Scielo RSS <![CDATA[R&D Journal]]> http://www.scielo.org.za/rss.php?pid=2309-898820190001&lang=en vol. 35 num. lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Peridynamic Approach to Predict Ductile and Mixed-Mode Failure</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2309-89882019000100001&lng=en&nrm=iso&tlng=en The peridynamic theory has been developed to address problems in solid mechanics regarding fracture through its integral non-local basis. It has been successful in predicting brittle cracking, however, uncertainty still remains with regards to mixed mode and ductile fracture. This work presents a study in using peridynamics to simulate fracture in mixed mode or ductile type fractures. The results are presented as a quantitative comparison between experimental tests and numerical simulations. Standard compact tension tests were performed on polymethyl methacrylate (PMMA), stainless steel 304L and aluminium 1200H4 to obtain the respective JR-curves and critical energy release rates, Jic. In addition, digital image correlation was employed to allow for qualitative observation of the fracture process and choice in peridynamic input parameters. An equivalent critical stretch was determined for each material and applied to an Arcan geometry. It is shown that the energy release rate for mode I and mode II should be considered separately. Mixed mode type failures cannot be simulated accurately by a single critical stretch criterion. Furthermore, ductile fracture requires careful consideration when selecting peridynamic input parameters. <![CDATA[<b>Statistical Analysis of Effects on Weld Response Variables during Friction Hydro-Pillar Processing</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2309-89882019000100002&lng=en&nrm=iso&tlng=en The article provides insight to the complex relationships that exist between the selected weld process parameters and the associated effects on weld responses by application of statistical analysis relating to response predictive models for Friction Hydro-Pillar Processing (FHPP). The literature review focused at obtaining the current assumptions made with regards to the relationship between FHPP and conventional Friction Welding (FW) variations. Experimental welds were produced at varying selected process parameters; motor speed, axial force, consumed length and forging time. These parameters were compared to five weld response variables through a 27-run full factorial Design of Experiment and multiple regressions. The analysis focussed on quantifying the main effects of process parameters on energy input, temperature profile, friction time, torque and consumed rate. Comparison with experimental results served to validate the effect of dominant process parameters. The process and statistical analysis are explained in detail to assist further understanding of the applied methodology and the effect of the various process parameters on weld responses presented. Results indicate that the mathematical equation based models predict the responses adequately within the limits of welding parameters used and that no single parameter solely control the weld responses during FHPP. This study provides a clearer understanding of FHPP showing that generalised conclusions, with regards to the influences of process parameters on weld responses during conventional FW, cannot be made as the effects of these inputs differ depending on the combination of levels included in a parameter set. <![CDATA[<b>Bagasse-Based Desiccant Wheel Dehumidifier</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2309-89882019000100003&lng=en&nrm=iso&tlng=en Green desiccants are obtainedfrom natural waste products like bagasse. They are fully biodegradable and cause no harm to the environment compared to chemical desiccants. A bagasse-based desiccant wheel dehumidifier that uses a green desiccant like sugarcane bagasse to remove humidity from air has been implemented and tested. Sugarcane bagasse was chosen as the main desiccant since it not only shows high adsorption properties but is also abundant in Mauritius and is much cheaper compared to other desiccants. The prototype was implemented and tested under various input parameters. A mathematical model was constructed to show how the dehumidification rate varies with airflow, desiccant wheel speed and bagasse thickness. It was found that dehumidification rate increases with an increase of the previously mentioned parameters. Another finding showed that as dehumidification rate increases, a higher regeneration rate for the desiccant is required. At maximum operating conditions, the dehum idifier has a Coefficient of Performance of 0.0118 and a Moisture Removal Capacity of 2.06 g/min. It could also be deduced that at lower temperature, the prototype has a better efficiency. A controller was implemented and incorporated in the dehumidifier which responded well to different inlet air relative humidity and temperature. <![CDATA[<b>A computational study on additively manufactured welding electrodes</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2309-89882019000100004&lng=en&nrm=iso&tlng=en Advances in additive manufacturing technology present new design opportunities for metal parts that would otherwise be infeasible with subtractive manufacturing technologies. Clifford Machines & Technology (Pty) Ltd is an international producer of large mesh welding machines. The research was conducted with the aim of investigating the advantages that can be provided through the redesign of the mesh welding electrodes, for production using additive manufacturing. Simulation studies were applied in order to evaluate the performance of the redesigned electrodes and the results were compared to the existing electrodes. The results show that the electrodes designed for additive manufacturing achieved mass reductions of up to 58.2%. The electrodes were also able to support increases of current density by up to 98%, while operating at a lower temperature than the original electrodes. The study has identified the high initial cost of production and increased power consumption to be the disadvantages of additively manufactured electrodes. <![CDATA[<b>A parametric design and optimization approach to enhance the fatigue life of a male pyramid socket adapter</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2309-89882019000100005&lng=en&nrm=iso&tlng=en This research paper presents a parametric design approach to optimize a male pyramid socket adapter as used on a transtibial prosthetic limb for enhanced fatigue life. These adapters are prone to premature failure when used by individuals partaking in athletic sports. A parametric design and optimization approach is presented and applied. A current design was assessed for structural integrity by finite element analysis in combination with the load criteria as recommended by the ISO 10328:2016 code of practice. Highly-stressed regions where identified and improved using a parametric design approach to reduce the maximum 1st Principal stress while adhering to the industry code of practice as applicable to pyramid socket adapter design. The optimization was validated by experimentally comparing the current design and the optimised design for an appropriate load case by low cycle fatigue testing. The socket adapters were manufactured from Ti6Al4V and subjected to a simulated resultant knee bending moment. The fatigue validation indicated a significant improvement in fatigue life for the optimized socket geometry commensurate with a reduction in stress and comparison to an appropriate SN curve for Ti6Al4V. The parametric optimization process as utilized was found to be effective and should be applicable to many different applications in a more general sense. <![CDATA[<b>Slip Factor Prediction for Impellers with Straight, Back-swept Blades</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2309-89882019000100006&lng=en&nrm=iso&tlng=en Slip factor accounts for the deviation of the flow angle from the trailing edge blade angle at the exit of radial impellers. Accurate values are required to predict impeller torque and energy input. The slip factor prediction method for back-swept radial bladed impellers is based on the so-called single relative eddy (SRE) method, which is an approximation of the classical, two-dimensional analytical solution to the inviscid flow problem. The relatively accurate prediction of the slip factors of 19 impellers found in four data sets published since its formulation, shows the reliability of the SRE method. The characteristics of straight-bladed impeller layouts are explored and incorporated into the SRE method. It turns out that the SRE method as developed for logarithmic spiral blades predicts the inviscid flow slip factor of 42 different straight bladed impeller geometries accurately, when a correction for the critical radius ratio at low blade numbers is introduced. Predicted slip factor values are also compared to new experimental data for five different impellers with straight, back-swept blades, over a range of three blade angles and three blade numbers. Agreement is excellent near the flow coefficient corresponding to the volute design angle.