Biaxial Coefficient Research Articles

Use of the biaxial coefficient in determining life for a combination of cyclic bending and torsion of bronze RG7

Use of the biaxial coefficient in determining life for a combination of cyclic bending and torsion of bronze RG7

Liquid Crystal Elastomer Metamaterials with Giant Biaxial Thermal Shrinkage for Enhancing Skin Regeneration.

Liquid crystal elastomers (LCEs) are a class of soft active materials of increasing interest, because of their excellent actuation and optical performances. While LCEs show biomimetic mechanical properties (e.g., elastic modulus and strength) that can be matched with those of soft biological tissues, their biointegrated applications have been rarely explored, in part, due to their high actuation temperatures (typically above 60°C) and low biaxial actuation performances (e.g., actuation strain typically below 10%). Here, unique mechanics-guided designs and fabrication schemes of LCE metamaterials are developed that allow access to unprecedented biaxial actuation strain (-53%) and biaxial coefficient of thermal expansion (-33125ppmK-1 ), significantly surpassing those (e.g., -20% and -5950ppmK-1 ) reported previously. A low-temperature synthesis method with use of optimized composition ratios enables LCE metamaterials to offer reasonably high actuation stresses/strains at a substantially reduced actuation temperature (46°C). Such biocompatible LCE metamaterials are integrated with medical dressing to develop a breathable, shrinkable, hemostatic patch as a means of noninvasive treatment. In vivo animal experiments of skin repair with both round and cross-shaped wounds demonstrate advantages of the hemostatic patch over conventional strategies (e.g., medical dressing and suturing) in accelerating skin regeneration, while avoiding scar and keloid generation.

Approximation of Heat Dissipation-Crack Rate Curve for Fatigue Crack in Stainless Steel

The experimental and theoretical analysis of thermodynamical peculiarities of heat flux at the fatigue crack tip during its propagation was made in presented work. The goal is to elucidate the relation between heat flow at the crack tip and kinetic of fatigue crack propagation for different loading conditions. The plane specimens with notch made from stainless steel (AISI 304) were studied. There were two types of specimens for uniaxial loading and one type for biaxial loading. A heat dissipation during fatigue crack propagation was measured by simultaneous use of contact and noncontact techniques. The samples were subject to cyclic loading with constant stress amplitude and different biaxial coefficients. The functional dependence between crack propagation and heat flow at the crack tip was received by experiment measurement and analytical calculation. This relation depends on only type of material and righty for all fracture mode.

The experimental and theoretical study of heat dissipation at fatigue crack tip under biaxial loading

In this work we have studied both experimentally and theoretically the evolution of a heat flux at a fatigue crack tip during biaxial loading. The goal is to elucidate the dependence of the heat flux on the crack growth rate for different loading conditions. Tests were carried out on titanium alloy (Grade 2) and stainless steel (AISI 304) flat samples weakened by notches to initiate fatigue cracks at their centers. The dissipated thermal energy was monitored using an infrared camera and the original Seebeck effect-based contact heat flux sensor. Samples were subjected to constant stress amplitude cyclic loading at different biaxial coefficients. The experimental results obtained in this study confirmed our previous conclusions about two stages of energy dissipation at the tip of a fatigue crack propagating in the Paris regime. At the first stage, the crack growth rate is proportional to the heat flux multiplied by the crack length. The second stage is characterized by a traditional linear relationship between heat flux and crack growth rate. The theoretical approach proposed here for calculating energy dissipation at a fatigue crack tip is based on the relation between elasto-plastic and elastic strain fields near a crack tip in terms of Young’s and secant plasticity moduli. This relation was examined by applying a digital image correlation (DIC) method to measure a strain field and through numerical simulations. DIC can also be used to determine the size of plastic area near a fatigue crack tip.

The experimental study of heat dissipation during fatigue crack propagation under biaxial loading

The work is devoted to experimental study of heat flow evolution at the fatigue crack tip during biaxial loading. The plane samples of titanium alloy Graid-2 with thick of 1 mm were weakened by notch to initiate fatigue crack at the center of samples. Infrared thermography and the contact heat flux sensor based on the Seebeck effect are used to monitor the dissipated thermal energy. During tests the samples were subjected to cyclic loading of 10 Hz with constant stress amplitude and different biaxial coefficient. The experimental results confirm the previous conclusions of authors about two regime of energy dissipation at fatigue crack tip. The heat dissipation curve can be divided in two stages. Under the first stage the power of heat flux is proportional to the multiplication of the crack rate by its length. In the second stage is characterized by classical linear relationship between crack rate and heat flux rom the crack tip. The qualitative correspondence of the energy approach to the classical representation based on the stress intensity factor was shown.

Experimental and theoretical analysis of heat flux at fatigue crack tip under mixed mode loading

The work is devoted to experimental and theoretical study of heat dissipation at the fatigue crack tip during mixed mode loading. The plane samples of stainless steel (AISI 304) were weakened by notch to initiate fatigue crack. There were two types of samples for uniaxial loading and biaxial loading. Infrared thermography and the contact heat flux sensor based on the Seebeck effect were used to measure the dissipated thermal energy. The samples were subject to cyclic loading with constant stress amplitude and different biaxial coefficients. The experimental results confirmed the hypothesis about two stages of heat dissipation at fatigue crack tip under Paris regime. At the first stage, the power of heat flux is proportional to the product of the crack rate by the crack length. The second stage is characterized by a traditional linear relationship between the crack rate and the heat flux. The theoretical approach to calculate dissipation energy at fatigue crack tip was obtained. This technique based on link between the elastic-plastic and elastic strain fields at crack tip using the coupling between Young’s modulus and the secant plasticity modulus.

The experimental and theoretical study of plastic deformation in the fatigue crack tip based on method of digital image correlation

This work is devoted to the experimental study of strain distribution at crack tip using digital image correlation technique. The real strain fields were compared with an elastic solution for verification of a hypothesis about link of the elastic-plastic and elastic strain fields at crack tip using the coupling between Young’s modulus and the secant plasticity modulus. The precracked plane specimens of titanium alloy VT1-0 with a thick of 1 mm were used in experimental program. The method of digital image correlation based on system StrainMaster was used for measurement the plastic deformation with spatial resolution up to 1 mkm. The strain field was obtained for different crack length and different biaxial coefficient was obtained using biaxial testing machine Biss BI-00-502. Numerical simulation of deformation fields at the fatigue crack tip was done. A qualitative correspondence between the theoretical, calculation and experimental results has been shown.

The heat dissipation at fatigue crack tip under mix mode loading

The cruciform plane specimens of titanium alloy VT1-0 with a thick of 1 mm were tested to study temperature evolution under fatigue crack propagation. The original contact sensor of heat flow and method of infrared thermography were used to analyze the dissipated energy from crack tip during fatigue tests. A series of experiments was carried out to study the propagation of a fatigue crack under biaxial loading with different biaxial coefficient. It has been shown that heat dissipation caused by fatigue crack propagation under Paris regime can be divided into two stages both under uniaxial and biaxial loading conditions.