Influence of Poisson Effect of Compression Anchor Grout on Interfacial Shear Stress

The distribution and magnitude of the shear stress at the interface between the grout of a compression anchor rod and rock are strongly affected by the Poisson effect. To quantitatively analyze the influence of the Poisson effect on the interfacial shear stress of compression anchor rods, the equations for calculating the axial force and interfacial shear stress at the grout cross section in the anchorage section are derived in this paper, accounting for the Poisson effect of the grout. Based on the analytical solution, a new equation of the influence coefficient of the Poisson effect is proposed to quantitatively evaluate the influence of the Poisson effect on the interfacial shear stress. Distributions of the interfacial shear stress and the influence coefficient of the Poisson effect are analyzed with different parameter values. There is a neutral point in the anchorage section near the bearing plate, at which the magnitude of the shear stress is not affected by the Poisson effect. When the Poisson effect is considered, the interfacial shear stress from the neutral point to the bearing plate increases, and the distribution curve becomes steep. However, the interfacial shear stress far from the neutral point is low, and the distribution curve becomes smooth. Overall, the Poisson effect leads to a more nonuniform distribution of the shear stress at the interface of the compression anchor rod. A larger Poisson's ratio, smaller elastic modulus, and smaller diameter of the grout lead to a greater influence of the Poisson effect. Furthermore, a larger elastic modulus of rock leads to a greater influence of the Poisson effect. The Poisson's ratio of rock and that of grout both affect the Poisson effect greatly, but the influence of the variation in the Poisson’s ratio of rock on the Poisson effect is negligible. A larger interface friction angle leads to a greater influence of the Poisson effect.

Perceptual Properties of the Poisson Effect

When an elastic material (e.g., fabric) is horizontally stretched (or compressed), the material is compressed (or extended) vertically – so-called the Poisson effect. In the different case of the Poisson effect, when an elastic material (e.g., rubber) is vertically squashed, the material is horizontally extended. In both cases, the visual system receives image deformations involving horizontal expansion and vertical compression. How does the brain disentangle the two cases and accurately distinguish stretching from squashing events? Manipulating the relative magnitude of the deformation of a square between horizontal and vertical dimensions in the two-dimensional stimuli, we asked observers to judge the force direction in the stimuli. Specifically, the participants reported whether the square was stretched or squashed. In general, the participant’s judgment was dependent on the relative deformation magnitude. We also checked the anisotropic effect of deformation direction [i.e., horizontal vs. vertical stretching (or squashing)] and found that the participant’s judgment was strongly biased toward horizontal stretching. We also observed that the asymmetric deformation pattern, which indicated the specific context of force direction, was also a strong cue to the force direction judgment. We suggest that the brain judges the force direction in the Poisson effect on the basis of assumptions about the relationship between image deformation and force direction, in addition to the relative image deformation magnitudes between horizontal and vertical dimensions.

Two-Dimensional Piezoresistive Response and Measurement of Sensitivity Factor of Polymer-Matrix Carbon Fiber Mat

Based on the piezoresistive effect, the piezoresistive constitutive relation of a carbon fiber mat under orthogonal strain was deduced. Considering the Poisson effect, the piezoresistive responses and measurement of the sensitivity factor of a polymer-matrix carbon fiber mat under bidirectional strain were studied by a two-times uniaxial tension loading method in different directions, which was pasted in the center area of a cruciform aluminum substrate. The relations between the resistance change rate and the orthogonal strains were established, the reasonability of which was confirmed by comparison with the experimental results. The results show that the longitudinal piezoresistive sensitivity factor C11 is 21.55, and the lateral piezoresistive sensitivity factor C12 is 24.15. Using these factors, the resistance change rate of another polymer-matrix carbon mat was predicted, which was made by the same technique, and the error between the predicted and the experimental results was 1.3% in the longitudinal direction and 6.1% in the lateral direction.

