International Journal of Mechanical and Materials Engineering最新文献

In the present study, the effect of cone angle of tool pin on the mechanical properties and microhardness properties of aluminum alloy AA6061-T6 specimens is investigated for three processes of SFSW, symmetric DFSW, and asymmetric DFSW. In each of the mentioned welding processes, tools with 5 different conical angles of 0, 5, 10, 15, and 20° are used. In these three welding processes, the mechanical properties of the final welded joint with conical tools have been enhanced noticeably compared to the tool with simple cylindrical pins (0° angle). Based on the obtained results, it was found that the joints obtained from asymmetric DFSW, symmetric DFSW, and SFSW had the best mechanical properties, respectively. The optimum cone angles for tool pin in SFSW, symmetric DFSW, and asymmetric DFSW processes were equal to 15, 10, and 10°, respectively. In addition, it was concluded that the welded specimen through the asymmetric DFSW with the cone angle of 10° attained the closest mechanical properties to the base (parent) metal. The parameters of YS, UTS, and E% in this sample were 78.3%, 84.8%, and 86.4% of the base sample, respectively.

Calcium fluoride (CaF₂) is widely used for different bio applications ranging from biomedical imaging to cell labeling. The biocompatible properties of CaF₂ combined with superior mechanical properties of titanium alloy makes it a perfect choice for orthopedic and dental implants. A dip-coating process was employed to develop a thin film of CaF₂ coating on Ti6Al4V material with an intermediate thin layer of shellac (natural resin). The developed coating was subjected to X-ray powder diffraction method (XRD) and scanning electron microscopy (SEM) to evaluate the surface characteristics. The dip-coated implant material was also subjected to mechanical property evaluation, dissolution behavior study, and corrosion behavior study. In vitro study of the developed implant material was also carried out to assess the biocompatibility. The obtained results suggest use of CaF₂ coating developed by this method for producing biocompatible orthopedic implants.

Regional mechanics of the heart is vital in the development of accurate computational models for the pursuit of relevant therapies. Challenges related to heart dysfunctioning are the most important sources of mortality in the world. For example, myocardial infarction (MI) is the foremost killer in sub-Saharan African countries. Mechanical characterisation plays an important role in achieving accurate material behaviour. Material behaviour and constitutive modelling are essential for accurate development of computational models. The biaxial test data was utilised to generated Fung constitutive model material parameters of specific region of the pig myocardium. Also, Choi-Vito constitutive model material parameters were also determined in various myocardia regions. In most cases previously, the mechanical properties of the heart myocardium were assumed to be homogeneous. Most of the computational models developed have assumed that the all three heart regions exhibit similar mechanical properties. Hence, the main objective of this paper is to determine the mechanical material properties of healthy porcine myocardium in three regions, namely left ventricle (LV), mid-wall/interventricular septum (MDW) and right ventricle (RV). The biomechanical properties of the pig heart RV, LV and MDW were characterised using biaxial testing. The biaxial tests show the pig heart myocardium behaves non-linearly, heterogeneously and anisotropically. In this study, it was shown that RV, LV and MDW may exhibit slightly different mechanical properties. Material parameters of two selected constitutive models here may be helpful in regional tissue mechanics, especially for the understanding of various heart diseases and development of new therapies.

One of the problem areas of fluid flow in the turbomachine is its inlet region, manifested by flow distortions due to the induced fluid swirl accompanied by improper flow incidence onto the impeller. Further, the hub forms one of the main components of many of the turbomachines and it is found that there has not been significant study on geometrical modifications of the same in centrifugal fans for augmented performance. This is partially due to designers trying to reduce the cost of the overall machine.

There is a scope for detailed parametric study and the present work involves an exploration of flow behavior by parametric variation of hub geometry in terms of both its shape and size.

Experiments are carried out in order to determine the importance of hub with different size and shapes. The geometric models of hemi-spherical and ellipsoidal hubs are considered for the analyses in the present study.

An optimized ellipsoidal hub configuration is found to yield a relative improvement of about 7.5% for head coefficient and 7.7% increase in relative theoretical efficiency over the hub-less base configuration. Finally, correlations are developed for the optimized hub shape configurations.

