Papers by Keyword: Unloading

Abstract: Mechanical loading and unloading of silicon is a characteristic feature of grinding and diamond turning processes. Such rapid loading and unloading induces damage and phase transformations. While, indentation tests are often used to study such normal loading and unloading via characteristic events in the force-depth plot, such tests involve only normal loading and lack tangential loading. A better alternative is scratch test, both constant and varying depth ones, involving normal and tangential loading on the scratching tool; this better simulates conditions of machining, or grinding. In this research, the mechanical load/unload behavior response of silicon is studied under scratching conditions by comparing increasing and decreasing depth scratch behaviour. In-situ force responses show that after ductile-brittle transition occurs, higher forces, at a given scratch depth, are required to deform the material during increasing depth scratching for a given depth than in decreasing depth scratch. Large surface and sub-surface damages with the presence of radial, median, and lateral cracks are seen to make the material weaker, ahead of the advancing tool, in decreasing depth scratch. Raman intensity ratio of amorphous silicon (a-Si) to nanocrystalline silicon (nc-Si) shows that high amorphization of silicon occurs during increasing depth scratching than decreasing depth. Using such force-depth plots an attempt is made to compare the normal loads while indenting and scratching. This study can help optimize the processing of silicon by grinding and diamond turning.

Abstract: This paper studies the problem of the relative area changing on a decrease of the load applied to the joint of roughness surfaces. The penetration of a rigid rough sphere (indenter) into the elastic hardenable half-space is initially considered, then the elastic crater restoring by unloading is considered. To defining elastic-plastic material, Hollomon’s power law is used. To describe a contact of a rigid rough surface with an elastic plastic half-space, the discrete model of a rough surface is used. Microasperities are represented as a set of identical spherical segments, the height distribution of which corresponds to the bearing profile curve of the real surface. The dependence the dimensionless force elastic-geometric parameter F_q on a relative amount of indentation ε at loading and the dependence of analogous parameter F_qe on amount of ε-Dε at unloading are obtained. The relations of relative contact areas h and h_e on dimensionless loading F_q and F_qe at loading and unloading for different values of a hardening exponent n and parameter are given. The obtained results are of practical importance for the performance prediction of fixed machine elements’ joints at the design stage, in particular for tightness supply of flange couplings and high pressure vessels seals.

Abstract: A 2D homogeneous orthotropic constitutive model of tensile and shear fracture in timber based on fixed smeared crack approach has been developed and implemented in ATENA^® finite element software. The model captures (1) elastic and inelastic behavior in small deformations range, (2) material orthotropy, both in linear and non-linear range, (3) cracking across or along fibers, and (4) behavior under unloading/reloading. In this contribution we present model validation through numerical simulations of compact tension shear (CTS) tests of Radiata Pine timber.

Abstract: In this report, we discussed the physical properties of encapsulated Methylene Blue (MB) by Silica Nanoparticles (SiNPs) intended for photodynamic therapy application. The aim of this discussion is to determine the suitable concentration of MB which can be delivered to the target area. Results shows that the size of SiNP is not affected by the change in MB concentration from out-diffusion process even when the concentration of loaded MB were reduce by more than 50 percent. The applicability of the encapsulated MB in SiNP was demonstrated on Red Blood Cells (RBCs) and the results were compared to those obtained from naked MB.

Abstract: In this paper, a model that the profiled bar cantilever scaffold with the hoisting unloading rope is created, utilizing the software sap2000.Analyzing of load-bearing of very parts of the scaffold. Calculating bearing capacity of the hoisting wire rope and the bearing capacity of hoisting rings. Put forward the design method of unloading wire rope and detailed construction requirements solution of scaffold.

Abstract: The mechanical properties of rock mass under unloading conditions are essentially different from that under loading conditions. Triaxial compression tests and unloading confining pressure tests are conducted, and test results show that unloading failure is more brittle, and rock samples suffer more damage under unloading failure. The larger the initial confining pressure is, the easier of unloading failure is occurred. The increasing or decreasing values of rock deformation modulus under unloading conditions are within 10% of rock triaxial compressive strength. Unloading failure leads to deterioration of rock deformation modulus, which decreases gradually with confining pressure decreasing, and the decrease rates get bigger and bigger with unloading ratio of confining pressure increasing. Deformation modulus is only 24-34% of that under loading condition when rock strength goes down to residual strength.

Abstract: The extensive development vertical joints is one of the major features in the loess region. The joint destroyed the loess slope integrity, reduces the slope stability. First of all, through the field investigation and analysis the loess joint development characteristics, joint with slope tendency towards a big angle oblique, joints control slope trend. Secondly, according to the different regional slope stress analysis, tableland soil area is mainly by collapsibility tension, soil in the slope zone mainly by horizontal thrust produced by unloading effect, the slope area joint development is divided into collapsibility joint development zone, tension joint development zone, compression joint development zone and the excavation unloading joint development zone.

Abstract: This paper performed numerical simulations of effects of unloading on occurrence of rock lateral cracks by using the numerical analysis software. The results indicate that the probability of median cracks and Hertz cracks occurrence was decreased due to the residual stress caused by stress mismatch during unloading, while the probability of lateral cracks occurrence was increased. The lateral cracks were tended to occur with the increasing of the amount of unloading and confining pressure. And the initiation direction of lateral cracks is more parallel to the rock surface, although the initiation direction became the same at the end. The relative positions of lateral cracks occurred were more concentrated during unloading process under the same confining pressure.

Abstract: Faults are the commonly encountered large geological discontinuities in hard rock masses, many severe open pit slope failures are found to be closely associated with the faults presence nearby. Open-pit slope takes shape gradually as a rock unloading process accompanied by geostress redistribution, especially in a slope containing a fault. The finite difference code (UDEC) was employed as the analytical method in this paper and coulomb slip model was utilized to describe the properties of fault provided by UDEC. Parametric analysis has identified both the fault dips and fault locations relative to the open pit slope to be really critical for the open pit slope stability. The relationship of crest displacements, safety factor varying with these fault parameters was established. The distribution of plastic zone and displacement was graphically presented and the mechanisms such effects were discussed. These results offer a guideline in support design for an open-pit slope containing a fault.

Abstract: Loading behavior studies on FRP-concrete interface are refined enough. Because of the complexity of the problem, there exist relatively few unloading behavior studies. Occurrence mechanism of unloading needs to be clarified. Through a combination of theory and finite element method, this paper studied the unloading behavior involved in interfacial failure process under an exponential softening law, clarified when and where unloading occurred and estimated the effect of unloading.