Fatigue & Fracture of Engineering Materials & Structures最新文献

This paper evaluates the capability of the theory of critical distances (TCD) coupled with the Fatemi–Socie (FS), Smith–Watson–Topper (SWT), and normal stress range (S-N) criteria for the lifetime estimation of combined fretting fatigue, that is, the combination of bending and axial loading modes, for 316L stainless steel along with the effect of increasing the grain size of the material. After evaluating the stress field, the point, line, area, and volume methods have been implemented to estimate the lifetimes of fretting fatigue experiments based on the dependency of the critical distance on the number of cycles to failure. Whereas the area and volume methods were overestimating the lifetimes, the point and line methods were more accurate. FS and SWT criteria were proper in lifetime estimation, but the normal stress range (S-N) criterion was not a safe criterion. At the same time, increasing the grain size of the material leads the TCD to be more conservative.

The desire to use additively manufactured (AM) parts to ensure the availability of military aircraft, and to build limited-life unmanned aerial vehicles (drones), coupled with the United States Air Force (USAF) approach to the airworthiness certification of AM parts has focused attention on durability analysis/assessment, and hence on the growth of small cracks in AM parts. Previous studies have shown that laser powder fusion built (LPBF) Scalmalloy® has: i) A yield stress and an ultimate strength that are greater than that of AA2024-T3 and comparable to that of AA7075-T6; ii) A resistance to crack growth that is better than that of AA7075-T6 and comparable to that of AA2024-T3. However, since the ability to predict the durability of a part is essential for its airworthiness certification, the present paper illustrates how to perform a linear elastic fracture mechanics (LEFM)-based durability assessment of Boeing Space, Intelligence and Weapon System (BSIWS) LPBF Scalmalloy®. The durability study includes specimens with both machined surfaces and surfaces left in the as-built condition. As a result, it would appear that BISWS AM LPBF Scalmalloy® is an ideal candidate for building limited-life AM replacement parts for fixed and rotary wing aircraft and drones.

Nickel aluminum bronze (NAB) is a complex alloy used extensively in the marine environment. Fatigue strength of NAB is reduced by welding and prior seawater corrosion. This study investigated the combined effect of corrosion and plasma welding on the fatigue behavior of NAB. Natural seawater corroded samples were used in tension-tension cyclic loading tests to observe fatigue crack initiation, propagation, and failure. Fatigue cracks initiated from corrosion pits at the weld toe. Stress corrosion and fatigue cracks propagated along the path of β′ and κ_III phases. A short crack growth model (SCGM) predicted fatigue strength using experimentally obtained material properties and corrosion pit dimensions. Model predictions were used to develop S-N curves and were within 30% of experimental results. The SCGM produced accurate and reliable fatigue life results that could be applied by industry to aid in revalidation decision making and inspection scheduling.

A reasonable crack driving force is the key to preventing compression cracks and eliminating unrealistic crack propagation in phase field fracture analysis. Thus, examining the roles of volumetric strain energy (VSE) and deviatoric strain energy (DSE) in influencing crack propagation is necessary. This paper presents a comprehensive analysis of the following four different approaches to energy decomposition-driven crack propagation: the positive volumetric strain energy method (VSEM), deviatoric strain energy method (DSEM), volumetric-deviatoric strain energy method (VDSEM), and no decomposition method (NM). All of the strain energy is involved in the development of the crack propagation. The following four examples are investigated: two benchmark single-side notched examples, a complex crack containing a hole example, and a crack coalescence in an asymmetric double notch example. The VSEM's numerical findings align with literature and experimental observations, confirming that positive VSE rather than DSE promotes crack propagation.

This study investigates the varying thermal response of additively manufactured specimens made of AlSi10Mg and subjected to cyclic loading. It is well known that the thermal response is driven primarily by the self-heating effect. The paper explores the possibility of employing thermographic methods to establish an S–N curve for fatigue life prediction with the use of fewer specimens than are traditionally required for an S–N curve established from constant-amplitude fatigue tests. Specific self-heating step tests are conducted by gradually increasing the loading amplitude while monitoring the temperature of the specimen. A new approach is introduced to assess the lower limitation of the existing Fargione method, which addresses the absence of the fatigue limit threshold in previously published works. The validity of this approach is compared with our own experimental data. This new dataset concerns additively manufactured (AM) specimens made from AlSi10Mg powder, which were all printed on a single platform. To observe the sensitivity of the updated approach, four groups with different heat treatments were evaluated.