Plate Normal Direction Research Articles

Deformation and fracture behavior of Mg alloy, WE43, after various aging heat treatments

Wrought Mg alloy, WE43, is normally artificially aged after hot working (T5 temper). A solutionizing heat treatment is revealed to weaken the initial basal texture of the hot-rolled plate, which resulted in a reduction of the yield strength anisotropy (by notably lowering the in-plane strength). Solutionizing followed by peak aging (T6 temper) only leads to a marginal increase in hardness. The precipitate size and volume fraction are slightly greater for T6 as compared to T5. Different strategies to increase the number density of the precipitates were explored. T8 treatments (where the solutionized material is cold-deformed prior to aging) were carried out, and although the aging kinetics improved, the peak hardness did not. Similarly, two-step aging (first at 140°C for 4h, followed by 210°C) treatment provided no measurable increase in hardness. The T6 samples showed large grain boundary precipitates and a larger precipitate free zone, as compared to T5, which resulted in extensive intergranular ductile fracture, and reduced ductility. Finally, the lower ductility along the plate normal direction is related to stringers of Y-rich cuboidal dispersoids. The results reveal the incumbent T5 temper to be an optimum in terms of strength, ductility, and energy consumption.

On the trajectory of leading-edge vortices under the influence of Coriolis acceleration

Leading-edge vortices (LEVs) can form and remain attached to a rotating wing indefinitely, but the mechanisms of stable attachment are not well understood. Taking for granted that such stable structures do form, a practical question arises: what is the trajectory of the LEV core? Noting that span-wise flow exists within the LEV core, it is apparent that a mean streamline aligned with the axis of the stable LEV must exist. The present work uses the Navier–Stokes equations along such a steady, axial streamline in order to consider the accelerations that act in the streamline-normal direction to affect its local curvature. With some simplifying assumptions, a coupled system of ordinary differential equations is derived that describes the trajectory of an axial streamline through the vortex core. The model is compared to previous work, and is found to predict the trajectory of the LEV core well at span-wise locations inboard of the midspan. This result suggests that Coriolis acceleration is responsible for limiting the span-wise extent of a stable LEV by tilting it into the wake within several chord lengths from the centre of rotation. The downwash due to the tip vortex also appears to play a role, as the only significant differences between model-predicted LEV trajectories and previous results are in the plate-normal direction.

Dependence of compressive deformation on pre-strain and loading direction in an extruded magnesium alloy: Texture, twinning and de-twinning

This study was aimed at identifying compressive deformation behavior of an extruded AM30 magnesium alloy after different amounts of pre-strain along the extrusion direction (ED), with focus on the effect of re-loading direction, texture evolution, and deformation mechanisms. Compressive loading in both ED and transverse direction (TD) resulted in a similar sigmoidal true stress–true strain behavior due to the presence of two sets of basal textures with c-axes aligned nearly parallel to the plate normal direction which facilitated the occurrence of {101¯2} extension twinning. In the two-step ED–ED compression, the compressive yield strength (YS) linearly increased, while the ultimate compressive strength (UCS) and hardening capacity linearly decreased with increasing pre-strain. The disappearance of twin boundaries or the coalescence of twins via twin growth was observed, but the twin boundaries were more visible and the intensity of cumulative textures with c-axes rotating towards the anti-compression direction was lower, in comparison with the one-step continuous compression at an equivalent strain level. In the two-step ED–TD compression, both YS and UCS increased, and hardening capacity decreased with increasing pre-strain. After a 4.0% pre-strain along the ED plus 4.0% re-compression along the TD, two seemingly opposite phenomena, i.e., the formation of new twins and de-twinning were observed to be co-existent due to the presence of multiple sets of textures after the first-step pre-straining. Both the reversal of textures and microstructural examinations corroborated the occurrence of de-twinning or twin narrowing/shortening as a result of the change of deformation path in the second-step compression.

