Showing papers in "International Journal of Mechanical and Materials Engineering in 2021"

Injection-molded natural fiber-reinforced polymer composites–a review

Abstract: For the last couple of decades, researchers have been trying to explore eco-friendly materials which would significantly reduce the dependency on synthetic fibers and their composites. Natural fiber-based composites possess several excellent properties. They are biodegradable, non-abrasive, low cost, and lower density, which led to the growing interest in using these materials in industrial applications. However, the properties of composite materials depend on the chemical treatment of the fiber, matrix combination, and fabrication process. This study gives a bibliographic review on bio-composites specially fabricated by the injection-molding method. Technical information of injection-molded natural fiber reinforcement-based composites, especially their type and compounding process prior to molding, are discussed. A wide variety of injection-molding machines was used by the researchers for the composite manufacturing. Injection-molded composites contain natural fiber, including hemp, jute, sisal, flax, abaca, rice husk, kenaf, bamboo, and some miscellaneous kinds of fibers, are considered in this study.

CFD simulations of gearboxes: implementation of a mesh clustering algorithm for efficient simulations of complex system’s architectures

Abstract: In the last decade, computer-aided engineering (CAE) tools have become a determinant factor in the analysis of engineering problems. In fact, they bring a clear reduction of time in the design phase of a new product thanks to parametrical studies based on virtual prototypes. The application of such tools to gearboxes allowed engineers to study the efficiency and lubrication inside transmissions. However, the difficulties of handling the computational domain are still a concern for complex system configurations. For this reason, the authors maintain that it is fundamental to introduce time efficient algorithms that enable the effective study of any kind of gear, e.g., helical and bevel configurations. In this work, a new mesh handling strategy specifically suited for this kind of studies is presented. The methodology is based on the Global Remeshing Approach with Mesh Clustering (GRAMC) process that drastically reduces the simulation time by minimizing the effort for updating the grids. This procedure was tested on spur, helical, and bevel gears, thus demonstrating the flexibility of the approach. The comparison with experimentally measured power losses highlighted the good accuracy of the strategy. The algorithm was implemented in the opensource software OpenFOAM®.

Experimental investigation on a novel approach for laser surface hardening modelling

Abstract: 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.

Plane wave in non-local semiconducting rotating media with Hall effect and three-phase lag fractional order heat transfer

Abstract: This paper deals with the propagation of the plane wave in a nonlocal magneto-thermoelastic semiconductor solid with rotation. The fractional-order three-phase lag theory of thermoelasticity with two temperatures has been applied. When a longitudinal wave is incident on the surface z = 0, four types of reflected coupled longitudinal waves (the coupled longitudinal displacement wave, the coupled thermal wave, coupled carrier density wave, and coupled transverse displacement wave) are identified. The plane wave characteristics such as phase velocities, specific loss, attenuation coefficient, and penetration depth of various reflected waves are computed. The effects of two temperatures, non-local parameter, fractional order parameter, and Hall current on these wave characteristics are illustrated graphically with the use of MATLAB software.

Friction and contact temperature in dry rolling-sliding contacts with MoS2-bonded and a-C:H:Zr DLC coatings

Abstract: Gearboxes are usually lubricated with oil or grease to reduce friction and wear and to dissipate heat. However, gearbox applications that cannot be lubricated with oil or grease, for example in the space or food industry, are commonly lubricated with solid lubricants. Especially solid lubricants with a lamellar sliding mechanism like graphite and molybdenum disulfide (MoS2) or diamond-like carbon (DLC) coatings can enable very low coefficients of friction. This study investigates the friction and temperature behavior of surface coatings in rolling-sliding contacts for the application in dry lubricated gears. In an experimental setup on a twin-disk test rig, case-hardened steel 16MnCr5E (AISI5115) is considered as substrate material together with an amorphous, hydrogenated, and metal-containing a-C:H:Zr DLC coating (ZrCg) and a MoS2-bonded coating (MoS2-BoC). The friction curves show reduced coefficients of friction and a significantly increased operating area for both surface coatings. Due to the sufficient electrical insulation of the MoS2-BoC, the application of thin-film temperature measurement-known from lubricated contacts-was successfully transfered to dry rolling-sliding contacts. The results of the contact temperature measurements reveal pronounced thermal insulation with MoS2-BoC, which can interefere the sliding mechanism of MoS2 by accelerated oxidation. The study shows that the application of dry lubricated gears under ambient air conditions is challenging as the tribological and thermal behavior requires tailored surface coatings.

Study of biaxial mechanical properties of the passive pig heart: material characterisation and categorisation of regional differences

Abstract: 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.

