Aluminium metal matrix composites: A retrospective investigation

Aluminium matrix composites (AMMCs) are considered to be new generation potential materials for many engineering applications. Different kinds of reinforcement have been infused into the aluminium matrix in order to improve hardness, toughness, stiffness, wear resistance, fatigue properties, electrical properties and thermal stability as compared to their conventional unreinforced counterparts. The characteristics of AMMCs depend largely upon the type of reinforcement materials, interface bonding and processing parameters. In this article we have attempted to investigate the development of aluminium metal matrix composites (AMMCs) along with associated challenges and significant application areas

Tubercular myositis of infraspinatus: a rare clinical entity

Tuberculosis of the musculoskeletal system is generally confined to bones and joints. The surrounding soft tissue is secondarily infected. Tuberculous bursitis, tenosynovitis and primary pyomyositis are rarer manifestations of the disease. Of these, primary tuberculouspyomyositis is probably the rarest entity. We report a case of tubercular myositis of infraspinatus in an 8 year-old female who presented with pain, low grade fever, weight loss, anorexia, progressively increasing pain in the scapular region and restriction of movements. There was no history of trauma, diabetes, immunosuppression, corticosteroid usage, or renal failure. History of contact was present. Tenderness was present along the medial border of scapula and movements of upper extremity requiring movement of the scapula were painful and grossly restricted. MRI of the scapulothoracic region and shoulder revealed small amount of fluid along medial border of scapula with T2 hyperintensity of infraspinatus. Histopathology showed caseous necrosis, inflammatory cells and granulomatous cells suggestive of tuberculosis. Polymerase Chain Reaction for Mycobacterium tuberculosis was found to be positive. Patient was started on four-drug antitubercular treatment and regular dressings. The patient’s general condition improved and at 4 weeks post starting ATT, there was no pain and the patient was able to perform complete range of movement. This is probably the first reported case of tubercular myositis of infraspinatus in an immunocompetent patient without any identifiable focus elsewhere in the body. Rarity of the condition, presence of characteristic findings on MRI and histopathology make the case illustrative for young Orthopaedics surgeons.

Tribological characterization of eco-designed aluminium hybrid metal matrix composites

47-57In present experimental investigation, wear characteristics of Al 7075-T6/Eggshell/SiC/Al2O3 hybrid composites (Al 7075-T6 as base metal with eggshell particles wt. % 0.5, 1and 1.5, average particle size ~ 60 µm, SiC particles wt. % 1, 1.5 and 2, average particle size ~ 65 µm and Al2O3 particles wt. % 1.5, 2 and 2.5, average particle size ~90 µm) synthesized through electromagnetic stir casting route have been studied at various specimen temperatures under dry and lubricated test conditions. Wear investigations have been conducted on pin-on-disk rotary tribometer at a constant load of 20 N for a sliding speed of 2m/s and sliding distance of 2 km. Tribological attributes of synthesized composites have been evaluated as the function of reinforcements content and mechanical stirring time, as per the design of experiment according to Taguchi L9 orthogonal array. Experimental study has shown that at 30 ºC pin temperature under dry wear condition, among the developed hybrid composites, specimen S8 demonstrated a maximum relative decrease of 60% in wear loss while with lubrication the wear loss has been relatively decreased by 89% as compared to the base metal (specimen S0). At elevated pin temperature of 70 ºC under dry wear condition, the hybrid composite specimen S8 exhibited maximum relative reduction of 82% in wear loss whereas under lubricated condition the wear loss has been relatively reduced by 82% in comparison of their unreinforced counterpart (specimen S0). With exceedingly augmented tribological attributes, the current study strongly rationalizes high temperature wear resistant applications of synthesized aluminium hybrid composites with a total reinforcement weight percentage of 4.5% only (specimen S8).

