We perform cryogenic testing in liquid nitrogen from 10 kip to kip. Advanced techniques such as crack opening load measurement, Adjusted Compliance Ratio ACR and constant K max testing are used to measure and account for crack closure. LTI is also equipped to test small cracks using the KB type surface flaw specimen. Test specimens can be machined in all standard geometries.
Compact Tension C T and Middle Tension M T specimen configurations in a range of sizes are commonly used for fatigue crack growth analysis. Cracking can be caused by any one or a combination of factors, such as manufacturing defects and the use of inadequate materials. Businesses often turn to third-party testing labs like ATS to evaluate the real-life performance of their materials and equipment.
Fatigue is a type of progressive failure that can cause cracks to propagate in a material. Common Factors Related to Fatigue Cracking:. When searching for a reputable testing service provider, look no further than Applied Technical Services. For decades, ATS has been assisting clients across numerous industries both nationally and internationally. Structural weak spots were found in the inverted nodes and the vertical struts located along the outer rim of the specimens, matching the maximum principal strain concentrations and fracture sites in the DIC and micro-CT data.
Cracks were often found to originate from internal void spaces or from sites susceptible to mode-I cracking. Many specimens maintained their structural integrity and exhibited no signs of rapid strain accumulation despite the presence of substantial crack growth. This observation underlines the importance of such microscale studies to identify accumulated damage that otherwise goes unnoticed. For testing in a marine environment for offshore application, a loading frequency of 0.
For some applications, for example, lateral buckling of offshore pipelines, the loading frequency is typically very slow. Frequency scanning FS testing is often used to determine the effect of loading frequency on FCGR in corrosive environments. The crack growth rate at any particular loading frequency is determined by calculating the slope in a plot between crack length and number of cycles. To avoid any possible transient crack growth rate data being included in the analysis, the crack growth data corresponding to the initial crack extension after each change of loading frequency is often excluded from the analysis.
In the meantime, FCGR tests are carried out in the same environment at a fixed loading frequency, typically between 0. FCGR testing in corrosive environments are required to be carried out in specialised testing facilities for environmental control such as partial pressure, pH value of solution, temperature, aqueous solution, oxygen content in solution, test gas composition, etc.
Pre-soaking is required to ensure a specimen is fully charged before testing. However, since a specimen is continuously exposed to the environment during testing, and for specimens with a crack, it is the hydrogen content in the crack tip region that will influence the FCGR behaviour, the actual pre-charging period could be less than four days. Once the FCG tests and post-test examination have been completed, statistical analysis of the data are required to determine the material constants in Eq.
The Secant method is more often used because of its simplicity. It involves calculating the slope of the straight line connecting two adjacent data points on the crack size, a, versus N curve. For the FCGR data obtained under different conditions, for example, notch position, welding procedure, microstructure, material strength and component dimensions, statistical analyses should first be carried out to determine whether the data under different conditions, belong to the same population, ie having the same FCGR curve, or whether the difference between the two sets of results is significant.
This can be carried out using the guidance on statistical analysis of fatigue data 7. If there is no significant difference in FCGR for a given significance level, the data can be combined to form one population in the following regression analysis. The data below and above the transition point are in the stages A and B, respectively.
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