RESEARCH ON THE MECHANICAL CHARACTERISTICS OF LAMINATED SHALE BASED ON SCRATCH TESTS

Mechanical properties and microstructures of TiCN/nano-TiB2/TiN cermets prepared by spark plasma sintering

Using Deep Learning to Predict Fracture Patterns in Crystalline Solids

Objective:This study aimed to improve the mechanical properties of denture base material using various concentrations of natural biopolymer, i.e., Gum Arabic (GA).Methods:This experimental study was conducted at the Dental Health Department of the College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia from May 2022 to July 2022. After obtaining exemption from the institutional review board, the powdered GA was added in ratios of weight 5, 10, and 20% to PMMA heat-cured acrylic powder to produce bar-shaped samples (65 × 10 × 30 mm3 in dimensions). While the control group was prepared as such. Micro hardness (n=10/group) and fracture toughness (n=10/group) were evaluated. One-way analysis of variance method was used to statistically analyze the results (p<0.05) using SPSS version 23.Results:Significant differences were observed for micro hardness (p<0.001) and fracture toughness (p=0.007) between the means of the different study groups. The control group exhibited the highest micro hardness (22.5±0.6 VHN) and fracture toughness (1.25±0.11 MPa.m1/2) value among the study groups. While 20 wt. % GA and 10 wt. % GA groups showed the lowest micro hardness and fracture toughness values, respectively.Conclusions:GA powder might not be an appropriate reinforcing material for denture base or the higher filler loading of GA in denture base acrylic might be detrimental to the mechanical properties.

This study evaluated the effect of artificial saliva storage on the hardness, crack length, and fracture toughness of a glazed, polished, and bleached hydrothermal low-fusing glass-ceramic (Duceram LFC). Forty ceramic discs were constructed. The discs were assigned to four groups (n = 10) according to their surface finish: Gp1 -- Autoglaze, Gp2 -- Autoglaze/ground/diamond-polished, Gp3 -- Overglaze, Gp4 -- Overglaze/ground/diamond-polished. Each group was further divided into two subgroups forming eight total subgroups (n = 5). Subgroup A was unbleached; Subgroup B was bleached. Testing was performed before and after 21 days of artificial saliva storage. Data were presented as means and standard deviation (SD). ANOVA was used, along with Duncan's post hoc test for pairwise comparison between the means when ANOVA test was found significant (p< or = 0.05). Surface treatments such as glazing, polishing, and bleaching, saliva storage, and the interaction between these variables had a statistically significant effect on mean values of microhardness, crack length, and fracture toughness of the specimens. There was a statistically significant increase in microhardness and fracture toughness mean values, while crack length values decreased after saliva storage. Polished specimens recorded the smallest crack lengths and fracture toughness, and highest hardness values before and after saliva storage. No difference in fracture toughness values was evident between glazed and polished specimens. Mean crack lengths decreased after saliva storage in all the tested specimens. Hardness values increased after saliva storage. The autoglazed group showed significantly higher fracture toughness, lower crack length, and microhardness than the overglazed group. Surface finishing procedures and artificial saliva storage had a statistically significant effect on mean values of microhardness, crack length, and fracture toughness. This in vitro study suggests that fracture toughness of ceramics may be affected by different surface treatments such as glazing, polishing, bleaching, or a combination; however, in this study Duceram LFC proved its self-healing property after 3-week storage in artificial saliva.

This paper investigates high-maturity organic matter-rich shales with high clay mineral contents in the Qingshankou Formation, in the Gulong Depression of the Songliao Basin, at a sub-millimeter scale, using a new laminar division method based on XRF data. The influence of laminar structure on reservoir quality is examined using a combination of geochemistry, mineralogy, and pore structures. Explanatory models are established. Three types of laminar units are distinguished in the study area based on differences in pore structure. These are clay mineral laminae (UA), clay mineral-Ostracod laminae (UB), and clay mineral-felsic laminae (UC). UA has illite intergranular pores, micro-fractures, and organic pores, with diameters of 0.5~2 μm. UB primarily contains Ostracod shell margin fractures, pyrite intergranular pores, and chlorite intragranular pores. UC contains albite and illite intergranular pores. Nitrogen adsorption tests show that UA has the highest clay content and the best specific pore volume and specific surface area, indicating that clay minerals are the main contributors to the pores in this type of unit. 2D–3D models of different laminae reveal that carbonate cement is widely developed in UB and UC, but dissolution pores are less developed, with the result that the porosity of UA is two to three times greater than that of UB or UC. It appears that intergranular pores and fractures, formed during the transformation of clay minerals during the advanced thermal evolution stage, are the main contributors to storage space and flow channels. Thermal evolution, clay mineral transformation, and carbonate cementation are the key factors causing differences between laminar units. In addition, clay mineral laminae (UA) are the most important laminar units for shale oil enrichment in the study area. This finding is of great significance for accurately predicting the distribution of shale “sweet spots” and guiding shale oil and gas exploration.

