COMPUTATIONAL MODELING OF THE FRICTION STIR WELDING (FSW) PROCESS AND OF THE PERFORMANCE OF FSW JOINTS

Friction Stir Welding (FSW) is a solid-state metal-joining process. Within FSW, a (typically) cylindrical tool-pin (threaded at the bottom and terminated with a circular-plate shape shoulder, at the top) is driven between two firmly-clamped plates (placed on a rigid backing support). Due to a high normal downward pressure applied to the shoulder and due to frictional sliding and plastic-deformation, substantial amount of heat is generated at the tool/work-piece interface and in the region underneath the tool shoulder. Thermally plasticized work-piece material is then extruded around the traveling tool and forged into a welding-joint behind the tool. Due to its solid-state character and lower process temperatures, FSW possesses a number of advantages in comparison to the conventional fusion welding processes. In the present work, advanced computational methods and tools are used to investigate three specific aspects of the FSW process: (a) material flow and stirring/mixing: Within the numerical model of the FSW process, the FSW tool is treated as a Lagrangian component while the workpiece material is treated as a Eulerian component. The employed coupled Eulerian/Lagrangian computational analysis of the welding process was of a two-way thermo-mechanical character (i.e. frictional-sliding/plastic-work dissipation is taken to act as a heat source in the thermal-energy balance equation) while temperature is allowed to affect mechanical aspects of the model through temperature-dependent material properties. The workpiece material (AA5059, solid-solution strengthened and strain-hardened aluminum alloy) is represented using a modified version of the classical Johnson-Cook model (within which the strain-hardening term is augmented in order to take into account for the effect of dynamic recrystallization) while the FSW tool material (AISI H13 tool steel) is modeled as an isotropic linear-elastic material. Within the analysis, the effects of some of the FSW key process parameters are investigated (e.g. weld pitch, tool tilt-angle and the tool pin-size). The results pertaining to the material flow during FSW are compared with their experimental counterparts. It is found that, for the most part, experimentally observed material-flow characteristics are reproduced within the current FSW-process model; (b) modifications of the existing workpiece material models for use in FSW simulations: Johnson-Cook strength material model is frequently used in finite element analyses of various manufacturing processes involving plastic deformation of metallic materials. The main attraction to this model arises from its mathematical simplicity and its ability to capture the first order metal-working effects (e.g. those associated with the influence of the extent of plastic deformation, rate of deformation and the attendant temperature). However, this model displays serious shortcomings when used in the engineering analyses of various hot-working processes (i.e. those utilizing temperatures higher than the material recrystallization temperature). These shortcomings are related to the fact that microstructural changes involving: (i) irreversible decrease in the dislocation density due to the operation of annealing/recrystallization processes; (ii) increase in grain size due to high-temperature exposure; and (iii) dynamic recrystallization-induced grain refinement, are not accounted for by the model. In the present work, an attempt is made to combine the basic physical-metallurgy principles with the associated kinetics relations in order to properly modify the Johnson-Cook material model, so that the model can be used in the analyses of metal hot-working and joining processes. The model is next used to help establish relationships between process parameters, material microstructure and properties in FSW welds of AA5083 (a non-age-hardenable, solid-solution strengthened, strain-hardened/stabilized Al-Mg-Mn alloy); and (c) FSW-joint failure mechanisms under ballistic impact loading conditions: A critical assessment is carried out of the microstructural changes, of the associated reductions in material mechanical properties and of the attendant ballistic-impact failure mechanisms in prototypical Friction Stir Welding (FSW) joints found in armor structures made of high-performance aluminum alloys (including solution-strengthened and age-hardenable aluminum alloy grades). It is argued that due to the large width of FSW joints found in thick aluminum-armor weldments, the overall ballistic performance of the armor is controlled by the ballistic limits of its weld zones (e.g. heat affected zone, the thermo-mechanically affected zone, the nugget, etc.). Thus, in order to assess the overall ballistic survivability of an armor weldment, one must predict/identify welding-induced changes in the material microstructure and properties and the operative failure mechanisms in different regions of the weld. Towards that end, a procedure is proposed in the present work which combines the results of the FSW process modeling, basic physical-metallurgy principles concerning microstructure/property relations and the fracture mechanics concepts related to the key blast/ballistic-impact failure modes. The utility of this procedure is demonstrated using the case of a solid-solution strengthened and cold-worked aluminum alloy armor FSW-weld test structure

Changing Contexts of Customer Service in the Social Media Era: Challenges and Opportunities for Indian e-tail Industry

The research aims to analyse the impact of social media on customer service provided by the E-tailing companies in India. The analysis depicted that antecedent variables of customer service such as personal greetings, idea generation, loyalty benefits, and feedback mechanisms have a positive impact but they fail to create an impression on the consequence variables such as loyalty development, time efficiency, and knowledge creation. Researchers conclude that the lack of clarity in media vehicles communication, proliferation of e-tailing, and their rivalry create issues among the consumers of E-tail companies

Ensuring Audible Confirmations for Digital Payments via Speaker Devices

Quick response (QR) codes are a popular way to initiate payment to a merchant via a digital payment app. Many merchants utilize speaker devices connected to a payment service to automatically receive audible confirmation of received payments. Merchants that display multiple QR codes may only have a subset of the codes linked to a speaker device. This disclosure describes the use of augmented reality techniques to automatically indicate the availability of a speaker device for a particular QR code such that customers can initiate payment with confidence that an audible confirmation will be delivered via an in-store speaker. Further, payment via QR codes can fail if the QR code is unreadable. This disclosure describes techniques to automatically detect merchant identity based on faded or otherwise unreadable QR codes and/or on merchant location and to display a valid QR code atop the camera field of view. The customer can perform a sound check to confirm the merchant identity and then initiate payment, allowing the merchant to receive payment even when the QR code is unreadable

A Point-of-Sale Digital Payment Device for Extending Credit

In the absence of credit scores, credit penetration remains low in many regions of the world. This limits economic opportunities for a large portion of the global population that lack credit histories. For many users, traditional sources of credit such as banks or microfinance institutions are difficult to access and cumbersome and are not tailored to their financial needs. This disclosure describes a compact, internet-connected payment device that can be deployed at small and medium-sized business (SMB) outlets. The device serves both as a digital payment terminal as well as an access point for credit discovery and lending. With appropriate permissions, the device can leverage SMB sales data to assess the creditworthiness of regular customers. Customers can access credit offers via a simple user interface and make repayments via familiar digital payment mechanisms

Maternal Satisfaction Through Breastfeeding: An empirical study

A growing body of research indicates that both mothers and children benefit from breastfeeding. Reflecting such research, public health officials and organizations promote the practice of breastfeeding. Despite such research, advocacy, and gradually increasing breastfeeding rates over the past decade, a large fraction of mothers do not breastfeed for a shorter period than the recommended six months. We have identified maternal satisfaction (MS) as a predictor variable and six criterion variables namely maternal knowledge (MK), a socio-cultural attitude of mothers (SCI), mother-baby bonding (MBB), family tradition (FT), concerns for health and figure (CHF), and government initiatives (GI). Primary data were collected from hospitals, tabulated and processed to draw the inferences and relationships among the variables. Results show that there is weak maternal knowledge among the mothers, especially for the first baby delivery. Moreover, there are many concerns like family traditions, social and cultural attitudes, mothers concerns on health and physical figure, government initiatives with maternal satisfaction in our study. Keywords: Maternal satisfaction, breastfeeding DOI: 10.7176/JHMN/95-08 Publication date: November 30th 202