In this paper, the nonlinear elastic behavior of pericardium of human, canine, calf and ostrich was studied. For this purpose, the mechanical behavior was investigated from two viewpoints of the Cauchy and Green elastic materials. Firstly, the experimental data were fitted by Cauchy elastic stress equation. The results showed that the response of Cauchy elastic materials was not fitted with the experimental data appropriately. Secondly, the Green elastic materials were studied by assuming strain energy functions for the mechanical response of the samples. For this purpose, the exponential-exponential, power law-power law, and exponential-power law energy functions were investigated by mathematical programming. It was observed that all energy functions were fitted with the experimental data accurately, especially the power law-power law function. Finally, it was observed that the Green elastic materials theory was more appropriate for studying the mechanical behavior of pericardium by comparing the experimental and theoretical results.

The results of the research conducted by the researchers have shown that the application of electric current to the metal during deformation can lead to the improvement of the plasticity of the material. This method is known as forming with the help of electricity. In this article, the electro plastic effect on the strain behavior of a 6061-T6 aluminum alloy sheet has been investigated experimentally through the Uniaxial Tensile Test. For this purpose, Tensile Test samples were cut from a 6061-T6 aluminum alloy sheet with a thickness of 1 mm according to ASTM E8/E8M standard. Then it was examined in the state of no current and in the intensity of currents of 260, 360 and 460 amperes until the appropriate intensity of current is obtained. The results have shown that at a current intensity of 360 amps, the amount of extension in the sample increases compared to the state without current. In addition, a comparison was made between the results of two square and sinusoidal waveforms and it was shown that the sinusoidal waveform has a greater effect on increasing formability. The on and off time of the pulse was also investigated and it was determined that the maximum extension is created in the off time of 20 ms and the on time of 120 µs. Finally, the sample was annealed and the Test was repeated with the obtained parameters. The results showed that by applying an electric pulse with appropriate parameters, the formability of 6061-T6 aluminum samples is improved by 23%.

In the present research, damage mechanisms during room temperature Uniaxial Tensile Testing of two different modern high strength dual phase steels,DP780 and DP980, were studied. Detailed microstructural characterization of the strained and sectioned samples was performed by scanning electron microscopy (SEM). The results revealed that interface decohesion, especially at the triple junctions of ferrite-ferrite-martensite, was the most probable mechanism for void nucleation. Also, it was found that ductile fracture in these steels was nucleation controlled such that just before ductile fracture incidence, a high density of voids would nucleate or a sudden accelerated void nucleation could happen. Microscopic observations as well as statistical analysis confirmed this phenomenon. Moreover, damage analysis suggested that the void nucleation rate was higher in DP980 than DP780 steel. It seemed to be highly influenced by the morphology and distribution of martensite particles within the ferrite matrix.

The damage state of cross-ply composite laminates subjected to Uniaxial Tensile loading was examined in this study. Matrix cracking and induced delamination have been considered as the most common modes of damage in composite laminates. Using a micromechanical approach and based on Hashin variational principles, analysis of the stress field and reduced mechanical properties of a material with two symmetric and antisymmetric patterns have been examined. In order to improve the results obtained from the variational approach, the ply-refinement technique is used. Using the variational approach developed, the results of reduced mechanical properties have been compared to two methods: the homogenization method of 90°,layers cracked and the simultaneous analysis method of 90°,layers cracked. After, it has been used from an energy-based criterion to predict the initiation and propagation of Matrix cracking and induced delamination and also the saturation state of Matrix cracking. By comparing the analytical results and the numerical results obtained from the finite element software, it was observed that using the ply-refinement technique has a great impact on the increase in the accuracy of the results.

To respond to the external forces, adherent cells are reoriented from random orientation to an ordered and homogeneous one, regarding the applied strain direction. Furthermore, in subcellular scale, cytoskeleton and stress filaments with polarization generate inner contractile forces leading to a reorientation of the cell at a specific angle. In the present study, morphological changes of mesenchymal stem cells under cyclic strain toward myogenic differentiation were analyzed. Simulation of stem cell morphological changes using a nonlinear mechanical model (viscoelastic) is the innovative aspect of this research. To do so, mesenchymal stem cells with real size by the use of finite element method were designed in the Comsol software. Furthermore, time-dependent mechanical properties were applied. The Uniaxial cyclic strain is applied to the substrate, and the frequency of the strain was considered as one of the variables. The lying angle of the cell on the substrate was varied from 34 to 90° . Also, Young’ s modulus of the substrate and the role of strain alteration were investigated. The results revealed that the stress distribution on the cell and the nucleus are strongly dependent on the lying angle. The approximate angle in which the stress and strain is minimum was calculated about 70 degrees.

