Advanced Materials Research Vols. 891-892

Abstract: It is known that particle size has an influence in determining the erosion rate, and hence equipment life, on a target material in single phase flows (i.e. flow of solid particles in liquid only or gas only flows). In reality single phase flow is rarely the case for field applications in the oil and gas industry. Field cases are typically multiphase in nature, with volumetric combinations of gas, liquid and sand. Erosion predictions of multiphase flows extrapolated from single phase flow results may be overly conservative. Current understanding of particle size distribution on material erosion in multiphase flows is limited. This work examines the effect of particle size distribution on material erosion of a cylindrical aluminium rod positioned in a 2" vertical pipe under slug and distributed bubble regimes using various water and air volume ratios. This is achieved through physical erosion experiments and computational fluid dynamics (CFD) simulations tailored to account for particle dynamics in multiphase flows.

Abstract: The cyclic deformation behavior and fatigue characteristics of a new austenitic manganese steel with composition FeMn18Cr7C0.8N0.2 (wt%) have been explored and analyzed based on the partition of hysteresis loops linked with microstructure by low cycle testing in the total strain amplitudes 0.3% - 1.0%. The new N+C austenitic manganese steel exhibited immediate cyclic softening for small strain amplitude and initial hardening at the onset of fatigue life followed by softening for medium and high strain amplitudes. For low and high strain amplitudes the evolution of internal stress and effective stress partitioned from the hysteresis loop with the prolonged cycles both corresponded to the change in the total stress amplitudes. With the exception of 316LN0.2 austenitic stainless steel, the effective stress and internal stress made a contribution to the cyclic deformation behavior with similar effect. The markedly improved contribution of effective stress in the new N+C austenitic manganese steel was attributed to the enhanced short range order caused by N+C alloying whereas the decreasing of effective stress with the number of cycles was because of this broken short range interaction. TEM observations showed that the significantly increased planar dislocation structures due to the presence of N+C were responsible for the strong tendency to cyclic softening, in association with the decrease of effective stress and internal stress simultaneously. Moreover the fatigue short crack could be observed on the fractured sample surface at high strain amplitude.

Abstract: Efficiency increase of combustion engines in automotive development is directly related to improved material performance at high temperatures. In particular, the interaction of complex thermal and mechanical forces under service loading is one of the major factors affecting the lifetime. In this paper the aluminium cylinder head alloy AlSi6Cu4 is characterized concerning the high temperature low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) behaviour. Experiments were performed in air at temperatures between 200 and 400°C. The influence of the initial heat treatment and microstructure, testing temperatures, strain amplitudes and strain rates is reported. Two heat treatment modifications (i.e. overaged condition, T7, and a modified combined heat treatment, hot iso-static pressing (HIP), prior to peak hardening according to T6) are compared to the T6 standard used in service. The strain amplitudes ranged between 0.2 to 0.7%. For the standard T6 heat treatment LCF results at 400°C indicate increased ductility and longer lifetimes compared to 200°C. For the overaged microstructure and the modified treatment HIP + T6 under TMF exposure clear lifetime enhancements are observed which are significantly highest for the HIP + T6 version. Thus, the elimination of almost any microporosity reduces local stress concentrations and early crack initiation promoting failure. Special attention is focussed on microstructural changes during high temperature exposure.

Abstract: The ability to optimise structures requires a thorough understanding of the loadsthat they are subjected to. Many composite materials in use today are subjectedto complex loading patterns that exhibit multi-axial stress and straincharacteristics. It is not sufficient to model material data for thesestructures based purely on uniaxial information. Unlike the well understoodfailure criteria of materials when subjected to uniaxial loads; biaxial failureenvelope has not been defined with sufficient experimental data particularly inthe tensile load region. There has not been any standard specimen geometrydefined for biaxial testing. Also the effective area when subjected to loadingis not as easily known as is the case in uniaxial loading. Thus biaxial testspose a greater level of difficulty when establishing failure stresses for thematerial. The authors look at establishing a specimen geometry that is suitablefor use preliminarily in isotropic materials. These specimen geometries must beable to ensure failure at the anticipated gauge region. Investigation into thefirst quadrant of the biaxial failure envelope under tension-tension is lookedat with insight into matrix failure as the dominant mode of failure. Numerical resultsand preliminary experimental results for FM355 epoxy specimens are presentedand compared with existing failure models such as Von Mises criterion and thefailure criterion used in Strain Invariant Failure Theory.

