretting fatigue tests and reporting the results. It describes the general types of fretting fatigue tests and provides some suggestions on developing and conducting fretting fatigue test programs.
1.2 Fretting fatigue tests are designed to determine the effects of mechanical and environmental parameters on the fretting fatigue behavior of metallic materials. This guide is not intended to establish preference of one apparatus or specimen design over others, but will establish guidelines for adherence in the design, calibration, and use of fretting fatigue apparatus and recommend the means to collect, record, and reporting of the data.
1.3 The number of cycles to form a fretting fatigue crack is dependent on both the material of the fatigue specimen and fretting pad, the geometry of contact between the two, and the method by which the loading and displacement are imposed. Similar to wear behavior of materials, it is important to consider fretting fatigue as a system response, instead of a material response. Because of this dependency on the configuration of the system, quantifiable comparisons of various material combinations should be based on tests using similar fretting fatigue configurations and material couples.
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.
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New Astm Standard On Creep
Creep-fatigue testing simulates the loading and temperature conditions experienced by turbine components of aircraft engines, nuclear reactor components and fossil power plant components during service. With increasing need for cyclic operation during peak power demands, reliable creep-fatigue test data is necessary for the life assessment of aging power plants.
A new ASTM standard, ASTM E2714, Test Method for Creep-Fatigue Testing, provides a means for this type of testing. The new standard was developed by Subcommittee E08.05 on Cyclic Deformation and Fatigue Crack Formation, part of ASTM International Committee E08 on Fatigue and Fracture.
According to Ashok Saxena, Ph.D., dean, distinguished professor and Irma and Raymond Giffels Endowed Chair, College of Engineering, University of Arkansas, test results from the standard can be used to assess the suitability of materials for demanding applications in which safety is a primary concern.
The results are also used to predict the design and remaining life of components that operate at high temperatures and to determining how frequently these components must be inspected for damage in the form of cracks during services, says Saxena, one of the co-chairs of the task group that developed E2714.
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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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Low Cycle Fatigue Test Procedure
Following careful installation, the specimen is heated to the test temperature. For this the machine is in force-control mode, with set value of 0 kN. Once the required temperature has been reached, the extensometer is attached. If the extensometer was already on the specimen during the heating phase, allowance must be given for a change in L0. Strain control is now selected and the test started.
The initial cycles are of particular importance as materials may display strongly differing behavior at this point.
However, a stabilized hysteresis is generally established after a number of cycles. There are also many materials which exhibit neither hardening nor softening
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
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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.
Ultrasonic Fatigue Test System
High frequency fatigue testing can be performed by use of such a test system that involves cyclic loading of a test sample at frequencies in the range of 10 to 25 kHz. The principal advantage of using an ultrasonic fatigue test system is greater reduction of time in characterizing the fatigue limit. It consists of a sonic energy converter, a series of acoustic amplifying horns, computerized test control system, test specimen, a cycle-counter, test frequency display, and temperature. More details on ultrasonic fatigue test system and their use for a variety of fatigue testing may be found in the handbook of the American Society for Metals . The basic ultrasonic fatigue system is suitable for generation of material stresslife data and fatigue crack growth, rate data for metals, composites, ceramics, glass and plastics within a short time.
Douglas Thorby, in, 2008
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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.
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.
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Fatigue To Fracture Methodology
Fatigue is a progressive weakening or cumulative occurrence of localized permanent deformation due to cyclic loading. Fatigue to Fracture testing provides data about a material or devices failure modes and fatigue behavior, which is critical information for preventing adverse conditions like radial support loss, thrombus formation, or perforation of the vessels. FtF testing applies controlled loads or strains at a variety of levels above those used for test to success evaluation. These hyper-physiological tests are intended to predict the devices fatigue life by causing fracture. Observing fracture progression and location improves understanding of the structural impact caused by different types of fractures.
Before FtF testing, Finite Element Analysis can be used to determine the type of test sample , worst-case and failure test conditions, and several other performance characteristics. While these computational models evaluate the stresses and strains on the tested systems, the models need to be validated with experimental data to ensure the predicted results align with benchtop results. Mechanical properties are imported into the models and then fatigue to fracture testing yields defined failure points for model comparison. Two key guidance documents for FEA simulation are ASTM F2514, Standard Guide for Finite Element Analysis of Metallic Vascular Stents Subjected to Uniform Radial Loading, and ASME V& V40.
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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Dynamic Test Machines For Astm D7791
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 . The 800 series is based on all electric dynamic actuators. All of our fatigue testers are capable of load, strain and position control.
