To investigate the dynamic behavior of granular materials under repeated impact loading, repeated compression tests were conducted on sandy soil and silica sand using an improved Φ40 mm split Hopkinson pressure bar (SHPB) setup. The study systematically examined the evolution of material density, particle breakage, stress wave propagation, stress–strain response, and energy dissipation characteristics. The results indicate that the density of both materials increases gradually with the number of impacts and eventually stabilizes. The median particle size of sandy soil decreases by only approximately 25 %, whereas that of silica sand reduces by up to 65.6 %. After five impacts, the relative breakage indices of sandy soil and silica sand are 0.05 and 0.23, respectively, indicating a more pronounced particle refinement effect in silica sand. Wave velocity measurements show that both the compression wave and peak stress velocities of sandy soil are more sensitive to densification, while silica sand exhibits limited increases in wave velocity due to severe particle breakage. Regarding stress–strain behavior, both materials undergo elastic, plastic, yielding, and strain-hardening stages, with overall stress levels shifting upward as the number of impacts increases. However, due to particle breakage, silica sand exhibits greater energy dissipation, resulting in lower stress levels under the same strain compared to sandy soil. Energy analysis reveals that the energy absorption density of both materials first increases and then decreases with initial density. Notably, silica sand demonstrates more stable and progressively enhanced energy dissipation over five impacts, making it more suitable for protective applications under repeated impact loading. The findings provide experimental evidence and theoretical support for the design and application of granular materials in protective engineering and related cushioning structures.
The primary aim of this in vitro study was to compare enamel surface morphology following standardized artificial demineralization among five protective dental materials and an untreated control. Specifically, scanning electron microscopy (SEM) was used to characterize acid-exposed and wax-protected enamel regions and to compare five-point ordinal surface-preservation scores across the six experimental groups. Fifty-four human premolars extracted for orthodontic reasons provided 108 enamel surfaces. A 2 × 3 mm window was prepared on each surface, and specimens were randomly assigned to six groups (n = 18): control, APF gel containing 1.23 % fluoride ions, Enamel Pro Varnish containing 5 % sodium fluoride (NaF), Enamel Pro Prophy Paste with ACP, fluoride-releasing light-cured Pro Seal, and Duraphat containing 5 % sodium fluoride (NaF). Specimens were stored in artificial saliva and exposed to an artificial caries solution at pH 4.4 twice daily for 1 h over 30 days. After cycling, the surfaces were examined by SEM at ×500 and ×1500 magnifications. Images were morphologically classified and rated using a five-point ordinal surface-preservation scale, in which lower scores indicated better preservation. Data were analysed using the Kruskal–Wallis test followed by Holm-adjusted Dunn comparisons. Mean ordinal SEM scores were 5.00, 3.72, 2.06, 3.06, 3.50, and 3.56 for Groups A–F, respectively, with an overall group difference (H(5) = 68.32, p < 0.001). Enamel Pro Varnish had the lowest mean ordinal SEM score (2.06), although its difference from Group D was not statistically significant after Holm adjustment (p = 0.115). Although all treated groups had more favourable ordinal SEM scores than the control, none reproduced the SEM appearance of untreated sound enamel.
This study investigates the prediction of the compressive strength of activated binary cement mortars containing ground granulated blast-furnace slag (GGBFS) using two complementary modelling approaches: response surface methodology (RSM) and an artificial neural network (ANN). A database of 96 mix–curing combinations was assembled from the published literature on activated slag cement systems. Four input parameters were considered: slag replacement ratio (0–70 %), slag fineness (Blaine, 320–650 m²/kg), curing temperature (20–80 °C) and curing time (1–90 days). The output variable was the 1- to 90-day compressive strength (9–64 MPa). A second-order RSM polynomial was fitted and analysed by ANOVA, while a back-propagation feed-forward ANN with a 4–9–6–1 architecture and hyperbolic tangent activation was trained using the L-BFGS algorithm. The ANN reached R² = 0.996 and RMSE = 0.92 MPa over the whole dataset, clearly outperforming the RSM model (R² = 0.785, RMSE = 6.83 MPa). Sensitivity analysis showed that curing time was the dominant predictor (62 %), followed by slag fineness (22 %), curing temperature (8 %) and slag replacement ratio (8 %). The results confirm that ANN is a more reliable surrogate for the highly non-linear hydration kinetics of activated slag mortars and can be used to support mix-design decisions and reduce experimental effort.
Zinc is important in many applications due to its resistance to corrosion under different conditions; it is used in galvanization. This article presents a study of zinc from remelting waste zinc (waste collected from manufacturing scrap ; galvanizing zinc) and recycled by sand casting, then heat treated under different conditions. Impact and hardness testing ascertained the mechanical properties of the zinc casting, while optical microscopy characterized its microstructure. The study found that the grain growth increased after natural aging and reached a maximum of approximately 41 % of the treatment at 350 °C, for 3 h followed by water quenching, which exhibited the largest grain size, indicating significant grain growth. In contrast, the treatment at 350 °C, for 5 h followed by water quenching refined the grain structure and reduced the precipitation fraction, suggesting a more stable microstructure. The as-cast sample exhibited the highest hardness (approximately 94 HV), whereas heat treatment initially reduced hardness because of microstructural contrast dissolution during solution treatment. Among the heat-treated specimens, the treatment at 350 °C, for 5 h followed by water quenching, produced the highest hardness (approximately 82 HV), indicating an effective balance between precipitation strengthening and grain refinement. Specimens showed intermediate hardness values in the heat treatment at 370 °C for 3 h and 5 h, then aged at 180 °C for 90 min, which are attributed to grain growth during aging. The results demonstrate that heat treatment significantly affects the precipitation behavior, grain evolution, and hardness of high-purity zinc, with the treatment at 370 °C, for 5 h followed by water quenching providing the most favorable combination of microstructural stability and mechanical performance. The impact strength was strongly influenced by the heat treatment condition, with the heat treatment at 370 °C for 5 h, then aged at 180 °C for 90 min achieving the highest value of 5 J/cm², comparable to commercial ZP3 (Zamak 3) and higher than ZP5 (Zamak 5).
The aim of this in vitro study was to compare the relative translucency parameter (RTP), contrast ratio (CR), and opalescence parameter (OP) of selected commercial translucent CAD-CAM zirconia materials. Three Computer-Aided Design – Computer-Aided Manufacturing (CAD-CAM) zirconia materials were evaluated: Katana UTML, InCoris TZI C, and Cercon XT. Thirty-six A2-shade specimens with dimensions of 10 × 12 mm and a final thickness of 1.00 ± 0.05 mm were prepared. Color coordinates were measured on standardized black and white backgrounds using a digital spectrophotometer. RTP was calculated using the CIEDE2000 formula, CR was determined from reflectance values, and OP was calculated from differences in a* and b* coordinates. The data were analyzed using one-way analysis of variance followed by the Bonferroni post hoc test. Significant differences were found among the materials for RTP, CR, and OP. Katana UTML showed significantly higher RTP and lower CR values than InCoris TZI C and Cercon XT. However, Katana UTML showed significantly lower OP values. These findings indicate that translucency and opalescence do not necessarily change in parallel. RTP, CR, and OP should therefore be considered together when selecting zirconia materials for esthetic restorations.
