Double Cleavage Drilled Compression Specimen Research Articles

Quantitative Analysis of Crack Closure Driven by Laplace Pressure in Silica Glass

Crack tips in silica glass in moist atmosphere are filled with an equilibrium liquid condensation of a few hundred nanometers length. Not only does this local environment affect the chemistry of slow crack propagation by stress corrosion, but it also has an important mechanical effect due to its highly negative Laplace pressure. The present article presents an original technique for measuring the physical properties of the liquid condensation in terms of the Laplace pressure and critical condensation distance. This is achieved by combining in situ atomic force microscopy measurements of the condensate length and optical determination of the crack closure threshold in a double cleavage drilled compression specimen.

Numerical analysis of an improved DCDC specimen for investigating mixed mode fracture in ceramic materials

Double cleavage drilled compression (DCDC) specimen, on account of its specific fracture parameters and also strong crack path stability, is frequently used in crack growth studies of brittle materials such as ceramics and glasses. Various configurations of this specimen have been developed and studied in the past in order to determine fracture parameters in different loading conditions. In this paper, an improved DCDC specimen is proposed by means of some geometrical modifications applied to the standard DCDC configuration. Finite element analyses indicate that contrary to all previous DCDC configurations, the new version has the distinct potential to provide the entire span of practical loading condition from pure mode I to pure mode II. It is also shown that the T-stress term is strongly negative in this specimen. Using a generalized maximum tangential stress (MTS) criterion, the T-stress effects on fracture initiation of the proposed specimen are investigated analytically.

Crack opening profile in DCDC specimen

The opening profile of the cracks produced in the Double Cleavage Drilled Compression (DCDC) specimens for brittle materials is investigated. The study is achieved by combining Finite element simulations of a DCDC linear elastic medium with experimental measurements by crack opening interferometry on pure silica glass samples. We show that the shape of the crack can be described by a simple expression as a function of the geometrical parameters of the sample and the external loading conditions. This result can be used to measure accurately in real time relevant quantities during DCDC experiments, such as the crack length or the stress intensity factor applied to the specimen.

Brittle fracture analysis of the offset-crack DCDC specimen

Applications of fracture mechanics in the strength analysis of ceramic materials have been lately studied by many researchers. Various test specimens have been proposed in order to investigate the fracture resistance of cracked bodies under mixed mode conditions. Double Cleavage Drilled Compression (DCDC) specimen, with a hole offset from the centerline is a configuration that is frequently used in subcritical crack growth studies of ceramics and glasses. This specimen exhibits a strong crack path stability that is due to the strongly negative T-stress term. In this paper the maximum tensile stress (MTS) criterion is employed for investigating theoretically the initiation of brittle fracture in the DCDC specimen under mixed mode conditions. It is shown that the T-stress has a significant influence on the predicted fracture load and the crack initiation angle. The theoretical results suggest that brittle fracture in the DCDC specimen is controlled by a combination of the singular stresses (characterized by KI and KII) and the non-singular stress term, T-stress.

In-situ crack propagation observation of a particle reinforced polymer composite using the double cleavage drilled compression specimens

In this study, we investigate the feasibility of in-situ crack propagation by using a double cleavage drilled compression (DCDC) specimen showing a slow crack velocity down to 0.03 mm/s under 0.01 mm/s of displacement control. Finite element analysis predicted that the DCDC specimens would show at least 4.3 fold delayed crack initiation time than conventional tensile fracture specimens under a constant loading speed. Using DCDC specimens, we were able to observe the in-situ crack propagation process in a particle reinforced transparent polymer composite. Our results confirmed that the DCDC specimen would be a good candidate for the in-situ observation of the behavior of particle reinforced composites with slow crack velocity, such as the self-healing process of micro-particle reinforced composites.

A method to evaluate interfacial fracture energy on a fibre/matrix interface

A double cleavage drilled compression (DCDC) specimen was analysed using the boundary element method. The DCDC specimen of FRP composites was proposed and used to evaluate the interfacial behaviour and fracture energy in model composites of carbon fibre reinforced polymer (CFRP). As a result, it was confirmed that the DCDC specimen had the mode I stress distribution for the hole offsetting displacement of b = 0, in which the specimen configuration was symmetrical, while it had the mixed-mode stress distribution for b = 0. The approach of calculating the interfacial fracture energy was established using both the analysis and experiments. Furthermore, the bridging fibre DCDC specimen was proposed and the effect of bridging fibres on the loading phase was made clear. It was shown that the DCDC test was a useful method to evaluate the interfacial behaviour of fibre/matrix in composites.

Crack path instabilities in DCDC experiments in the low speed regime

We studied the low speed fracture regime (10 −4–10 −9 m s −1) in different glassy materials (soda-lime glass, glass ceramics) with variable but controlled length scale of heterogeneity. The chosen mechanical system enabled us to work in pure mode I (tensile) and at a fixed load on double cleavage drilled compression specimen. The internal residual stresses of studied samples were carefully relaxed by appropriate thermal treatment. By means of optical and atomic force microscopy techniques fracture surfaces have been examined. We have shown for the first time that the crack front line underwent an out-of-plane oscillating behavior as a result of a reproducible sequence of instabilities. The wavelength of such a phenomenon is in the micrometer range and its amplitude in the nanometer range. These features were observed for different glassy materials providing that a typical length scale characterizing internal heterogeneities was lower than a threshold limit estimated to few nanometers. This effect is the first clear experimental evidence of crack path instabilities in the low speed regime in a uniaxial loading experiment. This phenomenon has been interpreted by referring to the stability criterion for a straight crack propagation as presented by Adda-Bedia et al. [Phys. Rev. Lett. 76 (1996) 1497].

