scholarly journals Requirements and Variability Affecting the Durability of Bonded Joints

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1468 ◽  
Author(s):  
Rhys Jones ◽  
Daren Peng ◽  
John G. Michopoulos ◽  
Anthony J. Kinloch
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Upper Bound ◽  
The United States ◽  
Fatigue Threshold ◽  
Growth Equation ◽  
Bonded Joints ◽  
Cohesive Failure ◽  
Structural Adhesives

This paper firstly reveals that when assessing if a bonded joint meets the certification requirements inherent in MIL-STD-1530D and the US Joint Services Standard JSSG2006 it is necessary to ensure that: (a) There is no yielding at all in the adhesive layer at 115% of design limit load (DLL), and (b) that the joint must be able to withstand design ultimate load (DUL). Secondly, it is revealed that fatigue crack growth in both nano-reinforced epoxies, and structural adhesives can be captured using the Hartman–Schijve crack growth equation, and that the scatter in crack growth in adhesives can be modelled by allowing for variability in the fatigue threshold. Thirdly, a methodology was established for estimating a valid upper-bound curve, for cohesive failure in the adhesive, which encompasses all the experimental data and provides a conservative fatigue crack growth curve. Finally, it is shown that this upper-bound curve can be used to (a) compare and characterise structural adhesives, (b) determine/assess a “no growth” design (if required), (c) assess if a disbond in an in-service aircraft will grow and (d) to design and life in-service adhesively-bonded joints in accordance with the slow-growth approach contained in the United States Air Force (USAF) certification standard MIL-STD-1530D.

scholarly journals Modelling the Variability and the Anisotropic Behaviour of Crack Growth in SLM Ti-6Al-4V

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1400
Author(s):  
Rhys Jones ◽  
Calvin Rans ◽  
Athanasios P. Iliopoulos ◽  
John G. Michopoulos ◽  
Nam Phan ◽  
...  
Keyword(s):  
Crack Growth ◽  
The United States ◽  
Fatigue Threshold ◽  
Growth Equation ◽  
Single Edge ◽  
Test Program ◽  
Large Variability ◽  
Single Edge Notch ◽  
Anisotropic Behaviour ◽  
Edge Notch

The United States Air Force (USAF) Guidelines for the Durability and Damage Tolerance (DADT) certification of Additive Manufactured (AM) parts states that the most difficult challenge for the certification of an AM part is to establish an accurate prediction of its DADT. How to address this challenge is the focus of the present paper. To this end this paper examines the variability in crack growth in tests on additively manufactured (AM) Ti-6Al-4V specimens built using selective layer melting (SLM). One series of tests analysed involves thirty single edge notch tension specimens with five build orientations and two different post heat treatments. The other test program analysed involved ASTM standard single edge notch specimens with three different build directions. The results of this study highlight the ability of the Hartman–Schijve crack growth equation to capture the variability and the anisotropic behaviour of crack growth in SLM Ti-6Al-4V. It is thus shown that, despite the large variability in crack growth, the intrinsic crack growth equation remains unchanged and that the variability and the anisotropic nature of crack growth in this test program is captured by allowing for changes in both the fatigue threshold and the cyclic fracture toughness.

Near-Threshold Fatigue Crack Growth Behavior of ECAPed Ultrafine-Grained Copper

2021 ◽  
Vol 1016 ◽  
pp. 1193-1198
Author(s):  
Shou Dao Qu ◽  
Ze Sheng You
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Threshold ◽  
Coarse Grained ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Resistance ◽  
Ultrafine Grained ◽  
Stress Ratios ◽  
Near Threshold

Fatigue crack growth resistance of ultrafine grained Cu processed by equal channel angular pressing (ECAP) was investigated. Particular emphasis was devoted to the effects of microstructure evolution on fatigue crack growth in the near-threshold regime. The ultrafine grained Cu exhibits a lower fatigue threshold than coarse-grained Cu at stress ratios of 0.1 and 0.7. Fatigue induced coarsening of the UFG structure near the fatigue crack and intergranular fatigue crack growth are observed.

scholarly journals Optimizing Measurement of Fatigue Crack Growth Relationships for Cr-Mo Pressure Vessel Steels in Hydrogen Gas

2015 ◽  
Author(s):  
Brian Somerday ◽  
Paolo Bortot ◽  
John Felbaum
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Upper Bound ◽  
Growth Rates ◽  
Hybrid Approach ◽  
Hydrogen Gas ◽  
Design Life ◽  
Pressure Vessel Steels ◽  
Crack Growth Rates