It is revealed from experimental analysis that hub plays a vital role in streamlining the flow at the inlet to the centrifugal fan and augments its performance.

The Poisson’s ratio, a property which quantifies the changes in thickness when a material is stretched and compressed, can be determined as the negative of the transverse strain over the applied strain. In the scientific literature, there are various ways how strain may be defined and the actual definition used could result in a different Poisson’s ratio being computed. This paper will look in more detail at this by comparing the more commonly used forms of strain and the Poisson’s ratio that is computable from them. More specifically, an attempt is made to assess through examples on the usefulness of the various formulations to properly describe what can actually be observed, thus providing a clearer picture of which form of Poisson’s ratio should be used in analytical modelling.

Laser surface hardening is rapidly growing in industrial applications due to its high flexibility, accuracy, cleanness and energy efficiency. However, the experimental process optimization can be a tricky task due to the number of involved parameters, thus suggesting for alternative approaches such as reliable numerical simulations. Conventional laser hardening models compute the achieved hardness on the basis of microstructure predictions due to carbon diffusion during the process heat thermal cycle. Nevertheless, this approach is very time consuming and not allows to simulate real complex products during laser treatments. To overcome this limitation, a novel simplified approach for laser surface hardening modelling is presented and discussed. The basic assumption consists in neglecting the austenite homogenization due to the short time and the insufficient carbon diffusion during the heating phase of the process. In the present work, this assumption is experimentally verified through nano-hardness measurements on C45 carbon steel samples both laser and oven treated by means of atomic force microscopy (AFM) technique.

Ductile failure of polymeric samples weakened by circular arc cracks is studied theoretically and experimentally in this research. Various arrangements of cracks with different arc angles are considered in the specimens such that crack tips experienced the mixed mode I/II loading conditions. Fracture tests are conducted on the multi-cracked specimens and their fracture loads are achieved. To provide the results, the equivalent material concept (EMC) is used in conjunction of dislocation method and a brittle fracture criterion such that there is no necessity for performing complex and time-consuming elastic-plastic damage analyses. Theoretical and experimental stress intensity factors are computed and compared with each other by employing the fracture curves which demonstrate the appropriate efficiency of proposed method to predict the tests results.

The aim of the present investigation is to examine the memory-dependent derivatives (MDD) in 2D transversely isotropic homogeneous magneto thermoelastic medium with two temperatures. The problem is solved using Laplace transforms and Fourier transform technique. In order to estimate the nature of the displacements, stresses and temperature distributions in the physical domain, an efficient approximate numerical inverse Fourier and Laplace transform technique is adopted. The distribution of displacements, temperature and stresses in the homogeneous medium in the context of generalized thermoelasticity using LS (Lord-Shulman) theory is discussed and obtained in analytical form. The effect of memory-dependent derivatives is represented graphically.

This is a study of the degradation of amorphous silicon solar cells. The study accessed structural defects and the mechanical stress of solar cells at nanoscale level. Interface morphology, deformation, and internal delamination of the cells were analyzed. Adequate analysis of roughness parameters was performed to investigate the state of degradation of the amorphous silicon solar modules (a-Si:H) used in this study. Roughness parametric test is necessary in thin film solar cells production process because it is used to quantify the relationship that exists between roughness parameters and electrical efficiencies of solar cells. However, in this study, a roughness analysis was not only performed to quantify the performance of the a-Si:H module but to also compliment their mechanical degradation analysis. Roughness indicators such as root means square (RMS) roughness and average roughness were acquired from line profiles. Measurements were taken with scanning probe microscope (SPM) and PeakForce Quantitative Nanomechanical (QNM) technique was used through the cross sectional area of the analyzed samples. The method was validated with adhesive force and deformation analyses; it was established that high roughness values result from mechanical degradation. Results from the roughness parameters and the mechanical degradation analysis were further observed from in situ measurements and these showed good compatibility. The benefit of this technique is that it provides a good procedure for the evaluation of mechanical degradation without destroying any part of the intrinsic layers in a-Si:H modules.