Statement of Problem: In a previous study it was reported that a durable resin-ceramic tensile bond could be obtained by an appropriate silane application without the need for HF acid etching the ceramic surface. Evaluation of the appropriate application of silane by other test methods seems to be necessary.Purpose: The purpose of this study was to compare the interfacial Fracture toughness of smooth and roughened ceramic surfaces bonded with a luting resin.Materials and Methods: Ceramic discs of 10 mm in diameter and 2 mm in thickness were prepared.Four different surface preparations (n=10) were carried out consisting of (1) ceramic surface polished to a 1µm finish, (2) gritblasted with 50µm alumina, (3) etched with 10% HF for 2 min, and (4) gritblasted and etched. The ceramic discs were then embedded in PMMA resin. For the adhesive area, the discs were masked with Teflon tapes. A circular hole with diameter of 3 mm and chevron-shaped with a 90° angle was punched into a piece of Teflon tape. The exposed ceramic surfaces were treated by an optimised silane treatment followed by an unfilled resin and then a luting resin cylinder of 4mm in diameter and 11 mm in length was built. Specimens were stored in two different storage conditions: (A): Distilled water at 37°C for 24 hours and (B): Distilled water at 37°C for 30 days. The interfacial Fracture toughness (GIC) was measured at a cross-head speed of 1 mm/min. The mode of failure was examined under a stereo-zoom microscope and Fracture surfaces were examined under Scanning Electron Microscope.Results: The mean interfacial Fracture toughness values were; Group A: 1) 317.1±114.8, 2) 304.5±109.2, 3) 364.5±169.8, and 4) 379.4±127.8 J/m2±SD. Group B: 1) 255.6±134.4, 2) 648.0±185.1, 3) 629.3±182.6 and 4) 639.9 ±489.0 J/m2±SD. One way Analysis of Variance showed that there was no statistically significant difference in the mean interfacial Fracture toughness for groups A1-A4 (P>0.05). However, the mean interfacial Fracture toughness for group B1 was significantly different from that for groups B2, B3 and B4 (P<0.05). Independent-ٍٍٍSamples T-Test results showed that there was a significant increase in the GIC mean value for groups B2 and B3 after 30 days water storage (P<0.05). The modes of failure were predominantly interfacial or cohesive within the resin.Conclusions: The Fracture toughness test method used in this study would be appropriate for analysis of the adhesive zone of resin-ceramic systems. From the results, it can be concluded that micro-mechanical retention by gritblasting the ceramic surfaces could be sufficient with no need for HF acid etching the ceramic surfaces when an appropriate silane application procedure is used.

Self-compacting lightweight concrete (SCLC) is one type of concrete that its usage has widely increased. The use of some additives in the production of SCLC can both reduce its costs and improve its properties. The effects of different cement replacement materials have been studied by several researchers. Jalal et al. (2012) claimed that the use of silica fume could improve the electrical resistance and mechanical properties of self-compacting concrete, and reduce its water absorption. Moreover, the use of silica fume in normal concrete improves the bond between aggregate and paste surfaces, and it has positive effects on Fracture toughness, compressive strength and tensile strength (Lam et al., 1998). To simulate the Fracture behavior of concrete in numerical models of concrete, depending on the model, some parameters such as Fracture energy, Fracture toughness and critical effective crack-tip opening displacement ( or δc), which generally are known as Fracture parameters, must be determined. In this regard, Peterson (1980) showed that the Fracture parameters are significantly affected by water to cement ratio (w/c) and the quality of aggregate. In other words, by reducing w/c or using stronger aggregate, the Fracture energy of concrete increases. In this study, the effect of w/c and silica fume on the Fracture toughness and Fracture energy of SCLC has been investigated. Therefore, by making six mix designs and 126 concrete specimens, Fracture parameters, mechanical properties and the workability of fresh concrete were carefully studied. Initially, four mix designs with the w/c of 0.37, 0.42, 0.47 and 0.52 were made. Afterwards, by replacing 0, 5% and 10% of the weight of cement with silica fume, the effects of changing this parameter on the Fracture parameters of SCLC were studied.

The Fracture energy of the concrete is an important parameter which can be used to identify the Fracture process of concrete members, especially when subjected to tension and flexural loading. Practices to measure this property in experiments can be expensive and time-consuming. In this study, a statistical model using Linear Genetic Programming is introduced to predict concretes' Fracture energy with three readily measured input parameters, namely, compressive strength, maximum aggregate size, and water to cemented ratio. The model was developed and trained based on a dataset of 64 measured experimental values taken from published research. The performance of the model was evaluated using statistical indices such as the coefficient of determination, root mean squared error, and mean absolute error, and compared with previously proposed empirical models. The experimental results show that the proposed LGP- based model is superior to old regression-based equations in accuracy and generalization. This model can be a useful methodology for engineers in design and analysis, minimizing the need for large amount of laboratory testing.