Experimental investigation into the effect of surface roughness and mechanical properties of 3D-printed titanium Ti-64 ELI after heat treatment

Abstract: The initial stability after implantology is paramount to the survival of the dental implant, and the surface roughness of the implant plays a vital role in this regard. The characterisation of surface topography is a complicated branch of metrology, with a huge range of parameters available. Each parameter contributes significantly towards the survival and mechanical properties of three-dimensional printed specimens. The purpose of this paper is to experimentally investigate the effect of surface roughness of three-dimensional printed dental implants and three-dimensional printed dogbone tensile samples under areal height parameters, amplitude parameters (average of ordinates), skewness parameters and mechanical properties. During the experiment, roughness values were analysed, and the results showed that the skewness parameter demonstrated a minimum value of 0.59%. The three-dimensional printed dental implant recorded the arithmetic mean deviation of the assessed profile with a 3.4-mm diameter at 43.23% and the three-dimensional printed dental implant with a 4.3-mm diameter at 26.18%. Samples with a complex geometry exhibited a higher roughness surface, which was the greatest difficulty of additive manufacturing when evaluating surface finish. The results show that when the ultimate tensile stress decreases from 968.35 to 955.25 MPa, the arithmetic mean deviation increases by 1.4%, and when ultimate tensile stress increases to 961.18 MPa, the arithmetic mean deviation increases by 0.6%. When the cycle decreases from 262,142 to 137,433, the arithmetic mean deviation shows that less than a 90.74% increase in the cycle is obtained. For the three-dimensional printed dental implants, the higher the surface roughness, the lower the mechanical properties, ultimately leading to decreased implant life and poor performance.

Mathematical modeling of auxetic systems: bridging the gap between analytical models and observation

Abstract: 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

Development of calcium fluoride thin film on Ti-6Al-4V material by a dip coating process with an intermediate shellac layer for biocompatible orthopedic applications

Abstract: 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.

Microstructural and mechanical studies of feedstock material in continuous extrusion process

Abstract: The challenge encountered in continuous forming process is the variation in mechanical strength of product formed with respect to process variables like extrusion wheel speed and diameter of product. In this research article, the micro-structural investigation of the aluminum (AA1100) feedstock material of 9.5-mm diameter has been carried out at various extrusion wheel speeds and diameter of product before and after deformation on commercial continuous extrusion setup TBJ350. The mechanical properties like yield strength as well as percentage elongation have been estimated and optimized using two variables with 3 levels through central composite rotatable design (CCRD) method. The mathematical modeling has been carried out to predict the optimum combination of process parameters for obtaining maximum value of yield strength and percentage elongation. The statistical significance of mathematical model is verified through analysis of variance (ANOVA). The optimum value of yield strength is found to be 70.939 MPa at wheel velocity of 8.63 rpm and product diameter of 9 mm respectively, whereas the maximum percentage elongation recorded is 46.457 at wheel velocity of 7.06 rpm and product diameter of 7.18 mm. The outcome may be useful in obtaining the best parametric combination of wheel speed and extrusion ratio for best strength of the product.

Effect of cone angle of cylindrical pin in the SFSW and DFSW on mechanical properties of AA6061-T6 alloy

Abstract: 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.

Ductile failure analysis of epoxy resin plates containing multiple circular arc cracks by means of the equivalent material concept

Abstract: 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.

Numerical model development to predict the behaviour of infant/neonate crash dummy restrained inside of an incubator under deceleration

Abstract: In this paper, advanced finite element (FE) methods are developed to investigate the effect of deceleration on the crash dummy test complied with British Standard Engineering (BS EN 1789). These techniques, which are related to material modelling, joints and contacts, offer an advanced numerical model representing an infant incubator with all complex boundary conditions and design contents. It is shown that the response of an infant incubator is a function of the ratchet straps, the tension on the belts, the belt type and the distance of the belts from the edges of the incubator, which can significantly affect the experienced acceleration, by the infant. The validation process is performed against experimental studies and various case parameters such as crash dummy mass and negative acceleration impulse are discussed in detail. The developed numerical model is capable to predict the behaviour of the crash dummy and the incubator in terms of acceleration, trajectory and kinematics by less than 8% error.

Prediction of buckling force in hourglass-shaped specimens

Abstract: It is important to avoid buckling during low-cycle fatigue testing. The buckling load is dependent on the specimen shape, material properties, and the testing machine. In the present investigation of hourglass-shaped specimens the importance of the diameter to radius of curvature is examined. Diameters of 5 and 7 mm are examined with a ratio of radius of curvature to diameter of 4, 6, and 8. The machine used is an Instron 8800 with elongated rods for a climate chamber. This leads to a reduced stiffness of the machine during compression testing. A finite element model (in Abaqus) is developed to identify the critical buckling force. For hourglass-shaped specimens, buckling means onset of sideways movement, without a drop in the applied load which is typical for conventional Euler buckling. The onset of sideways movement is identified experimentally by analysis of the data from extensometer and the load cell. This model is verified by experiments and fits within 0.6 to − 11% depending on the specimen diameter and diameter to radius of curvature ratio. The smallest deviations are obtained for the 7-mm-diameter specimen with deviation varying from 0.6 to − 3.3% between the model and the experiments. The current investigation is done with a commercially available hot rolled structural steel bar of O16 mm.

Experimental investigations and empirical relationship on the influence of innovative hub geometry in a centrifugal fan for performance augmentation

Abstract: 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 75% for head coefficient and 77% 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