The study of the physical properties (geophysical methods) of rocks associated with its mechanical properties has recently received lots of attention. Recent studies show that geophysical methods especially the seismic and geoelectric methods are able to estimate the mechanical parameters and recognize their spatial variations, including anisotropy. Meanwhile, electrical and seismic methods are the most used one.Electrical measurement is one of the non-invasive geophysical methods commonly used by engineers working in various fields such as mining, geotechnical, civil, underground engineering as well as oil and gas mineral explorations. This method can be applied both in laboratory and in the field. Numerous scientists have focused on the relation between resistivity and porosity. However, there is a very limited study on the relation between the electrical resistivity and the rock properties apart from porosity.In this paper, changes in the electrical conductivity of rocks during a Uniaxial compression Test were investigated in laboratory. The Uniaxial compressive strength, elastic modulus, and density values of the samples were determined in laboratory. We installed special electrodes on seven nearly saturated core samples in order to measure the resistivity. Core samples had a 52-mm diameter and a 110-mm length. Two-electrode as well as four-electrode arrays were both used in resistivity monitoring in laboratory. Using a four-electrode array minimized the undesirable electrode polarization effects. In the four-electrode array, we used two non-polarizing Ag/AgCl electrodes mounted on the core sample. Our laboratory observations showed that there was not any electrode polarization effect. When we used a two-electrode array, the resistivity changes were less than 5 percent compared to a four-electrode array. In our laboratory investigation, we used different sedimentary core samples including sandstone, fossilioferous limestone and travertine. Maximum resistivity observed for the travertine core sample was less than 12 kohm. During the Uniaxial compressive Test, deformation measurements were made and the stress–strain curves were plotted. Tangent Young’s modulus values were obtained from stress–strain curves at a stress level equal to 50% of the ultimate Uniaxial compressive strength.Sandstone core samples showed a resistivity increase in the whole strain range. On the contrary, the fossiliferous limestone samples (thin section showed that the sample was composed of tiny calcium fossils in a fine aggregate of micrite cementation) showed a resistivity decrease in the whole strain range. Travertine and limestone showed an intermediate behavior (resistivity increased in the lower strain and it decreased in the higher range). In other words, the onset of new crack formation occurs well inside the quasi-linear part of the stress-strain curve. The quasi-linear portion of the stress-strain curve was the result of a competition between closure of one population of cracks, and the growth of new propagation of the existing cracks.Resistivity behavior during a Uniaxial compression load is closely related to the pores in the lower strain ranges and then to the new induced fractures in higher strains. Our results showed that the electrical resistivity may be a representative measure of the rock properties. Additionally, the effect of certain minerals on the rock’s resistivity must be taken into account. The results indicated that the rock structure had an important effect on the resistivity behavior during a mechanical loading.

Background & Aim: The orthodontic force-induced tissue strain produces local alterations in cellular and extracellular matrix reorganization, leading to the transformation and differentiation of cells. The present study was designed to investigate the influence of mechanical force on the CD90 expression of human mesenchymal stem cells (endometrial stem cells and dental pulp stem cells).Materials & Methods: The mesenchymal stem cells from passage 3-5 were seeded onto silicone membrane and cultured in medium with or without static mechanical stimulation (equiaxial and Uniaxial strains). After 2 weeks, cultured cells were analyzed for expression of CD90.Results: After 14 days in culture, immunfluorescence staining of cultured MSC demonstrated that mechanical stimulation of MSCs compared with control group, resulted in decreased CD90 expression.Conclusion: The decrease of CD90 expression in mechanically stimulated cultures compared to unstimulated control cultures suggests the possibility of differentiation of stem cells to other cells.

Strength measurement of rock requires Testing that must be carried out on Test specimens with particular sizes in order to fulfill Testing standards or suggested methods. Often, the coring process breaks up the weaker core pieces, and they are too small to be used in either index Tests or conventional strength Tests such as point load index (Is) and Brazilian Tensile strength (BTS). One of the index Tests to indirectly determine the rock strength is the block punch index (BPI) Test, which requires flat disc specimens without special treatment. This study aimed to evaluate the applicability of the BPI Test for predicting the Uniaxial compressive strength (UCS), BTS and IS of the sandstones by empirical equations. Also, we have compared the performance of the BPI and IS for predicting the UCS and BTS. It was experimentally shown that BPI is a reliable method for predicting the UCS, BTS and Is of the sandstones under study. Moreover, the results indicate that BPI could be utilized with same importance as Is for predicting the UCS, while predicting the BTS by Is appears to be more reliable than BPI.

Use of scrap tire rubber particles as aggregate in Portland-cement concrete is a suitable solution for the environmental hazards of waste tires being produced on a large scale. Tire rubber particles also reduce the brittle behavior of concrete due to their elasticity and plasticity. The effect of tire rubber particles on the mechanical properties of concrete is investigated in this study. Tire rubber particles were used in three (coarse, fine, and combined) groups to replace 12.5, 25, 37.5, and 50% of total aggregate volume in concrete. Cylindrical concrete specimens (15cm across and 30 cm high) were fabricated and cured. A compressive strain-control Test was performed on the specimens until failure occurred in large deformations. Results show lower strength and more ductile behavior for rubberized concrete compared to plain concrete specimens. Unlike in plain concrete, the failure state in rubberized concrete occurred gently and uniformly and did not cause any separation in the specimen. The crack width and its propagation velocity in rubberized concrete were lower than those in plain concrete.

Measuring of Uniaxial compressive strength (UCS) of intact rocks is necessary in many engineering projects. In deep well drilling for petroleum production or exploration drilling in deep tunnels, because depth wells, obtain suitable core samples for UCS Test is too extensive and sometimes impossible. Therefore indirect method for UCS determine (for example using rock particles) is common. One of these methods is known as indentation Test. In this Test an indenter that is hard penetrate in to rock particle which surrounded by resin is used. In this paper, 11 microcrystalline limestone block samples from carbonate Zagros formation outcrops is prepared and UCS Test in laboratory is performed. Then cores are crushed and 720 rock particle samples with 2, 3 and 4 millimeters size is prepared. Indentation Test with indenter 0.6, 0.8 and 1 millimeters diameter is done and critical transitional force (CTF) for each particles is determined. Empirical equation between UCS and CFT for different samples and indenter with R2³0.78 is suggested. Using multiple regression general equation between UCS, CFT, particle size (D) indenter diameter (I) with R2=0.85 is proposed. Verification of the proposed equations with 135 indentation Tests on 3 microcrystalline limestone samples and comparing measuring UCS in laboratory with estimate UCS are evaluated. This comparison showed that 88% they are similar.