Rheological characterization of styrene-butadiene based medium and its finishing performance using rotational abrasive flow finishing process

Finishing of complex shaped components needs advanced finishing processes to produce nano level surface finish. Abrasive flow finishing (AFF) process uses abrasive mixed polymer as a medium to finish complex shapes. The medium should possess three basic properties i.e., better flow ability, self deformability and abrading ability to finish the given surface to nano scale. Various flow and deformation properties of the medium can be investigated by rheological characterization. In the present work, different media are made using specially co-polymered soft styrene butadiene based polymer, plasticizer and abrasives. Static and dynamic rheological properties of these in-house prepared media are evaluated, and it is found that these media follow viscoelastic behavior with shear thinning nature. For a small rise in temperature, the medium starts losing its original properties.In the present work, static (flow test, creep compliance test, stress relaxation test) and dynamic (amplitude sweep and frequency sweep) rheological properties are measured. Finishing experiments are carried out on Al alloy as well as its metal matrix composites using rotational abrasive flow finishing (R-AFF) process. Later, the effect of each rheological parameter such as shear stress, % viscous component, stress relaxation modulus and storage modulus on the change in average surface roughness (ΔR_a) and material removal rate during R-AFF is found.     

Anchored block-copolymer surfactants for the synthesis of redispersible polystyrene latexes

Redispersible polystyrene (PS) latexes of particle sizes in the range of 200–220 nm was prepared using low-molecular-weight amphiphilic block copolymer surfactants. Latex powders were obtained by sun drying of the prepared PS latexes and were reintroduced into the solution by simple mechanical agitation/stirring without any additives. DLS and SEM analysis were carried out for pristine/sun-dried latexes to compare the size and shape of the particles. A series of block copolymers with 2-methyl-2-oxazoline and 2-butyl-2-oxazoline or 2-phenyl-2-oxazoline with repeat units 30/20, 60/20, 15/30, and 15/45 were synthesized through cationic ring opening polymerization (CROP) and were used as nonionic surfactants (NIS) in the preparation of poly(styrene) latexes by emulsion polymerization. In this work, we investigated the role of anchoring ability of butyl/phenyl groups of the block copolymer in providing stability and redispersibility of the latex by comparing with simply cetyl and stearyl surfactants that are devoid of such functionality. The ready redispersibility and retainment of size and shape as that of original latexes confirmed the role of anchoring groups. PS latexes prepared by block-copolymer surfactants that are devoid of anchoring units showed lesser stability and no redispersibility compared to anchored surfactants. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48875.     

An efficient key predistribution scheme for ad hoc network security

We introduce hashed random preloaded subsets (HARPS), a highly scalable key predistribution (KPD) scheme employing only symmetric cryptographic primitives. HARPS is ideally suited for resource constrained nodes that need to operate for extended periods without active involvement of a trusted authority (TA), as is usually the case for nodes forming ad hoc networks (AHNs). HARPS, a probabilistic KPD scheme, is a generalization of two other probabilistic KPDs. The first, random preloaded subsets (RPSs), is based on random intersection of keys preloaded in nodes. The second, proposed by Leighton and Micali (LM) is a scheme employing repeated applications of a cryptographic hash function. We investigate many desired properties of HARPS like scalability, computational and storage efficiency, flexibility in deployment modes, renewability, ease of extension to multicast scenarios, ability to cater for broadcast authentication, broadcast encryption, etc., to support its candidacy as an enabler for ad hoc network security. We analyze and compare the performance of the three schemes and show that HARPS has significant advantages over other KPDs, and in particular, over RPS and LM.     

A comprehensive dynamic cutting force model for chatter prediction in turning

This paper presents a model of the dynamic cutting force process for the three-dimensional or oblique turning operation. To obtain dynamic force predictions, the mechanistic force model is linked to a tool–workpiece vibration model. Particular attention was paid to the inclusion of the cross-coupling between radial and axial vibrations in the force model. The inclusion of this cross-coupling facilitates prediction of the unstable–stable chatter phenomenon which usually occurs in certain cases of finish turning due to process non-linearity. The dynamic force model developed was incorporated into a computer program to obtain time-saving chatter predictions. Experimental tests were performed on AISI 4140 steel workpieces to justify the chatter predictions of the dynamic cutting process model in both the finishing and roughing regimes. Experimental results corroborate the unstable–stable chatter predictions of the model for different cases of finish machining. In addition, experimental results also confirmed the accuracy of chatter predictions for various cases of rough turning.     

