Mechanical Properties of Bisacryl-, Composite-, and Ceramic-resin Restorative Materials

SUMMARY Objective: Resin-based materials used in restorative dentistry are introduced at a fast pace with limited knowledge about their properties. Comparing properties of these materials from different restorative categories is lacking but can help the clinician in material selection. This study aimed to compare mechanical properties and wear resistance of bis-acryl-, composite-, and ceramic-resin restorative materials. Methods and Materials: Bisacryl-resin (Bis-R, LuxaCrown, DMG), composite-resin (Com-R, Filtek Supreme Ultra, 3M Oral Care), and ceramic-resin (Cer-R, Enamic, VITA Zahnfabrik) specimens were prepared for mechanical tests: fracture toughness (FT) with and without initial thermomechanical loading using a mastication simulator, flexural strength (FS), and flexural modulus (FM), compressive strength (CS), and volumetric wear loss measurement. The datasets for FT and wear resistance were each analyzed using two-way ANOVA followed by pairwise comparisons or Tukey testing as appropriate. The datasets for FS, FM, and CS were analyzed using one-way ANOVA followed by the Tukey test. Results: Analysis of FS, FM, and CS showed significant differences between materials, with all pairwise comparisons between materials showing significance. Analysis of FT resulted in a significant interaction between the material and treatment, with analysis of wear loss showing a significant interaction between the material and the number of cycles. Conclusions: Cer-R demonstrated superior FT, CS, and wear resistance compared to Bis-R and Comp-R materials. Fracture toughness of Bis-R increased after thermomechanical loading.

A Quantified Study of the Resistance of Duplex Stainless Steels to HISC: Part 2 - Significance of the hydrogen permeation properties and severity of stress raisers, on hydrogen transport and cracking

The quantified microstructural analysis carried out on a wrought and a hot isostatically-pressed (HIP) UNS S31803 duplex stainless steel (DSS) in the Part 1 publication of this study 1, established the significance of the three-dimensional (3D) distribution and morphology/geometry of the ferrite and austenite phases on hydrogen transport through two DSS product forms. This paper is a follow-on to Part 1, and focuses on the role of the other two key, interrelated components of hydrogen-induced stress cracking (HISC): stress/strain, and hydrogen. For this purpose, experimental hydrogen permeation measurements, and environmental fracture toughness testing (i.e. J R-curve testing) using conventional and non-standard single-edge notched bend test specimens were used. These particularly enabled interpretation of the hydrogen permeation and transport test data, and evaluation of suitability of environmental fracture toughness test methods for the assessment of resistance to HISC in DSSs. The latter is discussed, both from laboratory and component integrity perspectives, in the context of the findings from the 3D microstructural characterisation of the two phases, the role of stress raisers and their severity, and hydrogen transport through the bulk and from the surface.

Fracture behaviors of HVFA-SCC mixed with seawater and sea-sand under three-point bending

This paper aims to study the fracture behaviors of high-volume fly ash-self-compacting concrete (HVFA-SCC) mixed with seawater and sea-sand (SWSS) or freshwater and river sand (FWRS). Three-point bending test were performed on 24 notched beams fabricated with varying in replacement ratio of fly ash (0%, 30%, 50%, and 70%) and the type of water and sand (SWSS and FWRS). The initial and unstable fracture toughness of these test specimens are determined by the double- K fracture model. The effect of fly ash replacement ratio and type of water and sand on the fracture parameters is analyzed and discussed. In addition, the cohesive fracture toughness of all the test specimens is calculated by using Gauss–Chebyshev integral method and the weight function method based on the bilinear tensile softening curve given in CEP-FIP Model Code. A comparison of fracture toughness parameters of determined from the experimental approach and analytical approaches is presented in these SCC specimens. Results show that SCC mixed with SWSS replacing FWRS can improve the unstable fracture toughness and fracture energy, and decrease its brittleness behavior. The cohesive fracture toughness of SWSS-SCC specimens is underestimated by these analytical methods based on the tensile softening curve given in CEP-FIP Model Code.

Microstructure and Fracture Toughness of Nitrided D2 Steels Using Potential-Controlled Nitriding

Potential-controlled nitriding is an effective technique for enhancing the life of steel molds and dies by improving their surface hardness and toughness against fatigue damage. In this study, the effect of the nitriding potential on the microstructure and fracture toughness of nitrided AISI D2 steels was investigated. The nitrided layers were characterized by microhardness measurements, optical microscopy, and scanning electron microscopy, and their phases were identified by X-ray and electron backscatter diffraction. As the nitriding potential increased to 2.0 atm−1/2, an increase in the surface hardness and fracture toughness was observed with the growth of the compound layer. However, both the surface hardness and the fracture toughness decreased at the higher nitriding potential of 5.0 atm−1/2 owing to the increased porosity in the compound layers, which mainly consist of the ε (Fe2–3N) phase. Additionally, by observing crack growth behavior, the fracture toughness was analyzed considering the material characteristics of the diffusion and compound layers. The fracture toughness was influenced by the location of the initial Palmqvist cracks due to the localized plastic deformation of the diffusion layer and increased crack length due to the porous compound layer.

Development of Al-SiC composite material from rice husk and its parametric assessment

In this research work, the development of Al-SiC composite material from rice husk and its parametric assessment is done using a CNC milling machine. They are further surface characterized, and mechanical properties such as BET surface area, SEM-EDX, and XRD, fracture toughness, tensile, and bending strength are studied. The machinability of the components is investigated for selected values of input-output parameters. Three castings, each with different particulate reinforcement combinations, are made with aluminum alloy (6061) using the stir casting method. BET surface area of extracted silica and Al-SiC composite material was found 374 m2/g and 150 m2/g, respectively. From results of BET surface area revealed that silica obtained from rice husk is more heterogeneous with a large surface area. A heterogeneous surface with larger pores was found through SEM images. XRD diffraction peaks show changes of amorphous silica into crystallinity in the composite material. The results also indicate that fracture toughness is very good at low temperatures and good machinability on CNC milling machines makes it suitable for aerospace applications.