Abstract: The aim of this study is to develop a statistical estimation method of S-N curve for iron and structural steels by using their static mechanical properties. In this study, firstly, the S-N data for pure iron and structural steels were extracted from "Database on fatigue strength of Metallic Materials" published by the Society of Materials Science, Japan (JSMS) and S-N curve regression model was applied based on the JSMS standard, "Standard Evaluation Method of Fatigue Reliability for Metallic Materials -Standard Regression Method of S-N Curve-". Secondly, correlations between regression parameters and static mechanical properties were investigated. As a result, the relationship between the regression parameters and static mechanical properties (e.g. fatigue limit E and static tensile strength σ_B) showed strong correlations, respectively. Using these correlations, it is revealed that S-N curve for iron and structural steels can be predicted easily from the static mechanical properties.

Abstract: This study describes the mechanisms of emergence and propagation of fatigue cracks caused by mechanical tension stress fluctuations in dissimilar steels butt and overlap welded joints under axial tension fatigue loads. A structural (ASTM A537, class I) and a stainless (ASTM A240, 304L) were soldiers through GMAW, Argon as protecting gas and a stainless (ASTM A240, 308L) as a supplier material, not being submitted to pre and post welding thermal treatment. Microstructures (Scanning Electron Microscopy, SEM) were contrasted in different zones of each joint, focus on Heat Affected Zone (HAZ) and fusion lines. Samples were inspected by not destructive test (penetrating liquids and ultrasound), to discard surface and internal defects. The following mechanical tests were compared between both welding joint (WJ): Vickers hardness profile, tension, bending, impact, axial fatigue, and speed of propagation of fatigue cracks. Vickers show high values of micro hardness in the HAZ, near the fusion line between weld and stainless. Tension and axial fatigue tests indicated similar behavior between WJ and structural (butt joint); and similar behavior between WJ and stainless (overlap joint). Pre-cracked test evidence a faster growth of crack in the fusion line between structural steel and stainless. Dissimilar unions (butt and overlap) have mechanical and microstructure properties, which can be considered adequate to withstand the mechanical requirements in service conditions, despite relatively high values of hardness in the HAZ, particularly in the fusion line between the welding cord and the stainless 304L, as well as inclusions between the structural and the stainless one.

Abstract: Multiple-site Damage (MSD) is a dangerous scenario for aircraft structures due to the interaction of adjacent cracks in one structural element. Despite their excellent fatigue crack growth resistance, Fibre Metal Laminates (FMLs) may also encounter this damage scenario. However, only few studies on fatigue crack growth in presence of MSD in FMLs has been reported. An overview of the relevant methods for predicting the crack propagation properties of MSD in FMLs is given and discussed in this paper. The fatigue crack growth of MSD in FMLs was experimentally studied and is reported in this paper. A new analytical methodology, based on the superposition principle and displacement compatibility method, is proposed.

Abstract: Fatigue crack propagation behaviors coupled with the microstructure evolution of a hardworking Ni-based superalloy after long-time aging at 1023K were studied, to provide fundamental data for the fatigue life prediction of the superalloy. The results show that the microstructures remarkably change and the fatigue crack propagation resistance decreases with the aging time prolongs. It is found that the precipitation and the growth of topologically close packed (TCP) phases as well as the coarsening of γ' phase and carbides on grain boundaries can significantly affect the fatigue crack growth rate. On one hand, coarsened γ' phase and carbides at grain boundaries block dislocation movements near the crack tip, thus the fatigue crack propagation is hindered in near-threshold region and Paris region. On the other hand, the stress concentration accumulates continually with carbides precipitation increases, so that the grain boundaries become the main fatigue crack propagation rout. As well as, the effect of the TCP phases on the fatigue crack propagation behavior ascribes to the size and the distribution of TCP phases. Very small quantity of TCP phases contribute to pinning dislocation and enlarging fatigue crack propagation absorption energy, but high quantity of TCP phases with short rod shape changed to the needle, which gradually precipitate uniformly within the grain after 1000h besides on grain boundaries in the earlier aging, leads to much higher stress concentration degree. Those discussed above are the most important reasons why the fatigue crack growth rate increases after long-time aging.

Abstract: Strain-gradient and non-Euclidean continuum theories are used for the construction of non-classical solutions of continuum models. Both models result in identical structures in terms of their kinematic and force characteristics. The obtained solutions exhibit a critical behavior with respect to the external loading parameter. The proposed analysis allows us to use different theoretical approaches for descriptions of rock critical behavior under different loading conditions.

Abstract: The paper highlights key questions in ensuring safe operation of aging civil\transport aircraft in Russia. Presented is the analysis of current requirements to fatigue, fail-safe and damage tolerance for transport aircraft structures stated in FARs, Advisory Circulars (UAS) and Russian Airworthiness Regulations\ AR IAC Aviation Regulations. The paper gives the design goals and actual service life values\ service years of aging aircraft fleet and data on full-scaled fatigue tests, together with methods and approaches to ensure safe operation of aircraft structures in case of multiple site damages, corrosion and materials degradation for Russian aging fleet.