The objective of this study was to explore an approach for measuring fatigue crack growth rates (da/dN) for Cr-Mo pressure vessel steels in high-pressure hydrogen gas over a broad cyclic stress intensity factor (ΔK) range while limiting test duration, which could serve as an alternative to the method prescribed in ASME BPVC VIII-3, Article KD-10. Fatigue crack growth rates were measured for SA-372 Grade J and 34CrMo4 steels in hydrogen gas as a function of ΔK, load-cycle frequency (f), and gas pressure. The da/dN vs. ΔK relationships measured for the Cr-Mo steels in hydrogen gas at 10 Hz indicate that capturing data at lower ΔK is valuable when these relationships serve as inputs into design-life analyses of hydrogen pressure vessels, since in this ΔK range crack growth rates in hydrogen gas approach rates in air. The da/dN vs. f data measured for the Cr-Mo steels in hydrogen gas at selected constant-ΔK levels demonstrate that crack growth rates at 10 Hz do not represent upper-bound behavior, since da/dN generally increases as f decreases. Consequently, although fatigue crack growth testing at 10 Hz can efficiently measure da/dN over a wide ΔK range, these da/dN vs. ΔK relationships at 10 Hz cannot be considered reliable inputs into design-life analyses. A possible hybrid approach to efficiently establishing the fatigue crack growth rate relationship in hydrogen gas without compromising data quality is to measure the da/dN vs. ΔK relationship at 10 Hz and then apply a correction based on the da/dN vs. f data. The reliability of such a hybrid approach depends on adequacy of the da/dN vs. f data, i.e., the data are measured at appropriate constant-ΔK levels and the data include upper-bound crack growth rates.

Comparison of Fatigue Crack Growth Curves of Japan, the United States, and European Union Code and Standards

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Kiminobu Hojo ◽  
Yukio Takahashi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Nuclear Power ◽  
Growth Curves ◽  
The United States ◽  
Austenitic Steels ◽  
Engineering Society ◽  
Asme Code ◽  
American Society

There are several codes, standards, handbooks, and guidelines for the nuclear power plant maintenance in Japan, the US, and EU. They include Stress Corrosion Cracking (SCC) and fatigue crack growth curves for crack growth calculation. In this paper, the authors selected five kinds of codes, standards and guidelines, and compared their fatigue crack growth curves for choice of the suitable curves. The feature of each curve was quantitatively evaluated. Japan Society of Mechanical Engineers (JSME) maintenance rule and American Society of Mechanical Engineers (ASME) code provide the fatigue crack growth formulae for both ferritic and austenitic steels and consider the environmental effects in some cases. The Fitness-for-Service Network (FITNET) curves are categorized in many kinds of metal, whereas the Forschungskuratorium Maschinenbau (Germany) = Board of Trustees of Mechanical Engineering (FKM) guideline and Welding Engineering Society (WES) procedure provide the common properties generally applicable to steels.

scholarly journals Fatigue Measurement of Pipeline Steels for the Application of Transporting Gaseous Hydrogen1

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Andrew J. Slifka ◽  
Elizabeth S. Drexler ◽  
Robert L. Amaro ◽  
Louis E. Hayden ◽  
Douglas G. Stalheim ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Yield Strength ◽  
Crack Growth ◽  
Upper Bound ◽  
American Petroleum Institute ◽  
Hydrogen Gas ◽  
Growth Data ◽  
Pipeline Steels ◽  
Code Modification

A comprehensive testing program to determine the fatigue crack growth rate (FCGR) of pipeline steels in pressurized hydrogen gas was completed. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and 0.01 Hz. Of particular interest was whether the X70 materials would exhibit higher FCGRs than the X52 materials. The American Petroleum Institute steel designations are based on specified minimum yield strength (SMYS), and monotonic tensile tests have historically shown that loss of ductility correlates with an increase in yield strength when tested in a hydrogen environment. The X70 materials performed within the experimental spread of the X52 materials in FCGR, except for the vintage X52 material at low (5.5 MPa) pressure in hydrogen gas. This program was developed in order to provide a modification to the ASME B31.12 code that is based upon fatigue, the primary failure mechanism in pipelines. The code modification is a three-part Paris law fit of the upper bound of measurements of FCGR of pipeline steels in pressurized hydrogen gas. Fatigue crack growth data up to 21 MPa (3000 psi) are used for the upper bound. This paper describes, in detail, the testing that formed the basis for the code modification.

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