Balkrishna C. Rao

This paper discusses tensile testing of small samples of nanocrystalline Al6061-T6 alloy obtained from an unusual application of machining as a severe plastic deformation process. Ultrafine grained (UFG) shavings obtained from plane-strain cutting show higher hardness than the bulk material in agreement with existing literature. Application of restricted contact tools and extrusion-machining was explored to obtain shavings with minimum curvature to aid in tensile test specimen preparation. A novel method to prepare small tensile test specimens from these shavings has been described. During the tensile testing of UFG material, strains were measured using digital image correlation of natural speckles on the specimen. Specimens made from the UFG material had higher tensile strength and yield stress than the bulk, while ductility was lower. Lower values of Young's modulus were observed during the tensile testing of small specimens made from UFG as well as bulk material. © Materials Research Society 2014.

This work is focused on the development of a dual-layered diamond-coated tungsten carbide tool for machining titanium Ti-6Al-4V alloy. A hot-filament chemical vapor deposition technique was used to synthesize diamond films on tungsten carbide tools. A boron-doped diamond interlayer was added to a microcrystalline diamond layer in an attempt to improve the interface adhesion strength. The dual-layered diamond-coated tool was employed in machining at cutting speeds in the range of 70 to 150 m min-1 with a lower feed and a lower depth of cut of 0.5 mm rev-1 and 0.5 mm, respectively, to operate in the transition from adhesion- to diffusion-tool-wear and thereby arrive at suitable conditions for enhancing tool life. The proposed tool was then compared, on the basis of performance under real-time cutting conditions, with commercially available microcrystalline diamond, nanocrystalline diamond, titanium nitride and uncoated tungsten carbide tools. The life and surface finish of the proposed dual-layered tool and uncoated tungsten carbide were also investigated in interrupted cutting such as milling. The results of this study show a significant improvement in tool life and finish of Ti-6Al-4V parts machined with the dual-layered diamond-coated tool when compared with its uncoated counterpart. These results pave the way for the use of a low-cost tool, with respect to, polycrystalline diamond for enhancing both tool life and machining productivity in critical sectors fabricating parts out of titanium Ti-6Al-4V alloy. The application of this coating technology can also be extended to the machining of non-ferrous alloys owing to its better adhesion strength.

Frugal products possess a proper mix of features including minimal consumption of resources, good functionality under nominal conditions and low cost. Therefore, increasing use of frugal products, that are designed and also fabricated systematically, is crucial to all-round sustainable development. However, their low factor-of-safety rigorous-design makes them inherently prone to failure under conditions of overloading. And multitudes of such coupled-products would create topologies of interconnected complex systems in the foreseeable future whose individual products should be made to adapt against any events of failure to enhance functionality while maintaining low cost. Accordingly, this paper proposes a two-pronged methodology for adaptation of frugal products along with ramifications of complex systems of frugal products. The adaptation methodology is crucial to the functioning of individual and also networks of frugal products and this work accordingly explicates scenarios of ensuing networks. Other than application to various sectors including electric vehicles, a basic example of which is covered in this paper, the proposed adaptation-and-networking framework can also be applied to a growing numbers of sustainable products, which are frugal according to the terminology of this effort and hence prone to premature failure.

Manufacturing is a crucial activity of product development that feeds into and is also influenced by the design process. Any material conservation gained during manufacturing directly affects the green credentials of a product. Manufacturing waste can be contrived to approach zero through a recently developed frugal design approach that quantifies resource conservation at all stages of development of a product engineered for frugality. Accordingly, this effort presents frugal manufacturing (FM), integral to the frugal design approach, for utmost reduction of waste while aiming for good surface integrity, better properties, minimal number of processes and low cost. Other than saving on energy and hence emissions, the new concept of FM also goes beyond current near net shape technologies, which advocate mainly for zero wastage and suitable properties while using a narrow range of manufacturing processes. Case studies involving high-speed machining, superplastic forming and additive manufacturing of aerospace alloys have been presented that bring out the features and benefits of FM. As such the multipronged objectives of FM should be dovetailed with those of smart factories for creating novel technologies that abet widespread sustainable development. Such enhancement of the smart factories concept has been argued to support unusual applications such as the fight against pandemics including the current one involving COVID-19.

In the present effort, impact of bullets fired at high speeds on a stationary target was used as a high strain-rate plastic deformation method to generate Functionally Graded Materials (FGMs). The bullet-shaped Aluminum alloy Al5052 specimens impacted the UHMWPE target at different projectile velocities ranging from 100 m/s to 750 m/s, to study the effect of the impact speed. Moreover, few of the projectiles impacted along the longitudinal axis whereas the remaining projectiles impacted with an obliquity to investigate the effect of leading-edge shape. The metallography of the projectile specimens fired at 750 m/s shows grain refinement from 70 ± 3 μm at the rear/ un-deformed point to 10 ± 1 μm at the front/ severely deformed point which is in the impact zone. Similar but of less magnitude variations were observed at other impact speeds also. The hardness variation was 45% (70 ± 3 HV at the rear surface to 102 ± 2 HV at the front face) at 750 m/s. Moreover, least variation in hardness and grain size was observed for projectile impacted at lowest velocity tested (100 m/s). Further, functionality in hardness and grain refinement was seen in graded direction due to shape of the projectile specimens, impact velocity, and target material. Depending upon the impact angles, axisymmetric (impacted normal to the longitudinal axis) or unsymmetrical (impacted at an angle) variation of grain refinement and hardness was observed.

