High-magnitude stresses induced by mineral-hydration reactions

Fluid-rock interactions play a critical role in Earth’s lithosphere and in engineered subsurface systems. In the absence of chemical mass transport, mineral-hydration reactions will be accompanied by a solid-volume increase that may induce differential stresses and associated reaction-induced deformation processes, such as dilatant fracturing to increase fluid permeability. However, the magnitudes of stresses that manifest in natural systems remain poorly constrained. Here we show that the simplest hydration reaction in nature MgO + H2O⇔ Mg(OH)2 can induce stresses of several hundred megapascals, with local stresses up to ∼1.5 GPa. We demonstrate that these stresses are dissipated not only by fracturing but also induce plastic deformationwith dislocation densities (10^15m−2) exceeding those typical of tectonically deformedrocks. If these reaction-induced stresses can be transmitted across larger length scales they may influence the bulk stress state of reacting regions. Moreover, the structural damage induced may be the first step towards catastrophic rock failure, triggering crustal seismicity.

Dynamics and stability of skyrmions in a bended nano-beam

Magnetic skyrmions are attracting much attention due to their nontrivial topology and high mobility to electric current. Nevertheless, suppression of the skyrmion Hall effect and maintaining high velocity of skyrmions with low energy cost are two major challenges concerning skyrmion-based spintronic devices. Here we show theoretically that in a nano-beam suffering appropriate bending moment, both Bloch-type and Néel-type skyrmions move with a vanishing Hall angle under a current density smaller than that required when the bending is absent. Moreover, bending alone can be used to move skyrmions, whose velocity is solved analytically from the Thiele equation. Generally speaking, inhomogeneous elastic fields affect the stability and dynamics of skyrmions, where the local stability is dominantly determined by the local bulk stress. These findings throw new light on how to drive skyrmions straightly with lower energy cost, which is vital for utilizing skyrmions as information carriers.

Effect of wearing diapers on toddler’s gait

Gait maturation in infants develops gradually through several phases. However, external factors such as childrearing practices, especially the wearing of diapers, may affect an infant’s motor development. This study investigated the influence of different bulk stresses on the gait of toddlers wearing a disposable diaper. Twenty-six healthy toddlers (age: 19.2 ± 0.9 months) participated in this study. We measured the joint kinematics (pelvis angle and hip-joint angle) and spatiotemporal parameters (step length and step width) of the toddlers’ gait under four dress conditions (wearing Type A_WET, Type A_DRY, and Type B_WET diapers and naked). Type B_WET had a higher bulk stress than Type A_WET, and Type A_DRY had lower stress than Type A _ WET. Our results indicate that the walk of toddlers when wearing a diaper differs from that when naked. This difference is due to the effect of the bulk of the diaper on the lower limb. A high bulk stress has a greater influence than that of a low bulk stress on joint dynamics and step width. Therefore, our findings suggest that wearing diapers with high bulk stress may inhibit the natural gait patterns of toddlers.

Nondestructive Photoelastic and Machine Learning Characterization of Surface Cracks and Prediction of Weibull Parameters for Photovoltaic Silicon Wafers

A nondestructive photoelastic method is presented for characterizing surface microcracks in monocrystalline silicon wafers, calculating the strength of the wafers, and predicting Weibull parameters under various loading conditions. Defects are first classified from through thickness infrared photoelastic images using a support vector machine learning algorithm. Characteristic wafer strength is shown to vary with the angle of applied uniaxial tensile load, showing greater strength when loaded perpendicular to the direction of wire motion than when loaded along the direction of wire motion. Observed variations in characteristic strength and Weibull shape modulus with applied tensile loading direction stem from the distribution of crack orientations and the bulk stress field acting on the microcracks. Using this method it is possible to improve manufacturing processes for silicon wafers by rapidly, accurately, and nondestructively characterizing large batches in an automated way.

Defect CFT techniques in the 6d $$ \mathcal{N} $$ = (2, 0) theory

Surface operators are among the most important observables of the 6d $$ \mathcal{N} $$ N = (2, 0) theory. Here we apply the tools of defect CFT to study local operator insertions into the 1/2-BPS plane. We first relate the 2-point function of the displacement operator to the expectation value of the bulk stress tensor and translate this relation into a constraint on the anomaly coefficients associated with the defect. Secondly, we study the defect operator expansion of the stress tensor multiplet and identify several new operators of the defect CFT. Technical results derived along the way include the explicit supersymmetry tranformations of the stress tensor multiplet and the classification of unitary representations of the superconformal algebra preserved by the defect.