In this investigation, fracture toughness behavior of high strength low alloy (HSLA) steel welded joint was studied using acoustic emission (AE) monitoring. For the design of new structures and for the safety and reliability analyses of operating components, fracture toughness (KIC) values of materials play an essential role. Acoustic emission technique (AET) has been used for determination of fracture toughness based on some observable changes of AE evolutions. However, the occurrence of appreciable plasticity in materials, the friction between the crack surfaces and mechanical noise could generate high emission and may result in some difficulties in precise determination of fracture toughness. Thus, the objective of this study is to propose a new approach to evaluate fracture toughness values and to characterize the fracture process based on AE entropy. Specimens were selected from 2.25Cr-1Mo-0.25V steel welded joint which were thermally aged at 978 K for 8 h. The AE signals generated during fracture processes were recorded and the corresponding AE entropy was calculated based on the probability amplitude distribution from each original AE waveform. The point of crack initiation was identified by the occurrence of sudden rise of AE entropy and the corresponding critical load was used to estimate fracture toughness value. The estimated values obtained from the proposed new approach were compared with those determined by the methodology proposed by compact tension specimen testing according to ASTM standard E399. The results showed that the estimated values were in close agreement with those gained from ASTM standard. It was concluded that AE entropy was an effective parameter to estimate fracture characteristics and fracture toughness values.

Evaluation of alternative polymer bracket materials

Spark plasma sintering of translucent polycrystalline α/β‐silicon nitride ceramics with Y2O3 additive

The influence of specimen design on plane strain fracture toughness (KIc) was studied by fracturing 2219-T87 aluminum and 5Al-2.5Sn ELI titanium alloy single-edge notched bend (SENB), single-edge notched tension (SENT), compact tension (CT), and surface flawed (SF) specimens at 72 F (295 K) in laboratory air, at -320 F (78 K) in liquid nitrogen, and at -423 F (20 K) in liquid hydrogen. Specimen thickness for all SENB, SENT, and CT specimens except titanium/room air specimens was approximately 2.5(KIc/σys)2 in. Specimen thickness for SF specimens ranged from 2.5(KIc/σys)2 to 0.25(KIc/σys)2. Relative orientations of crack propagation and rolling directions were identical in all specimens of a given alloy. For aluminum alloy specimens having thicknesses of 2.5(KIc/σys)2, SENB, SENT, and SF specimen tests yielded consistent fracture toughness values at all test temperatures whereas CT specimen tests always yielded lower fracture toughness. For titanium alloy specimens having thicknesses of 2.5(KIc/σys)2, SENB, SENT, CT, and SF specimen tests yielded consistent fracture toughness values at -423 F (20 K); at -320 F (78 K), fracture toughness values from SF specimen tests were significantly greater than those obtained from tests of other specimen types; at 72 F (295 K) no valid fracture toughness data were obtained. Both aluminum alloy SF specimen tests yielded consistent fracture toughness (KIE) values when both flaw depth and distance between flaw tip and back specimen face exceeded 0.5(KIE/σys)2.

