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.

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.  

Mode I fracture toughness of carbon/ glass reinforced polyster hybrid composite was invesitigated expermrntally and numerically by using the cosmos)/m 2.6 finite element software (fms) by utulizing the hand laup techniqe)(HLU). The single edge notch bending (SENB) test was developed to evalute the mode l fracture toughness of carbon composites, glass composite and hybrid compodite materials at varuos fiber configurations. Scaning electron microscope (SEM) was used to examine the fracture surface of the hybrid composite material under the effect of mode l loading. the expermental result showed the maximum stress intensity (sif) factor 882mpa. mm1/2. obtained in the hybrid composite with stacking dequencess (c/g/g/c) during the mode l loading compared to other stacking sequences. this is attributed to the goid interfical between the carbon and glass fibers and matrix face. From the resukts, it was suggested that the expermental results is a goid a gremnent with the finite element modelling

This research work presents the study on fracture behavior of Al6061 with graphite particulate composite produced by the stir casting technique. The materials selected for the proposed work is Al6061 and graphite particles. Compact tension (CT) specimens were utilized to determine fracture toughness for different thickness of composite. In the present work, optimizing the parameters of the compact tension specimens is carried out using Taguchi method. Four parameters and two factors are considered to optimize the parameters. Factors considered are material composition and a/W ratio. From the Taguchi analysis, on compact tension specimens, Al6061-9%graphite is the optimized composition and fracture toughness is maximum for a/W ratio = 0. 45. All the compact tension specimens of different thickness (B = 4, 5, 7, 10, 12, 15, 18 and 20mm) of a/W=0. 45 were tested to find the fracture toughness. From the results, it was observed that the Kq reduces with increment in thickness to width (B/W) proportions and found to stay consistent for B/W≥ 0. 3. This consistent estimation of Kq for B/W≥ 0. 3 prevail the plane strain fracture toughness (KIc) of the composite.

The effects of carbon equivalents of 2.3, 3.3 and 4.3% on the microstructure, hardness and fracture toughness of a low alloyed ductile cast iron in as cast, annealed, normalized and austempered conditions have been investigated. fracture toughness was measured using a plain-strain fracture toughness (kIc) test and also J-Integral approach. The results show that the pearlite content increases as the CE decreases from 4.3 to 2.3% The nodularity and nodule count also decrease with decreasing the CE%. The annealed samples show a predominantly ferritic structure. Iron with 2.3 CE% shows pearlitic microstructure. The austempered microstructure contains bainitic ferrite and retained austenite at all carbon equivalents. The fracture toughness value (kQ and kIc) of ductile iron increases with increasing the CE% in all conditions and a maximum value is obtained in austempered condition. The hardness decreases with increasing CE% and an maximum value of 526 HV50 can be obtained at 2.3 CE% in a austempered condition. The SEM study shows that all the fractures of austempered specimens are ductile in nature whilst all that of normalized condition are brittle. fracture behavior of 4.3 CE% ductile iron in as cast and annealed conditions are ductile where those of 2.3% are brittle. The iron with 3.3% shows a brittle fracture in as cast condition and a ductile fracture in annealed condition. The results show that J. integral approach can be used in measuring of kIc, particulary if the kIc values can not be achieved.

An epoxy resin was modified by silica nanoparticles and cured with an anhydride. The particles with different batches of 12, 20, and 40 nm sizes were each distributed into the epoxy resin ultrasonically. Electron microscopy images showed that the silica particles were well dispersed throughout the resin.Tensile test results showed that Young’s modulus and tensile strength increased with the volume fraction and surface area of the silica particles. The simultaneous use of two average sizes of 20 and 40 nm diameter silica particles still increased these mechanical properties but other combinations of silica particles were unsuccessful.A three-point bending test on each pre-cracked specimen was performed to measure the mode I fracture toughness energy. The fracture energy increased from 283 J/m2 for the unmodified epoxy to about 740 J/m2 for the epoxy with 4.5 wt% of 12 nm diameter silica nanoparticles. The fracture energy of smaller particles was greater because of their higher surface to volume ratio. The fracture energy results showed also that the combined nanoparticles has a synergic effect on the fracture toughness of nanocomposites. Simultaneous use of 10 and 20 nm particles increased the fracture energy to about 770 J/m2. Finally, crack-opening displacement was calculated and found to be in the range of several micrometers which was much larger than the sizes of particles studied. Thus, the toughening mechanisms of crack pinning and crack deflection have a negligible effect on improvement of toughness, nevertheless, the plastic deformation and plastic void growth are dominant mechanisms in epoxy toughening by nanoparticles.

The interlaminar fracture behaviour of unidirectional carbon/epoxy composites has been studied under flexural loading by using end-notched flexure (ENF) specimens. GIIc Values were calculated as total fracture toughness energy at the maximum load sustained by the materials as the delamination extended. The results showed that high temperature moulding systems (XHTM45) have the highest GIIc values well above 1000 J/m2. For medium temperature systems (MTM) GIIc have also increased significantly after post cure. For compression strength after impact (CSAI), the behaviour to a certain extent is related to that found for GIIc tests. Comparison of the GIIc values with CSAI also indicated a relationship between two test results. SEM Micrographs revealed their excellent delamination resistance as good crack stoppers with the evidence of strong fibre/matrix interface. Dynamic mechanical analysis (DMA) indicated the increased Tg and modulus retention of the LTM and MTM prepregs after post curing at elevated temperatures. The failure mechanisms seem to be different for different tough matrix materials and appear to be strongly dependent on the cure and post-curing conditions. This is particularly noticeable for curing at 135°C and 80°C. of medium and low temperature moulding systems.