Tensile properties of metals are typically measured using dog-bone shaped specimens having dimensions as per specifications imposed by international standards organizations. However, these properties may be influenced by the size of the specimen, especially when the cross-sectional dimensions are lower. At lower length scales, microstructure could have an effect on the mechanical behavior. In this study, tensile experiments were conducted to investigate the effect of cross-sectional dimensions on Young’s modulus of Al6061-T6 materials. Due to the small size of the specimens, digital image correlation, a non-contact measurement technique was used to obtain strain filed in the gage section of the specimen. Spray paint or toner powder were used to produce speckle pattern on the specimen surface for better correlation of the images. For specimens having the thickness of the order of a fraction of a mm, the natural gray pattern observed on the surface of the specimen was found to provide a good speckle pattern. This natural speckle pattern was used to correlate the images instead of synthetic speckles, to avoid the effect of paint on the Young’s modulus being measured on specimens with cross-sectional dimensions below 1 mm. Young’s modulus was found to be constant at about 67 GPa for specimens whose area of cross-section was more than 3 mm2. When the area of cross-section was lesser, Young’s modulus was found to decrease with a decrease in area of cross-section. Larger spread in Young’s modulus was also observed in the specimens with area of cross-section < 1 mm2.

The characterization of Ni-based superalloy Inconel® 718 fabricated by powder-based laser fusion process was performed to study microstructural evolution and accompanying mechanical properties of as-deposited and post-heat-treated material. The current effort employs a low laser volumetric energy density during the deposition. X-ray diffraction, optical, and scanning electron microscopy were done for microstructural characterization. Examination of hardness values, tensile properties, and fractography based on sample orientation was also performed. X-ray diffraction studies facilitated qualitative confirmation of as-deposited samples possessing cube texture. The optical and scanning electron micrographs aided in examining the evolution of microscopic features after each post-processing stage. The as-deposited material possessed columnar grain morphology along with melt-pool marks, which on further magnification showed cellular-dendritic sub-grains along with Laves phases in the interdendritic grain boundaries. Solution heat treatment resulted in reducing these detrimental Laves phases and relief of thermal residual stresses caused by non-homogeneous recrystallization. Solution treatment also led to the formation of equiaxed grain clusters at various sample locations along with the existing columnar grains. The incoherent δ phase was formed at the grain boundaries along with coherent γ″ precipitates. The mechanical properties of as-deposited Inconel 718 alloy were near-isotropic in specimens oriented parallel and perpendicular to the build direction which is ascribed to low laser volumetric energy density. Micrographs of fractured surfaces taken for both directions of all sample conditions showed a ductile mode of fracture.

Sustainable development necessitates the management of progress in science and technology for society's betterment while preserving Earth's resources. In this regard, the appearance in recent years of low-cost sophisticated products consuming resources economically is a force for good. This effort terms each of these products as an advanced frugal innovation to highlight the frugality in resource consumption during the realization of these innovations through advances in various scientific disciplines. Other than 25 examples of advanced frugal innovations in a wide range of sectors from rural electrification to particle physics, a framework for the systematic realization of such innovations for sustainable development has also been described. The innovations showcased bring out the use of advances in science and technology or cutting edge knowledge for creating these low-cost sophisticated products. Moreover, the need for innovators typically with training in advanced knowledge areas to handle the sophistication in technology for the successful fruition of these innovations is also discussed. This effort supports the frugal design and frugal engineering of innovations, whether grassroots or the advanced type, through sound scientific principles for the creation of robust products, especially where the human life is at stake, in various sectors for all-round sustainable development.

The conservative nature of design in engineering has typically unleashed products fabricated with generous amounts of raw materials. This is epitomized by the factor of safety whose values higher than unity suggests various uncertainties of design that are tackled through material padding. This effort proposes a new factor of safety called the factor of frugality that could be used in ecodesign and which addresses both rigors of the classical design process and quantification of savings in materials going into a product. An example of frugal shaft design together with some other cases has been presented to explain the working of the factor of frugality. Adoption of the frugality factor would entail a change in design philosophy whereby designers would constantly make avail of a rigorous design process coupled with material-saving schemes for realizing products that are benign to the environment. Such a change in the foundations of design would abet the stewardship of earth in avoiding planetary boundaries since engineering influences a significant proportion of human endeavors.

The morphology of fine microstructure arising from reversible martensitic transformations is known to depend on the sample size and orientation to applied thermal or mechanical loading. In this paper we study these effects using a novel discrete particle approach. Our new approach uses a multibody interparticle interaction for the discrete particles which is obtained directly from a polyconvex continuum free energy appropriate for such materials. In order to study the interfaces between the austenite and martensite phases, the material is subjected to a temperature gradient. A competition between self-accommodation which causes formation of twinned martensite and the requirement of compatibility of the phases on the interfaces results in very distinctive microstructures. We study the effect of the angle between the applied temperature gradient and the orientation of the parent phase on the phase boundary. In smaller samples, a phase boundary between austenite and a single variant of martensite forms due to the effect of the free surface and the resultant microstructure takes a banded form. Detwinning under applied mechanical loading is strongly dependent on the initial microstructure. The implicit kinetic relation for twin boundary propagation of this approach shows a classical stick-slip form.