The nil-ductility transition temperature (NDTT) test has been used extensively in naval ferritic steel applications since World War II. The use of the test results in fracture-safe design has extended into other structural steel industries, most notably those covered by the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. The construction of nuclear reactor pressure vessels, in accordance with the ASME code, requires material specifications that utilize both the NDTT and Charpy V-notch test data; coupling the NDTT and Charpy V-notch data results in a “reference” temperature (RTNDT), which is either greater than or equal to the NDTT. [The RTNDT is defined as being greater than or equal to the NDTT; at RTNDT plus 33°C (60°F), three Charpy V-notch specimen results must exhibit a minimum of 68 J (50 ft · lb) of absorbed energy and 0.89 mm (35 mil) of lateral expansion. The energy requirement generally governs except for irradiated materials.] Interestingly, some materials generally have an RTNDT based upon the NDTT, while others have an RTNDT consistently greater than the NDTT since the RTNDT is governed by the Charpy V-notch data; (that is, the temperature at 68 J (50 ft · lb) minus 33°C (60°F) is greater than the NDTT). For example, the RTNDT for SA533B-1 plate steel is generally set by the Charpy data, but the RTNDT for SA508-2 forging steel (which is similar to SA533B-1) is typically controlled by the measured NDTT. The science of fracture mechanics has also evolved since World War II, but the matching of transition temperature test results (NDTT, and RTNDT) with actual material fracture toughness (stress intensity) values is still uncertain. However, considerable progress in matching Charpy data with fracture toughness values has been made in recent years through the development of a large material property data base, which includes transition temperature and fracture toughness data. The work described in this paper builds on this research, and uses the same data base to examine the relationship between other transition temperature and toughness parameters. Computer modeling using stochastic procedures was employed to develop probability distributions which, by simulating the measurement of NDTT, clarify the interrelationships between NDTT, RTNDT, and fracture toughness. Predictions by the model of NDTT and RTNDT from dynamic fracture toughness data are in excellent agreement with measured values.

In this study, acoustic emission behavior of a tool steel during fracture toughness tests was investigated. Selected steel (AISI D2 cold-work tool steel) was heat treated at 5 different conditions (austenitized at 1010°C and tempered at 0, 300, 450, 525 and 575°C) and its properties were characterized using standard metallographic examinations, hardness and tensile tests. Compact specimen testing according to ASTM standard E 399 and acoustic emission technique were used to determine the fracture toughness value (KIC) and fracture process. Determination of fracture toughness using AE technique was carried out according to classical and two modified methods. Results showed that: (a) by increasing tempering temperature, plain strain fracture toughness (KIC) values and the fraction of ductile fibrous fracture increase except at 525°C when tempering process leads to secondary hardening, (b) fracture toughness values determined, using AE technique is lower than standard ASTM E399, (c) estimation of KIC values, using modified methods (AECR and AEER), is more accurate in comparison with the classical AE method and (d) the effect of tempering temperature on AE characteristics during fracture toughness test is similar to its effect on hardness.

Effects of cyclic freeze-thaw treatments on the fracture characteristics of sandstone under different fracture modes: Laboratory testing

Mechanistic interpretations of fracture toughness and correlations to wear behavior of hydroxyapatite and silica/hydroxyapatite filled bis-GMA/TEGDMA micro/hybrid dental restorative composites

Mining activities in open pit and underground mines will always be associated with rock breaking or stripping activities (both mechanical and blasting), so that this can affect the structure and strength of rocks. The strength of the rock is strongly influenced by the presence of initial cracks (pre-existing cracks) and rock anisotropy conditions associated with discontinuous plane conditions. Fracture mechanics is a science that illustrates how a fracture can occur and propagate during applied stress on material. The main parameter in fracture mechanics is called fracture toughness which shows the resistance of the material to propagate the crack. There are several mode in determining type I fracture toughness, one of which is type I fracture toughness Flattened Brazilian Disc (FBD) mode. Type I fracture toughness test is carried out using a compression machine in a laboratory and is conducted on concrete samples consisting of 3 (three) various samples, with a ratio of cement and sand composition of 1:1, 1:2, and 2:1. This test also uses different loading rate values, namely 2.50 mm/min, 2.70 mm/min, and 2.83 mm/min. The results of the type I fracture toughness value from each loading rate will be compared to determine the effect of the loading rate on the value of type I fracture toughness. The obtained fracture toughness value is also related to the physical and mechanical properties of the samples. Based on the results of tests, it can be seen that the loading rate affects the value of fracture toughness, the increase in fracture toughness value is followed by the higher loading rate. In addition, it can be seen that the fracture toughness value is directly proportional to the uniaxial compressive strength value and the indirect tensile strength value. The average correlation value obtained is R2 = 0.9884 (indicating a strong relationship).

Designing a simple and suitable laboratory test specimen for investigating the general mixed mode I/II/III fracture problem