Microstructural response of nanocrystalline Al to cyclic loading

The data is derived from an investigation into the microstructural changes of nanostructure Al (produced by cryo-rolling) in response to cyclic loading using electron microscopy and EBSD. The aim is to develop a better understanding of the deformation mechanisms in ultrafine grained/nanostructure metals under cyclic loading conditions.

Cyclic deformation behaviour of ultrfine-grained aluminium

Ultrafine-grained aluminium was produced by cryo-rolling and their deformation response under cyclic loading was investigated. Shear banding and grain coarsening were recognized as the main damage mechanism reducing their performance under cyclic loading. However presence of precipitates in ultrafine-grained A1 can actively hinder the operation of cyclic softening mechanisms and increase microstructural stability under cyclic loading.

Finite element simulations of the cyclic elastoplastic behaviour of copper thin films

A large-scale computational and statistical strategy is presented to investigate the development of plastic strain heterogeneities and plasticity induced roughness at the free surface in multicrystalline films subjected to cyclic loading conditions, based on continuum crystal plasticity theory. The distribution of plastic strain in the grains and its evolution during cyclic straining are computed using the finite element method in films with different ratios of in-plane grain size and thickness, and as a function of grain orientation (grains with a {1 1 1} or a {0 0 1} plane parallel to the free surface and random orientations). Computations are made for 10 different realizations of aggregates containing 50 grains and one large aggregate with 225 grains. It is shown that overall cyclic hardening is accompanied by a significant increase in strain dispersion. The case of free-standing films is also addressed for comparison. The overall surface roughness is shown to saturate within 10 to 15 cycles. Plasticity induced roughness is due to the higher deformation of {0 0 1} and random grains and due to the sinking or rising at some grain boundaries.

Influences of wind energy integration into the distribution network

Wind energy is one of the most promising renewable energy sources due to its availability and climate-friendly attributes. Large-scale integration of wind energy sources creates potential technical challenges due to the intermittent nature that needs to be investigated and mitigated as part of developing a sustainable power system for the future. Therefore, this study developed simulation models to investigate the potential challenges, in particular voltage fluctuations, zone substation, and distribution transformer loading, power flow characteristics, and harmonic emissions with the integration of wind energy into both the high voltage (HV) and low voltage (LV) distribution network (DN). From model analysis, it has been clearly indicated that influences of these problems increase with the increased integration of wind energy into both the high voltage and low voltage distribution network, however, the level of adverse impacts is higher in the LV DN compared to the HV DN.

Phase transformation evolution in NiTi shape memory alloy under cyclic nanoindentation loadings at dissimilar rates

Hysteresis energy decreased significantly as nanocrystalline NiTi shape memory alloy was under triangular cyclic nanoindentation loadings at high rate. Jagged curves evidenced discrete stress relaxations. With a large recovery state of maximum deformation in each cycle, this behavior concluded in several nucleation sites of phase transformation in stressed bulk. Additionally, the higher initial propagation velocity of interface and thermal activation volume, and higher levels of phase transition stress in subsequent cycles explained the monotonic decreasing trend of dissipated energy. In contrast, the dissipated energy showed an opposite increasing trend during triangular cyclic loadings at a low rate and 60âsec holding time after each unloading stage. Due to the isothermal loading rate and the holding time, a major part of the released latent heat was transferred during the cyclic loading resulting in an unchanged phase transition stress. This fact with the reorientation phenomenon explained the monotonic increasing trend of hysteresis energy.

Influence of backpressure during ECAP on the monotonic and cyclic deformation behavior of AA5754 and Cu99.5