This work presents the hollow center cracked disc (HCCD) test and the cracked straight through Brazilian disc (CSTBD) test of oil well cement sheath using the experimental test and Particle Flow Code in two-dimensions (PFC2D) in order to determine mode I Fracture toughness of cement sheath. The tensile strength of cement sheath is 1.2 MPa. The cement sheath model is calibrated by outputs of the experimental test. Secondly, the numerical HCCD model and CSTBD model with diameter of 100 mm are prepared. The notch lengths are 10 mm, 20 mm, 30 mm, and 40 mm. The tests are performed by the loading rate of 0.018 mm/s. When the notch length in CSTBD is 40 mm, the external work is decreased 48%, related to the maximum external work of model with notch length of 10 mm (0.225 KN*mm decreased to 0.116 KN*mm). When the notch length in HCCD is 30 mm, the external work is decreased 33%, related to the maximum external work of model with notch length of 10 mm (0.06 KN*mm decreased to 0.04 KN*mm). The Fracture energy is largely related to the joint length. The Fracture energy is decreased by increasing the notch length. In constant to the notch length, the Fracture energy of the CSTBD model is more than the HCCD model. Mode I Fracture toughness is constant by increasing the notch length. The HCCD test and the CSTBD test yield a similar Fracture toughness due to a similar tensile stress distribution on failure surface. The experimental outputs are in accordance to the numerical results.

The onshore oil and natural gas industries of China have started a large-scale development when crude oil reserves have been difficult to recover. The stratum Fracture modification is an indispensable measure to efficiently develop oil and gas fields. Hydraulic fracturing is the most important reservoir stimulation technique, but it is still faced with various problems such as the failure to Fracture the target reservoir, long fracturing duration, and short efficient length of the Fracture. High energy Gas Fracturing (HEGF) can easily break down the high-Fracture-pressure oil reservoir and generate multiple Fractures free of in-situ stress. Moreover, HEGF entails no large-scale devices, and this method is strongly adaptable to the environment without causing environmental pollution. After combining the two technologies (HEGF and the other), then they can complement each other with their strengths. That is, both of them decrease the Fracture initiation pressure of (or caused by) hydraulic fracturing on the one hand, and to extend, gather, and support multiple radial Fractures of gas fracturing on the other hand. Thus, a Fracture zone with a large radius is finally formed, and the percolating resistance of the fluid is significantly decreased. Moreover, in this study, a dynamic model related to the drainage flow of the perforated holes in a gas well, fluid pressure distribution in the Fracture, fluid seepage on the Fracture wall, Fracture initiation criterion, and Fracture propagation velocity during the HEGF process has been presented. Consequently, a gas/liquid/solid coupling Fracture dynamic propagation model during the HEGF process can be built to provide a theoretical basis for the accurate simulation of the Fracture form changes during this process.

Statement of Problem: Evaluation of Fracture properties is a basic principle for true assessment of brittle materials’ properties. Resin–based composite materials are being used extensively in today’s dentistry. Fracture toughness is considered an important parameter for providing useful information about material’s nature, properties and its resistance to Fracture. Purpose: The purpose of this study was to evaluate the Fracture toughness of a resin composite produced in the country and to compare it with that of other standard materials. Materials and Methods: Four types of resin composite materials were used as follow to prepare 60 specimens (n=15 for each group), A) Tetric Ceram (Ivoclar–Vivadent); B) Brilliant (Coltene-Whaledent); C) SpectrumTPH (Dentsply); and D) Ideal Macoo (Ideal Macoo, Iran). Specimens of 5 mm diameter (± 0.1 mm) and 2 mm depth (±0.1 mm) were prepared in a central notch (90° notch angle) PTFE mold. Then specimens were light cured with two applications of overlapping exposures for a total of 120 s and were stored in distilled water at 37ºC for 48 hours, A cylindrical roller of 3 mm diameter was seated inside the V sections and Fracture was accomplished in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed by one–way ANOVA and post-hoc paired Tukey HSD test with P<0.05 as the limit of significance. Results: The mean KIC and torque to Fracture (T) values for each material tested were; A) 3.08±0.42, 16.99±2.34, B) 2.88±0.63, 16.04±1.98; C) 3.40±0.53, 18.75±2.93 and D) 2.87±0.46, 15.78±2.57 MN/m3/2±SD and N/mm±SD, respectively. Group C showed significantly the highest mean KIC and T values among groups tested which was significantly higher than that of group B and D (P<0.05). The mean KIC and T values for groups A, B, and D were not significantly different (P>0.05). Conclusion: From evaluating the Fracture properties of materials tested in this study it was concluded that the mean Fracture toughness value for SpectrumTPH (Dentsply) was significantly higher than that of Ideal Macoo resin composite material (Ideal Macoo, Iran). The F.T value for Ideal Macoo was considered acceptable as it was not significantly different from that of other resin composite materials tested.  

Distal femoral Fracture with intramedullary nail in situ is a rare situation. We report here a case of healed femoral shaft Fracture with intramedullary nailing for three years, who has recently had an un-comminuted supracondylar re-Fracture with nail tip cut-out as a result of minor trauma in the presence of osteoporosis.