Parametric optimization of fatigue behaviour of hybrid aluminium metal matrix composites

For various aerospace applications aluminium has emerged as most preferred material due to desirable attributes such as superior strength to density ratio, greater specific strength, better corrosion resistance, high toughness and cost effectiveness. The most desirable characteristics for aerospace materials are ability to withstand elevated temperature and sustain higher fatigue loadings. Current experimental investigation was carried out to explore and optimize fatigue characteristics of hybrid composites developed by infusing particulate reinforcements into aluminium alloy. Eggshell particles (wt% 0.5, 1 and 1.5, average particle size approximate to 60 mu m), Silicon Carbide particles (wt% 1, 1.5 and 2, average particle size approximate to 65 mu m) and Aluminium Oxide particles (wt% 1.5, 2 and 2.5, average particle size approximate to 90 mu m) were reinforced into Al 7075-T6 metal matrix through electromagnetic stir casting route as per L9 orthogonal array of Taguchi's approach in order to synthesize hybrid aluminium metal matrix composites with enhanced fatigue resistance. Analysis of variance (ANOVA) was also conducted to observe the effect of different process parameters on fatigue life of developed composites. Nine hybrid composite specimens and one as-cast Al7075-T6 specimen (in three replications) were prepared in accordance with ASTM E 468/606 and were evaluated for low cycle fatigue resistance at a constant load of 2 kg and constant speed of 500 rpms on rotating beam fatigue testing machine. It was observed that at 30 degrees C temperature, hybrid composite specimens exhibited significant enhancement in fatigue resistance in terms of reversible load cycles survived. The as-cast Al 7075-T6 specimen sustained only 94 load cycles while the highest number of load cycles i.e. 4560 were survived by hybrid composite specimen with Al 7075-T6 as base metal reinforced with 1.5 wt% of eggshell particles, 1.5 wt% of SiC particles and 1.5 wt% of Al2O3 particles (total reinforcement content only 4.5%) and mechanically stirred for 360 s

Minimum and Maximum Limit to Number of Myosin II Motors Participating in an Ensemble Motility

Extensive research on centrifugal compressors has been planned to define diffuser stall limits for a group of stages characterized by low blade-outlet-width-to-impeller-radius-ratio. Very little data is available on this centrifugal compressor family, especially for the last stage configuration. In addition, the most important stall diffuser prediction criteria barely cover this machine type. Many experimental tests have been planned to investigate several geometry variations. A simulated stage with a backward channel upstream, a 2D impeller with a vaneless diffuser and a constant cross section volute downstream constitute the basic geometry. Several diffuser geometries with different widths, pinch shapes, diffusion ratios were tested. Test results and conclusions are shown in the paper in terms of critical diffuser inlet flow angles, flow coefficients at stall inception and stage working ranges. The main task of the present work is to increase the knowledge and the amount of available data to characterize rotating stall phenomena, in particular for very narrow stages

Experimental investigation of ball bearing lubrication conditions by shock pulse method

Lubricant (grease) is a vital requirement of ball bearing system. Grease not only protects ball bearing from wear and tear but performs various other functions that are essential for proper functioning of ball bearings. The lubricant (grease) under different conditions attains different properties which in turn affect the performance of the ball bearings. The effect of the condition of the lubricants on the performance of the ball bearings is well documented. the work reports about the investigation of ball bearing using shock pulse method by using two different instruments (Tester T2000 Model and Shock Pulse Meter 43A) of different operating conditions of ball bearing the condition such as used the quantity of grease as different percentage (0%, 25%, 50%, 75%, 100%) and bad quality grease (burn grease) at different rpm at a fixed load (10kg) and compare the normalized shock pulse value (dB) at different operating conditions. This method uses a piezo-electric accelerometer superimposed electrically as well as mechanically to about 32 kHz of resonant frequency. The result will help in bearing related to quantity as well as quality condition based maintenance choosing the optimum conditions for detecting the lubricant problem in ball bearing

Fabrication of prototype connecting rod of PLA plastic material using FDM prototype technology

