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.

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.

High performance carbon fibre/epoxy composites, which are increasingly used for structural applications are susceptible to delamination. In response to this problem, the mode I INTERLAMINAR FRACTURE TOUGHNESS of unidirectional carbon/epoxy laminates has been studied under tensile loading by using a double cantilever beam (DCB) specimen. The FRACTURE energy is deduced from the data according to the area and the compliance methods. The morphology was explained through thermal analysis using DMA and fractography from scanning electron microscopy (SEM). Results showed improvement in high temperature moulding compound (HTM) system with 180°C cure in terms of INTERLAMINAR FRACTURE TOUGHNESS. There is also an improvement in MTM and LTM systems. SEM micrographs revealed their excellent delamination resistance as good crack stoppers with the evidence of strong fibre/matrix interface. For MTM systems GIc values dropped after post curing. This reduction was significant for MTM49-3 but not so much in the case of MTM49-7 laminate. On the other hand, the GIc for LTM45-1 did not seem to be affected by post curing at elevated temperature.

In this study, delamination of the corrugated composite plates made of unidirectional glass fibers and polyester resin has been investigated. The samples are fabricated by hand lay-up process based on the ASTM-D5528 standard. Using experimental tests, the strain energy release rate in mode I has been calculated for composite corrugated specimens by the prevalent method of INTERLAMINAR failure. Also, the samples were simulated as a double cantilever beam by Abaqus software, and the mechanical properties of unidirectional glass/polyester composite and the results of the numerical solution are also obtained. FRACTURE surfaces of experimental samples were analyzed by scanning electron microscope. Force-displacement curves obtained from experimental and numerical methods have been compared to find the material behavior and calculate the strain energy release rate for different samples with three pre-crack lengths. The results show that the corrugated composite plates have a higher INTERLAMINAR FRACTURE TOUGHNESS rather than flat samples and the four-wave sample with a crack length of 60 and 65 mm has the highest values of the strain energy rate released, equal to 963.77  J/m2 and 705.95  J/m2, respectively.

In recent years, the application of composite materials in aircraft and space vehicle structural components has become increasingly popular. Preventing failure of composite structural systems has been an important issue in engineering design. Due to the lack of through-the-thickness reinforcement, structures made from laminated composite materials and adhesively bonded joints are highly susceptible to failure caused by interfacial crack initiation and growth. The delamination phenomenon in a laminated composite structure may reduce the structural stiffness and strength and redistribute the load in a way that the structural failure is delayed or may lead to structural collapse. As the most application of these materials is in space structures, the failure of a composite structure component can lead to a catastrophic failure of the structure as whole, thus, an accurate quantitative measurement and understanding of damage and determination of remaining useful service life plays a vital role in prediction of failure of such structures. To do so, first, the FRACTURE properties of material should be determined. To calculate these properties, there are several experimental methods. Among them, the modified Arcan test is one of the most apposite methods for in-plane mixed-mode loading condition. In this investigation, a new specimen has been introduced to reduce cost and problems concerning utilization of adhesively. The critical FRACTURE parameters of carbon-epoxy woven laminated composite material, which is of paramount materials in industry, in room temperatures is calculated both with experimental and numerical methods. These parameters include the critical stress intensity factors and critical strain energy release rate on crack tip. The geometric correction factors for modified Arcan test are calculated with a 2D finite element analysis. Finally, the values of critical FRACTURE properties are calculated using these geometric modification factors and critical loads generated via experimental procedure.

Laminated composite materials are susceptible to damage, such as delamination, due to poor out-of-plane properties and inadequate adhesion at the layer interface. Using the interlayering method is an effective way to enhance resistance against delamination in these materials. However, interlayer synthesis methods have been limited and sometimes very expensive. Therefore, this study investigates the impact of novel 3D-printed polyvinyl alcohol (PVA) interlayers on the mode II INTERLAMINAR FRACTURE TOUGHNESS in glass/epoxy laminated composites. Notably, the interlayers feature a geometrical structure consisting of square cell shapes, allowing the filament to have an equal volume percentage to the resin in the interlayer. To achieve this, end-notch flexure specimens (ENF) were prepared, and the mode II INTERLAMINAR FRACTURE TOUGHNESS was calculated using the compliance-based beam method (CBBM). The specimens' crack growth resistance curve (R-curve) analysis revealed that using the desired 3D-printed interlayer increases the mode II INTERLAMINAR FRACTURE TOUGHNESS by 73%. Furthermore, the behavior of crack growth resistance in laminated composites reinforced with 3D-printed interlayer shows an increasing trend. The mode II FRACTURE surface analysis of reinforced specimens demonstrates the influence of square cell shapes in creating shear hackles, increasing surface friction at the interface of laminated composite layers, crack pinning mechanism, and changing the direction of crack growth, ultimately leading to increased resistance to crack growth.

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.