Shape Of Load-displacement Curve Research Articles

Evolution Rules of Fractures for Mudstone under Compression Shear Load and the Fractal Characteristics of Broken Blocks

Failure of rocks is commonly induced by compressive and shear coupling loading. Knowledge of the mechanism and process of deformation and failure of rocks under compressive shear loading condition is an important basis for the study of stability in rock engineering. Based on the nonlinear fractal theory, it is possible to examine the evolution rules of fractures in mudstone under compression shear load and the fractal characteristics of broken blocks using the shear compression test with variable angles of mudstone specimens in natural conditions. This research shows that the cohesion and friction angle parameters of rock samples are achieved by draw Mohr’s strength envelope according to the test date of variable‐angle shear compression test. It also shows that the shape of load‐displacement curves of rocks can be divided into four stages: compaction, elastic, plastic, and fracture, and the curve can accurately represent the transformation and breakage characteristics of rock during shear fracture. And the distribution of broken blocks shows a strong statistical resemblance to the fractal distribution, and the fractal dimension is able to reflect the distribution characteristics of broken blocks. With increasing the shear angle, the fractal dimension of broken blocks decreases in a logarithmic relationship.

Investigation of mechanical behavior of energy absorbers in expansion and folding modes under axial quasi-static loading in both experimental and numerical methods

In this paper, a new form of energy absorbing structures has been introduced which energy absorbing is occurred during a combined process. The structure consists of a thin-walled aluminum matrix and a thin-walled steel punch. Energy is absorbed as the matrix gets expanded followed by simultaneous matrix and punch folding. In order to demonstrate the effectiveness of absorbent introduced, many samples of each type were fabricated and tested. In one case, it was found that, the new structure tends to absorb up to 32% more energy than sum of the energy absorbed by its individual parts. Also, the energy absorption properties and the parametric study were simulated using finite element code LS-Dyna. The results showed that among different section geometries, structures with rectangular section have the lowest energy absorption and the highest crush force efficiency; by increasing the number of sides of the cross section the absorbed energy increased and crush force efficiency is decreased. In addition, increasing the thickness of the punch leads to increased energy absorption. Also, it was found that, selecting an appropriate thickness for the punch, one can predict overall shape of load-displacement curve and maximum force location for the combined structure.

Effects of binder addition on the surface generation mechanism of WC/Co during high spindle speed grinding (HSSG)

High spindle speed grinding (HSSG) of WC/Co and binderless WC was conducted to study the effects of binder addition on surface generation mechanism. To help to explain the role of Co binder, Vickers-indentation and nano-indentation test were also conducted on the polished WC/Co and binderless WC workpiece. The indentation results showed that even though the addition of Co binder could obviously improve the toughness of bulk materials, non-uniform surface plastic deformation can be induced by the varied hardness of composing phases in nanoscale, indicated by the shape of load-displacement curves at low loads. Moreover, except for the scratching grooves and feed marks, the machined WC/Co surface was covered by randomly distributed micro-pits resulted from the dislodgement of hard particles in comparison with the binderless WC. Fast Fourier Transform (FFT) analysis confirmed the obvious contribution of binder addition to the spatial frequency at 148.1 1/mm than the feed component. Moreover, the results showed that the machined surface experienced no evident oxidation with minimum quantity lubrication, but a deformed surface layer formed under the dynamic pressure of the diamond grits during grinding.

Nová metoda stanovení mikromechanických vlastností vaječné skořápky

The paper describes a new approach for determination of mechanical properties of hen’s eggshell. The suitability and applicability of a Berkovich indentation is discussed. The eggshells were tested in the area surrounding equator line. The deformation modes active during indentation have been examinined from the shape of load-displacement curves. According to measured dependencies, the eggshel shown an viscous-elastic deformation.The values of Young’s modulus E obtained from radial and tangential directions did not vary significantly. This fact shows on isotropic nature of eggshell structure. It was found that values of E do not significantly change neither around the cir­cum­fe­ren­ce of the equator. The values obtained within this research correspond to values reported in literature and obtained on macroscopic samples. Nanoindentation was found to be a precise and powerful tool, suitable for determining local variations of mechanical properties of eggshells.