Negative Piezoresistive Effect in a Stretchable Device Based on a Soft Tunneling Barrier

Piezoresistive soft composite materials are widely used in strain sensing and typically exhibit a decrease in conductivity upon elongation—the so-called positive gauge effect. We demonstrate a thin-film architecture that features the inverse behavior: a strain-induced transition from insulating to metallic conductivity, spanning nine orders of magnitude in conductivity. Our approach is based on a nanometer-scale sandwiched bilayer Au thin film with a polydimethylsiloxane elastomeric barrier layer. Upon application of strain, the thickness of the thin soft barrier decreases because of the strain governed by the Poisson effect, followed by electron-tunneling currents through the barrier, forming an interconnected bilayer metal electrode. An extremely high on–off electrical conductivity ratio (~ 109) is observed over a wide range of working strains (as high as 130%), which mimics the ideal features of a mechanical-force-controlled electric transistor. This conceptual design strategy is expected to benefit a wide range of applications in which operation under minimal standby power could be an essential feature, such as in implantable soft strain sensors and in prosthetic long-term monitoring systems for detecting sudden a swelling/volume expansion of human body organs or blood vessels, thereby helping to avoid acute and severe syndromes.

The Maximum Stress Failure Criterion and the Maximum Strain Failure Criterion: Their Unification and Rationalization

The maximum strain failure criterion is unified with the maximum stress failure criterion, after exploring the implications of two considerations responsible for this: (1) the failure strains for the direct strain components employed in the maximum strain criterion are all defined under uniaxial stress states, not uniaxial strain states, and (2) the contributions to the strain in a direction as a result of the Poisson effect do not contribute to the failure of the material in that direction. Incorporating these considerations into the maximum strain criterion, the maximum stress criterion is reproduced. For 3D stress/strain state applications primarily, the unified maximum stress/strain criterion is then subjected to further rationalization in the context of transversely isotropic materials by eliminating the treatments that undermine the objectivity of the failure criterion. The criterion is then applied based on the maximum and minimum direct stresses, the maximum transverse shear stress and the maximum longitudinal shear stress as the invariants of the stress state, instead of the conventional stress components directly.

Primordial Black Holes as Dark Matter: Recent Developments

Although the dark matter is usually assumed to be made up of some form of elementary particle, primordial black holes (PBHs) could also provide some of it. However, various constraints restrict the possible mass windows to 1016–1017 g, 1020–1024 g, and 10–103 M⊙. The last possibility is contentious but of special interest in view of the recent detection of black hole mergers by LIGO/Virgo. PBHs might have important consequences and resolve various cosmological conundra even if they account for only a small fraction of the dark matter density. In particular, those larger than 103 M⊙ could generate cosmological structures through the seed or Poisson effect, thereby alleviating some problems associated with the standard cold dark matter scenario, and sufficiently large PBHs might provide seeds for the supermassive black holes in galactic nuclei. More exotically, the Planck-mass relics of PBH evaporations or stupendously large black holes bigger than 1012 M⊙ could provide an interesting dark component.

Embedded Spherical Microlasers for In Vivo Diagnostic Biomechanical Performances

In this article, we propose to use spherical microlasers that can be attached to the surface of bones for in vivo strain monitoring applications. The sensing element is made of mixing polymers, namely, PEGDA-700 (Sigma Aldrich, St. Louis, MO) and Thiocure TMPMP (Evan Chemetics, Teaneck, NJ) at 4:1 ratio in volume doped with rhodamine 6G (Sigma Aldrich, St. Louis, MO) laser dye. Solid-state microlasers are fabricated by curing droplets from the liquid mixture using ultraviolet (UV) light. The sensing principle relies on morphology-dependent resonances; any changes in the strain of the bone causes a shift of the optical resonances, which can be monitored. The specimen is made of a simulated cortical bone fabricated with photopolymer resin via an additive manufacturing process. The light path within the resonator is found to be about perpendicular to the normal stress' direction caused by a bending moment. Therefore, the sensor measures the strain due to bending indirectly using the Poisson effect. Two experiments are conducted: 1) negative bone deflection (called loading) and 2) positive bone deflection (called unloading) for a strain range from 0 to 2.35 × 10−3 m/m. Sensitivity values are ∼19.489 and 19.660 nm/ε for loading and unloading experiments, respectively (percentage difference is less than 1%). In addition, the resolution of the sensor is 1 × 10−3 ε (m/m) and the maximum range is 11.58 × 10−3 ε (m/m). The quality factor of the microlaser is maintaining about constant (order of magnitude 104) during the experiments. This sensor can be used when bone location accessibility is problematic.