Experimental Studies into the Analysis Required for the Durability Assessment of 7075 and 6061 Cold Spray Repairs to Military Aircraft

This paper presents an experimental study into the analysis required for the durability assessment of 7075 and 6061 cold spray repairs to military aircraft. To this end, it is first shown that provided the bulk stress in a 7075 cold spray coating can be kept beneath approximately 150 MPa, then the coating should not crack. A range of examples are presented in which the interface between the coating and the substrate only fails subsequent to crack growth in the substrate. We also show that failure of cold spray repaired/coated panels can also be due to the nucleation and growth of cracks in the substructure immediately adjacent to the coated/repaired region. As such, when performing a durability analysis for a cold spray repair, the growth of such small naturally occurring cracks, both at the interface and immediately adjacent to the ends of the coating, need to be accounted for.

Resilient Properties of Soil-Rock Mixture Materials: Preliminary Investigation of the Effect of Composition and Structure

The physical composition and stress state of soil-rock mixture (SRM) materials have a crucial influence on their mechanical properties, and play a vital role in improving the performance of subgrade. To reveal the resilient behavior and mesostructure evolution of SRM materials, triaxial tests and discrete element method (DEM) numerical analysis have been carried out. In the triaxial test section, the mechanical response of SRM materials was investigated by preparing samples under different stress states and physical states and conducting triaxial tests on samples. Simultaneously, a new irregular particle modeling method was developed and applied to the discrete element modeling process to analyze the mesostructure evolution of SRM materials under cycling loading. First, a cyclic triaxial test of SRM material is performed on the SRM material, and the effects of bulk stress, octahedral shear stress and rock content on the resilient modulus of the SRM material are analyzed. It is revealed that the resilient modulus increases with increasing bulk stress and rock content, and decreases with increasing octahedral shear stress. Based on a new resilient modulus prediction model, the relationships among the rock content, stress state and resilient modulus are established. Then, based on an improved DEM modeling method, a discrete element model of the SRM is established, and the influence of rock content on coordination number and mesostructure evolution of the SRM is analyzed. The results show that in SRM materials, the increase of crushed rock changes the mesostructure of the SRM material. With the increase of rock content, the internal contact force changes from “between soil and rock” to “between rocks”, and the skeleton formed in the rocks gradually develops overall stiffness. Under the condition of low stress, the anisotropy of the SRM material is mainly caused by the shape and grade distribution of crushed rock. The induced anisotropy caused by the change of stress state has little effect on its mechanical behavior, which may lead to the greater dispersion of multiple SRM test results.

The effect of garnet and muscovite on the recrystallized grain size of quartz from general shear experiments

<p>To investigate the role of strong and weak secondary phases on the recrystallized grain size of quartz, we performed grain size analyses on quenched samples from general shear experiments on quartz-garnet and quartz-muscovite mixtures. Six general shear experiments were conducted in the Griggs apparatus; three with mixtures of quartz-garnet (vol.% garnet 5, 15, 30) and three with mixtures of quartz-muscovite (vol.% muscovite 5, 10, 25). The starting powders for both set of experiments were synthetic mixtures of quartz-muscovite or quartz-garnet with 0.1 wt.% water added. The quartz-garnet experiments were conducted at 900°C, a pressure of 1.2 GPa, and a shear strain rate of ~10<sup>-5</sup> s<sup>-1</sup>, while the quartz-muscovite experiments were conducted at 800°C, a pressure of 1.5 GPa, and a shear strain rate of ~10<sup>-5</sup> s<sup>-1</sup>. At these deformation conditions quartz is stronger than muscovite and weaker than garnet. We observed that the bulk strength of the aggregate decreases with a greater volume percent of muscovite and increases with a greater volume percent of garnet. Garnet at these conditions does not deform plastically. The presence of secondary phases within the deforming aggregate causes stress concentrations and partitioning of strain rate between the different phases relative to the measured bulk stress and strain rate. The degree of partitioning is primarily related to the rheology and volume percent of the phases. Due to the piezometric relationship between recrystallized grain size and stress, we can use the quartz recrystallized grain size to determine the local stress of quartz in the experiments and compare it to the measured bulk stress. The results from these analyses will provide new insight into the effect of strain partitioning in general and of strong and weak secondary phases on quartz rheology.</p>