Ultrafine-grained (UFG) metals produced by equal channel angular pressing (ECAP) exhibit outstanding mechanical properties. They show high strength under monotonic loading as well as strongly enhanced fatigue lives in the Wöhler S-N-plot compared to their coarse grained (CG) counterparts. It could be shown that the fatigue lives can be significantly enhanced further by applying backpressure during ECAP. Besides the positive effect of backpressure on the processability of hard to deform materials via ECAP, the hydrostatic stress induced by backpressure also influences the mechanical properties under monotonic and cyclic loading. Therefore the influence of backpressure on ECAPed Cu99.5 and on the ECAPed aluminum alloy AA5754 was investigated. It is shown that backpressure has no effect on the hardness and grain size in Cu99.5 but changes the grain boundary misorientation to higher fractions of low angle grain boundaries. Also the temperature dependency of the yield strength as well as the hardening behavior under monotonic compression is affected. The cyclic deformation behavior of Cu99.5 is not strongly influenced by backpressure, but the mean stress level changes drastically. The fatigue life increases with the application of backpressure at low plastic amplitudes due to a change in the crack initiation and propagation. Aim of this work is the investigation of the influence of backpressure during equal channel angular pressing (ECAP) on the mechanical properties under monotonic and cyclic loading. Therefore we performed hardness measurements, compression, and fatigue tests on ECAPed Cu99.5 and AA5754. The results are discussed in terms of microstructure and relevant deformation and damage mechanisms.

Cyclic carbonate–sodium smectite intercalates

Five-membered cyclic organic carbonates (COC) are of interest for their ability to modify the surface properties of smectites and enhance the hydraulic resistance of bentonites to saline leachates. The mechanism of interaction of glycerol carbonate (GC) and several other hydroxyl containing cyclic organic carbonates (generally having progressively greater molecular masses) with sodium montmorillonite (Na+-Mt) was studied using powder X-ray diffraction and infrared spectroscopy. The 001 reflection for GC/Na+-Mt intercalates varied with the amount COC added, and the measured d001 value increased from 1.29 nm to as large as 2.22 nm at equal-mass coverage of the COC to Na+-Mt. In general, when intercalated, the cyclic carbonyl (Cdouble bond; length as m-dashO) stretch and the fundamental hydroxyl (O–H) stretch bands of COC derivatives were red-shifted with respect to these bands for neat COC, indicating strong ion-dipole interaction of the carbonyl group with interlayer Na+, and H-bonding of the OH group with both interlayer water and Mt surfaces. A stable and highly ordered intercalate was produced at a 1:1 mass loading with Mt in which about 6 GC molecules per unit cell (~ 7 molecules per Na+ ion) replaced most of the interlayer water.

Numerical models of plastic zones and associated deformations for elliptical inclusions in remote elastic loading-unloading with different R-ratios

Plastic zones and associated deformations ahead of a fatigue crack are well established nowadays. In-depth plane strain elasto-plastic finite element analysis is conducted in this investigation to understand the nature of cyclic plastic deformation and damage around soft and hard elliptical inclusions. Similar to fatigue crack tip, cyclic/reverse plastic zone and monotonic plastic zone are visible for soft elliptical inclusion. In the cyclic plastic zone, low cycle fatigue is the dominant cyclic deformation mode during symmetric load cycling, while ratcheting is dominant during asymmetric load cycling. The size of cyclic plastic zone depends upon the amplitude of remote stress while, the size of monotonic plastic zone depends upon the maximum remote stress. The size of monotonic plastic zone is equal to cyclic plastic zone during symmetric load cycling. The shape and size of plastic zones also depend upon the orientation of the soft inclusion. Cyclic plastic damage progression in the cyclic plastic zone for soft (MnS) inclusion is significant, while no cyclic plastic zone is visible for hard inclusion (Al2O3).

Prediction of non-proportional cyclic hardening and multiaxial fatigue life for FCC and BCC metals under constant amplitude of strain cycling

The fatigue lives are reduced accompanying an additional cyclic hardening under strain controlled non-proportional cyclic loading in which principal directions of stress and strain are altered within a cycle. This study predicts non-proportional cyclic hardening and multiaxial fatigue life for several BCC and FCC metals under constant amplitude strain cycling. A novel procedure to determine non-proportional cyclic hardening form uniaxial tensile properties has discussed in this study. Standard plastic strain energy density based fatigue criteria with considering the non-proportional cyclic hardening effect successfully predicts multiaxial fatigue lives. The predictions of non-proportional cyclic hardening and multiaxial fatigue life through models are validated by experimental results of various BCC and FCC metals which are collected from literatures.