Papers by Keyword: Internal Stress

Abstract: The evolutions of physical properties of composites during the curing process of the carbon fibre reinforced resin composite, such as density, modulus, coefficient of thermal expansion, specific heat capacity and thermal conductivity, were analyzed and those evolutions were introduced into the numerical simulation. The new approach to construct the curvilinear coordinate system by streamline equation of steady flow was proposed with the complex curved structure composite as the study object. By using the finite-element method and building the curvilinear coordinate system, the distribution of internal temperature, degree of cure, internal stresses and evolutions of physical properties during the curing process of the composite skin plate of a light aircraft wing were calculated. The deformation of the skin plate caused by the uneven distributions of temperature field and cure degree field, anisotropic thermal expansion coefficients and volumetric shrinkage of resin were calculated in the same model. From the numerical simulation results, it can be concluded that the curing process will be more reasonable and more accurate when the evolutions of physical properties of composites are adopted and the curvilinear coordinate system constructed by streamline equation of steady flow is fully applicable to finite element analysis of composite curved structure.

Abstract: Arrangement of internal stresses in deformed austenitic steel is studied. The internal stresses are determined using parameters of bending extinction contours observing on electron microscope images of steel.

Abstract: The excess density of dislocations and internal stresses in local places of all polycrystal grain are determined. In work the methods of bending extinction contours observed by TEM is used to determine internal stresses of the deformed material. Thus depending on the deformation nature in each case components of elastic and plastic deformations or only plastic deformation was considered. The paper discusses the results of distribution of excess dislocation density and internal stresses within the grains of the austenitic steel deformed by tension (ε = 25%).

Abstract: An on-chip suite of MEMS-based mechanical testing structures has been developed to extract the mechanical properties of freestanding thin films under tensile loading. The working principle relies on the use of high tensile internal stress within an actuator beam to deform a specimen beam made of another material owing to the etching of an underlying sacrificial layer. In order to control the deformation rate imposed during the etching process, the rectangular shape of actuator beam design has been recently upgraded to a tapered shape. The deformation rate is estimated from the modelling of the two extreme cases defining the upper and lower limit. The proof of concept is demonstrated experimentally from the investigation of the mechanical response of 100 nm-thick freestanding copper thin films deposited by e-beam evaporation.

Abstract: Micromechanical simulations of polycrystalline zirconia using the finite element method are performed in order to obtain the stresses at the grain scale of a zirconium oxide layer, since these microstresses are important for damage prediction of the layer and then oxidation kinetics. The crystallographic texture of the layer of monoclinic zirconia is taken into account. The results show that even under high compressive macroscopic stresses, the microstresses can contribute to lateral cracking promoted by the presence of tetragonal zirconia.

Abstract: The rebound hammers of the Schmidt system belong among the non-destructive testing methods that are used for determining compressive strength of building materials, most often concrete and rocks. Calibration relations between the rebound number and compressive strength must be available to determine the compressive strength. Calibration relations are determined on the basis of destructive and non-destructive tests of test specimens. This paper deals with the effects of internal compressive stress in calcium silicate bricks on measurement results obtained using the L-type Schmidt hammer. Based on the obtained information, in order to process calibration relations, it is recommended to apply such force to the test specimens, which corresponds to the internal compressive stress 10-15% of the final compressive strength. We do not recommend measuring on firmly supported bricks only.

Abstract: A new rationale to assess the work-hardening locus for pre-rolled sheets is described based on the realization that since the internal stresses necessarily sum to zero, the mean dislocation density remains the same upon re-pull in the rolling direction. Thus the 0.2 % yield stress as function of thickness strains results in an estimate of the stress-strain relation during rolling. Under plane strain, the thickness strain is negative to that of extension and hence the deduced rolling locus is compared to that of extrapolated tensile one of the start sheet. This comparison indicates that the onset of Stage IV occurs when volume fraction of point defects produced attains about 2 %.

Abstract: In this paper, substrate curvature method was adopted and a theory model based on Stoneys formula was built for obtaining the internal stress of SU-8 film. The effect of substrate diameter, film thickness and post-baked temperature on substrate curvature ratio was investigated by ANSYS simulation. The analytical result shows that post-baked temperature is the main effect factor on internal stress of SU-8 film. In addition, internal stresses of SU-8 at three different post-temperatures (55°C, 70°C and 85°C) are measured. The results show that the experimental results greatly agreed with simulation analytical results. It means the internal stress of SU-8 film can be accurately described by the theory model, which provides a basis for the quantitative analysis of the internal stress in SU-8 film.

Abstract: The aim of this paper is to calculate and compare both tangential and normal internal stresses in contacting area of two spherical bodies in contact. The results of these calculations have a practical use in further research of coefficient of friction in relation to the surface roughness asperities of contacting bodies.

Abstract: The cyclic deformation behavior and fatigue characteristics of a new austenitic manganese steel with composition FeMn18Cr7C0.8N0.2 (wt%) have been explored and analyzed based on the partition of hysteresis loops linked with microstructure by low cycle testing in the total strain amplitudes 0.3% - 1.0%. The new N+C austenitic manganese steel exhibited immediate cyclic softening for small strain amplitude and initial hardening at the onset of fatigue life followed by softening for medium and high strain amplitudes. For low and high strain amplitudes the evolution of internal stress and effective stress partitioned from the hysteresis loop with the prolonged cycles both corresponded to the change in the total stress amplitudes. With the exception of 316LN0.2 austenitic stainless steel, the effective stress and internal stress made a contribution to the cyclic deformation behavior with similar effect. The markedly improved contribution of effective stress in the new N+C austenitic manganese steel was attributed to the enhanced short range order caused by N+C alloying whereas the decreasing of effective stress with the number of cycles was because of this broken short range interaction. TEM observations showed that the significantly increased planar dislocation structures due to the presence of N+C were responsible for the strong tendency to cyclic softening, in association with the decrease of effective stress and internal stress simultaneously. Moreover the fatigue short crack could be observed on the fractured sample surface at high strain amplitude.