Research Articles (Mechanical and Mechatronic Engineering)

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    Influence of powder characteristics on the spreadability of pre-alloyed tungsten-carbide cobalt
    (Southern African Institute for Industrial Engineering, 2021) Govender, Preyin; Blaine, Deborah Clare; Sacks, Natasha
    With rising interest in additive manufacturing (AM) techniques, there is an increased focus on research that evaluates critical parameters that guide the selection of powders that are suitable for AM. One such parameter is a powder’s spreadability, described by metrics such as powder bed density and percentage coverage. This study focused on three spray-dried WC-Co powders (two 12 wt% and one 17 wt% Co) and evaluated the influence of typical powder characteristics, such as particle size and shape, apparent density, and flow rate, on their spreadability. It was found that particle size distribution influenced the powder spreadability. Larger particles hindered the even spreading of powder over the base plate, resulting in low powder bed density and percentage coverage. This also correlated with the powders’ apparent densities. The flow rate and angle of repose gave an indication of how cohesive the powders are. The more cohesive a powder, the poorer the spreadability, resulting in a lower powder bed density and percentage coverage.
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    Evaluating the displacement field of paperboardpackages subjected to compression loading using digital image correlation (DIC)
    (Elsevier, 2020-09) Fadiji, Tobi; Coetzee, Corne J.; Opara, Umezuruike Linus
    Digital image correlation (DIC) is a full-field non-contact optical technique for measuring displacements in experimental testing based on correlating several digital images taken during the test, particularly images before and after deformation. Application of DIC cuts across several fields, particularly in experimental solid mechanics; however, its potential application to paperboard packaging has not been fully explored. To preserve fresh horticultural produce during postharvest handling, it is crucial to understand how the packages deform under mechanical loading. In this study, 3D digital image correlation with two cameras and stereovision was used to determine the full-field displacement of corrugated paperboard packaging subjected to compression loading. Strain fields were derived from the displacement fields. Results obtained from the displacement fields showed the initiation and development of the buckling behaviour of the carton panels. The displacement was observed to be largely heterogeneous. The displacement field in the horizontal direction was smaller compared to that of vertical and out-of-plane directions. In addition, the strain variation increased as load increased, which could be a precursor to material failure. The technique proved to be efficient in providing relevant information on the displacement and strain fields at the surface panels of corrugated paperboard packages used for handling horticultural produce. In addition, it offers prospects for improved mechanical design of fresh produce packaging.
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    Transient model and simulation of a single Effect water/lithium-bromide vapour absorption system
    (2016-12) Jeggels, D. H.; Dobson, R. T.; Mechanical and Mechatronic Engineering
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    Experimentally determined material parameters for temperature prediction of an automobile tire using finite element analysis
    (SAIMechE, 2019) Van Blommestein, W. B.; Venter, G.; Venter, M. P.
    The material parameters of an automotive truck tire were experimentally determined and validated for use in a thermal finite element analysis to determine the temperature distribution in the tire due to different operating conditions. Uni-axial tensile tests were performed on tire samples. The force displacement response of each was used to determine material properties by means of direct curve-fitting and iterative numerical procedures. Equivalent finite element simulation models were used to validate the properties. Hysteresis behaviour of the rubber regions were identified by dynamic mechanical analysis. Material definitions were incorporated into a finite element model to predict the steady-state heat generation and temperature distribution within a tire due to hysteresis. Experimental rolling tire temperature measurements were taken on a test bench. A comparison of the results with those obtained from the equivalent thermal models was used to validate the numerical models.
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    Peridynamic approach to predict ductile and mixed-mode failure
    (SAIMechE, 2019) Conradiea, J. H.; Becker, T. H.; Turner, D. Z.
    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, 𝑱ı𝖼. 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.