The effect of process parameters on machining of magnesium nano alumina composites through EDM

The effects of electrical discharge machining (EDM) parameters on drilled-hole quality such as taper and surface finish are evaluated. Microwave-sintered magnesium nano composites (reinforced with 0.8 and 1.2 wt.% of nano alumina) are used as work materials. Experiments were conducted using Taguchi methodology to ascertain the effects of EDM process parameter. The process parameters such as pulse-on time, pulse-off time, voltage gap, and servo speed were optimized to get better surface finish and reduced taper. ANOVA analyses were carried out to identify the significant factors that affect the hole accuracy and the surface roughness. Confirmation tests were performed on the predicted optimum process parameters. Pulse-on time and the servo speed are identified as major response variables. Micro structural changes and the effects of nano particle reinforcement in the drilled hole were studied through SEM micrographs.     

A technical note on ‘Analysis of closed loop supply chain using genetic algorithm and particle swarm optimisation’

This study analyses the mixed-integer linear program (MILP) proposed by Kannan et al. [Kannan, G., Noorul Hag, A., and Devika, M., 2009. Analysis of closed loop supply chain using genetic algorithm and particle swarm optimization. International Journal of Production Research, 47 (5), 1175–1200] in their paper entitled ‘Analysis of closed loop supply chain using genetic algorithm and particle swarm optimisation’. Since we find inconsistencies in the model, we propose modifications to rectify the flaws. The revised model is presented and tested using a hypothetical problem.     

Optimization of operating parameters and performance evaluation of forced draft cooling tower using response surface methodology (RSM) and artificial neural network (ANN)

Optimization of cold water temperature in forced draft cooling tower with various operating parameters has been considered in the present work. In this study, response surface method (RSM) and an artificial neural network (ANN) were developed to predict cold water temperature in forced draft cooling tower. In the development of predictive models, water flow, air flow, water temperature and packing height were considered as model variables. For this propose, an experiment based on statistical five-level four factorial design of experiments method was carried out in the forced draft cooling tower. Based on statistical analysis, packing height, air flow and water flow were high significant effects on cold water temperature, with very low probability values (< 0.0001). The optimum operating parameters were predicted using RSM, ANN model and confirmed through experiments. The result demonstrated that minimum cold water temperature was optioned from the ANN model compared with RSM.     

Investigation of Cracks Generated in Columbium Alloy (C-103) Sheets During Deep Drawing Operation

Columbium (Niobium) alloy C-103 sheets were formed through deep drawing operations. Two sheets out of a lot of six failed (cracked) during deep drawing. A detailed technical review and microstructural analysis of the failed component was carried out to find out the reasons for cracking. Visual observation of the failed component revealed localized thinning (cup-cone type) at the crack locations. Fractographic observations revealed a predominantly ductile mode of failure. The detailed analysis carried out indicated the failure (crack) is due to nonuniform deformation during first stage deep drawing. This paper provides detail of the failure analysis methodology and present reasons for the failure.     

Flow stress modeling for copper under changing process conditions

Realistic simulation of metal forming processes requires constitutive equations that describe the behavior of a material under varying process conditions. The equations that have hitherto been developed to address this problem are generally too involved and require the determination of many constants. In this paper, a simple approach based on the representative nature of the work hardening rate, which enables the use of an elementary rate equation in such modelling, is introduced. A prediction methodology based on the concept of fading memory is developed and is found to give good predictions in the case of copper. A mechanistic interpretation of the approach is proposed.     

Unusual structural stability and ligand induced alterations in oligomerization of a galectin

OBJECTIVE: To evaluate the balloon-occluded arterial infusion (BOAI) of cisplatin and adriamycin as a preoperative adjuvant chemotherapy in patients with bladder cancer of stage > or = T2 or in those with stage T1 and multiple large tumours. PATIENTS AND METHODS: The study comprised 120 patients with bladder cancer who underwent BOAI from November 1984 to December 1995. BOAI chemotherapy (adriamycin and cisplatin) was administered under ischaemia through a 7 F torque-control balloon catheter, both sides of which were inserted into the contralateral internal iliac artery. The regression rate of tumours and any improvement in tumour stage was assessed. RESULTS: The clinical response rate (complete or partial) was 66% and the tumour stage improved in 39% of the patients after BOAI. Of 26 patients with stage T3 a diagnosed before BOAI, 12 were diagnosed as T2 or less after treatment. Of 27 patients who underwent total cystectomy because the tumour was diagnosed as T2 after BOAI, the post-operative histopathological examination showed that 22 (82%) were stage pT1 or below. The features associated with a good response to BOAI in patients with up to pT3a disease were grade 3, non-papillary tumours with a diameter of < 3 cm. CONCLUSION: In patients diagnosed as stage T2 and T3a, or stage T1 with multiple large tumours difficult to be treat by transurethral resection, BOAI should be considered as the first choice to decrease the stage or to confirm the pathological staging.