Modeling lattice strain evolution during uniaxial deformation of textured Zircaloy-2

An elastoplastic self-consistent model was used to interpret the experimental lattice strain evolution previously reported for testing in three directions of a thick polycrystalline Zircaloy-2 slab. The model was used to infer the underlying deformation mechanisms. The influences of prism 〈 a〉 slip, basal 〈 a〉 slip, pyramidal 〈 c + a〉 slip and tensile twinning were considered. The critical resolved shear stresses and hardening parameters for each mode were obtained by simultaneously fitting the macroscopic flow curves, Lankford coefficients and internal elastic strain development for all diffraction peaks, for the combination of three measurement directions and three loading directions, for compression and tension. The effects of dislocation interactions during deformation and hardening between deformation modes were considered. Tensile twinning inferred from the intensity changes of the diffraction peaks and its activity was qualitatively reproduced by the simulations for compression in the plate rolling and transverse directions and tension in the plate normal direction.

Anisotropy of Young's modulus and tensile properties in cold rolled α′ martensite Ti–V–Sn alloys

Young's modulus and tensile properties of cold rolled Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloy plates consisting of α′ martensite were investigated as a function of tensile axis orientation in this work. A single phase of α′ (hcp) martensite is obtained in Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloys by quenching after solution treatment. By 86% cold rolling, acicular α′ martensite microstructures change into extremely refined dislocation cell-like structure with an average size of 60 nm, accompanied with the development of cold rolling texture in which the basal plane normal is tilted from the plate normal direction (ND) toward transverse direction (TD) at angles of ±49° for Ti–8% V alloy and ±46° for (Ti–8 mass% V)–4 mass% Sn alloy. No apparent anisotropy of Young's modulus ( E) is observed for as-quenched Ti–8% V ( E = 76–83 GPa) and (Ti–8% V)-4%Sn ( E = 69–79 GPa). In contrast, Young's modulus increases with increasing angle from the rolling direction (RD) to TD for cold rolled Ti–8% V ( E = 72–94 GPa) and (Ti–8% V)–4%Sn ( E = 63–85 GPa). The observed anisotropy of Young's modulus can be reasonably explained in terms of the cold rolling α′ texture. 0.2% proof stress and tensile strength are independent of tensile orientation for cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys. In contrast, larger elongation to fracture is obtained in specimens deviated by 30°, 45° and 60° from RD than by 0°, 75° and 90°. Scanning electron microscopy (SEM) fractographs reveal that quasi-cleavage-like fracture plane appears in 0° specimen of cold rolled Ti–8% V which shows brittle fracture and other specimens of cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys are fractured accompanied with necking and dimple formation. It is suggested from these results that brittle fracture is related to the activation of limited number of slip system and Sn addition leads to the activation of multiple slip systems.

Development of internal strains in textured Zircaloy-2 during uni-axial deformation

Internal strains can greatly affect the mechanical performance of Zircaloy-2 and the study of their development provides insight into the operating deformation mechanisms. In this study, neutron diffraction was used to track the development of internal strains in three dimensions in samples cut from a rolled Zircaloy-2 slab. The samples were subjected to room temperature compression or tension in situ in the neutron diffractometer with loading along each of the three principal directions of the slab. The recorded intensity changes for the different crystallographic planes also provided information on the grain reorientations during deformation. Strong evidence was found for tensile twinning in tensile tests in the plate normal direction and in compression tests in the transverse and rolling directions. This provides an extensive data set with which to develop and test models for plastic deformation and texture development in polycrystalline Zircaloy-2.

Electron-beam welding behavior in Mg-Al-based alloys

The electron-beam welding (EBW) behaviors of pure Mg and the AZ31, AZ61, and AZ91 Mg alloys are examined in this study, in terms of fusion-zone characteristics, grain structures, texture evolution, and joint efficiency. With increasing A1 content, the Mg-based materials were found to be more easily fusion welded. The AZ91 alloy could be welded using a beam power of 2200 W and a weld speed of 16 mm/s, resulting in a weld depth of 29 mm with a fusion-zone aspect ratio of 8.2. The grains inside the fusion zone were nearly equiaxed in shape and ∼10 µm in size, due to the rapid cooling rate. Extended partial melting zones were observed in alloys with high solute contents, such as AZ61 and AZ91. The postweld tensile strength of the Mg alloys could recover back to ∼80 to 110 pct of the original strength. The texture in the fusion zone was traced by X-ray diffraction (XRD) and electron-backscattered diffraction (EBSD). The grain orientations inside the rapidly solidified electron-beam-welded fusion zones are still rather diversely distributed. The α 1-, α 2-, and α 3-axes of some grains tend to align at 90 or 30 deg with respect to welding direction, and the c-axis tends to align along the plate normal direction. The influence from surface tension on the weld top-surface appearance and weld depth was not pronounced for the current four Mg materials. Instead, differences in the solidus temperatures and thermal conductivity should be the primary factors.