Rapid prototyping (RP) have been attracting attention in the manufacturing community because of their capability to reduce the lead time of product development. Present work is an effort to understand the influence of process variables like infill pattern, layer thickness, build orientation and infill density on dimensional accuracy (DA), flatness and cylindricity. Taguchi method orthogonal array L9 was used for the conduction of experiments. MakerBot Replicator-2 was used for the fabrication of scaled prototype connecting rod of polylactic acid (PLA) material. DA, flatness and cylindricity of the component were measured by using coordinate measuring machine (CMM). Analysis of variance (ANOVA) was employed to find out the significance of process parameters. A regression model was developed to predict the DA, flatness and cylindricity. The results reveal that the optimum process parameters for the DA, flatness and cylindricity were different. Utility Theory was used to find out the best process parameter condition. The best process parameters for the DA, flatness and cylindricity was found to be layer thickness 100 μm, linear infill pattern, inclined at 45ºorientation and 20% infill density. A confirmation test was conducted for checking the goodness of the model, which reveals that results were within the confidence limit

Fabrication of prototype connecting rod of PLA plastic material using FDM prototype technology

333-343Rapid prototyping (RP) have been attracting attention in the manufacturing community because of their capability to reduce the lead time of product development. Present work is an effort to understand the influence of process variables like infill pattern, layer thickness, build orientation and infill density on dimensional accuracy (DA), flatness and cylindricity. Taguchi method orthogonal array L9 was used for the conduction of experiments. MakerBot Replicator-2 was used for the fabrication of scaled prototype connecting rod of polylactic acid (PLA) material. DA, flatness and cylindricity of the component were measured by using coordinate measuring machine (CMM). Analysis of variance (ANOVA) was employed to find out the significance of process parameters. A regression model was developed to predict the DA, flatness and cylindricity. The results reveal that the optimum process parameters for the DA, flatness and cylindricity were different. Utility Theory was used to find out the best process parameter condition. The best process parameters for the DA, flatness and cylindricity was found to be layer thickness 100 µm, linear infill pattern, inclined at 45º orientation and 20% infill density. A confirmation test was conducted for checking the goodness of the model, which reveals that results were within the confidence limit

Effect of Thermal Strain, Induced by Cryogenic Cooling, on a High Homogeneity Superconducting Magnet for MRI Applications

The heart of the modern whole body MRI scanners is a superconducting magnet producing the required magnetic field with high homogeneity. The superconducting magnet operates at 4.2 K (-268.95 oC) and thus is kept dipped in liquid helium to maintain its superconducting state. This cooldown of the multi-coil magnet from room temperature to the LHe temperature generates thermal strains in the magnet structure which deforms the magnet. These deformations are found to affect the final magnetic field homogeneity and introduce artifacts in the MR images. We report our results on studies on the stresses induced in the bobbin and the coils consequent upon cooling the magnet to 4.2 K. The maximum von Mises stress in the coils is calculated to be 31.3 MPa while in the bobbin it comes out to be 60 MPa. We find that the cooldown causes a relative movement of the coils which in turn degrades the field homogeneity from 5.5 ppm to 278 ppm. The centre field is found to increase by 60 G is caused by a reduction in the overall cross-section of the coils. The change in homogeneity is also analysed in terms of Legendre polynomials where we found that the relative displacements of the coils introduce odd order terms to the polynomial expansion terms which were not present in the original design

Microstructure and Wear Study of Al 7075-T6/Eggshell/SiC/Al2O3 Hybrid Composites

In present experimental investigation, hybrid aluminium metal matrix composites were fabricated using stir casting technique by infusing eggshell particles (0.5, 1 wt%), SiC particles (1, 1.5 wt%) and Al2O3 particles (1.5, 2.5 wt%) into Al 7075-T6 metal matrix. The developed composites were further characterized for microstructures using FESEM, X-ray diffractometry and EDS techniques. Tribological behaviour investigations were carried out using a pin-on-disk tribometer for comparative study between as-cast Al 7075-T6 alloy and Al-7075-T6/Eggshell/SiC/Al2O3 composites. During dry sliding wear test at room temperature, there was a decrease of 33% in wear rate, 20% in coefficient of friction and 20% in frictional force of composites, whereas in presence of lubricant, the developed composites exhibited maximum reduction of 85% in wear rate, 46% in coefficient of friction and 46% in frictional force as compared to their unreinforced counterparts. Due to augmented tribological properties, fabricated hybrid composites can reasonably be used for lightweight wear-resistant applications