Microtexture in the friction-stir weld of an aluminum alloy

In order to characterize plastic flow during friction-stir welding, the microtextures in a friction-stir weld of the precipitation-hardened aluminum alloy 6063 have been analyzed by orientation imaging microscopy (OIM). The base-material plate has a Goss orientation. The weld center region, except for the upper surface, takes a typical shear texture component with two types of orientations. The orientations have a pair of common {111} and 〈110〉 parallel to the cylindrical pin surface and transverse direction of the plate, respectively. The typical texture component is also observed around the weld center on the midsection, although it rotates about the plate normal direction. A microtexture analysis after postweld heat treatment has suggested that dynamic recrystallization during friction-stir welding generates the recrystallized grains at the weld center.

Sound radiation from two semi-infinite dissimilar plates subject to a harmonic line force excitation in mean flow. II. Asymptotics and numerical results

Asymptotic formulations are derived for describing far-field acoustic radiation from two semi-infinite dissimilar plates subject to an harmonic line force excitation at the joint in the presence of mean flow. Analysis shows that mean flow affects the acoustic pressure in three ways: (1) It enhances the wave number and amplitude of an acoustic wave propagating in the upstream direction, while it suppresses those of an acoustic wave propagating in the downstream direction; (2) it reduces the decay rate of the upstream propagating wave, while it increases that of the downstream propagating wave as they propagate in the plate normal direction; and (3) it rotates the radiation beam angles toward the downstream direction. The effects of mean flow are obvious when the excitation frequency is above the plate coincidence frequency, but decays significantly at low frequencies. The condition at the joint of two plates does not change the characteristics of the radiation pattern, but merely the amplitude of the radiated acoustic pressure. The looser the joint, for example, two plates being mechanically unconnected, the higher the amplitude of the resulting acoustic pressure.

Sound radiation from two semi-infinite dissimilar plates subject to a harmonic line force excitation in mean flow. Part II: Asymptotic formulation and numerical results

Asymptotic formulations are presented for describing radiated acoustic pressures from two semi-infinite dissimilar plates subject to a line force excitation at the joint in mean flow. Analysis shows that mean flow affects acoustic radiation in three ways: (1) it enhances the wave number and amplitude of an acoustic wave propagating in the upstream direction, while suppresses those of an acoustic wave propagating in the downstream direction; (2) it reduces the decay rate of the upstream propagating wave in the plate normal direction, while increases that of the downstream propagating wave; and (3) it rotates radiation beam angles toward the downstream direction. The effects of mean flow are obvious when the excitation frequency is above the plate coincidence frequency, but reduced significantly below the coincidence frequency. The joint condition does not change the characteristics of the radiation patterns, but merely their amplitudes. The looser the joint, the higher the amplitude of the resulting acoustic pressure. The asymptotic results agree very well with those obtained by direct numerical integrations in the far field. Numerical results for the evanescent, traveling, and radiated waves in the near field from two dissimilar plates under welded, hinged, and mechanically unconnected joints are also demonstrated. [Work supported by ONR.]

Estimation of Plate Vibration and Its Far Field Sound by Means of Near Field Sound Measurement

As one approach to noise problem of machinery, advantages of near field sound measurement are discussed for a resonating rectangular steel plate. A proposed technique after Acoustic Intensity Method was applied to measure the distributions of both intensity and particle velocity over a plane placed close to a sound source. Particle velocity in the normal direction of plate proved to be reliable for estimating the vibration of the plate surface. And far field sound pressure is calculated accurately from it. In addition, for the ease of calculating far field sound pressure form a known mode of vibration, a simple approximation by which the sound source can be replaced by the least number of point sources, is also proposed.