Limits of crack growth stability in the double cleavage drilled compression specimen

A theoretical investigation of the double cleavage drilled compression specimen was undertaken to define the limits of stable crack growth for a range of geometries and fracture toughnesses typically used in fracture testing of brittle materials. Two-dimensional large displacement solutions for the mode I stress intensity factor were derived using energy methods. Comparisons with finite element results indicate that these models maintain a high level of accuracy well past the onset of unstable crack growth. Crack growth stability was assessed by differentiating the semi-analytical solutions and assembling the results in the form of design curves.

Further analysis of the DCDC specimen with an offset hole

The results of He et al. (1995) for the Double Cleavage Drilled Compression (DCDC) specimen are extended to cover the case where both the hole and crack are offset from the centerline of the specimen. The effect of the thickness of an adhesive layer on the value of the energy release is also investigated. The applicability of the results to experimental studies is presented.

Crack growth behavior of zinc tellurite glass with or without sodium oxide

The crack growth behavior was investigated for zinc tellurite glasses with or without sodium oxide by using a small-size double cleavage drilled compression (DCDC) specimen, which was a rectangular bar with a small hole in the middle. The sample dimensions used were about a half or less than those of the previous studies, and comparable with those of JIS specimen for flexural strength testing. The validity of applying such a small specimen for test was examined on a commercial soda-lime silicate glass, and it was found feasible to obtain the data and to discuss crack growth behavior of glass. By using this small-size DCDC specimen, K I− v curves for tellurite glasses were successfully obtained for the first time. It was found that K I− v curves showed three characteristic regions similar to silicate glasses, but they shifted considerably toward the low K I side, reflecting much weaker bond-strength of tellurite glass than silicate glass. The fatigue parameter for tellurite glass was much larger than that for commercial silicate glass. This large fatigue parameter of tellurite glass was considered to result from a relatively small contribution of stress corrosion reaction to the subcritical crack growth because of the narrow distribution of bond-strength caused by the lack of ring structures in tellurite glass.

Crack Growth in the High Crack Velocity Region for Binary Sodium Silicate Glasses.

The crack growth behavior in the high crack velocity region (region III) for binary sodium silicate glasses was investigated by using a DCDC (double cleavage drilled compression) specimen under compressive stress. For 15mol% Na2O glass, despite the anomalous characteristic of the bulk modulus, subcritical crack growth in region III was detected. The slope of stress intensity factor (KI)-crack velocity (v) curve for silicate glass depended on the number of non-bridging oxygen per SiO4 tetrahedron rather than on the alkali content in the glass. This compositional dependence of the slope of KI-v curve for silicate glasses could not be explained in terms of thermally activated crack growth process where the crack-tip shape would vary with the pressure derivative of bulk modulus. The smaller KI-v slope and the higher KIC value of 35mol% Na2O glass may be related to the structural change from a three-dimensional network to a two-dimensional network because of the introduction of many non-bridging oxygens into the silica network.

Moisture-assisted crack growth at epoxy–glass interfaces

The double cleavage drilled compression (DCDC) test was used to measure the critical energy release rate, moisture-assisted crack growth, and fatigue threshold for epoxy–glass interfaces bonded with and without a silane coupling agent. The DCDC specimen consists of two glass beams (either soda-lime or fused silica) bonded together with an epoxy adhesive. A through-the-thickness hole is drilled in the centre of the specimen. In the DCDC test compressive loading causes tensile stresses to develop at the poles of the drilled hole. Cracks then nucleate in the epoxy–glass interface, extend from the poles, and propagate axially along the interface in primarily mode I loading. The resistance to moisture-assisted crack growth at untreated epoxy–glass interfaces is significantly less than that in monolithic glass specimens. However, the resistance to moisture-assisted crack growth at silane bonded epoxy–glass interfaces can be comparable with or greater than that in monolithic glass. Silane bonding of epoxy to glass is more effective with fused silica than soda-lime glass, with the fatigue limit of silane bonded epoxy–fused silica interfaces being about 2.5 times greater than that for silane bonded epoxy–soda-lime glass. These results are discussed in terms of possible interfacial crack growth mechanisms. © 1998 Kluwer Academic Publishers

Evaluation of Interfacial Behavior of FRP Composites in DCDC Test. Fracture of Fiber/Matrix Interface in Mixed-Mode.

A double cleavage drilled compression (DCDC) specimen with fiber/matrix interface has been proposed and analyzed in mixed-mode using the boundary element method (BEM). At the same time, the experiments on this DCDC specimen were conducted for CFRP composites in order to examine the crack propagating behavior and calculate the interfacial fracture energy at the fiber/matrix interface. It was confirmed that the DCDC specimen with the hole offset from the mid plane has a mixed-mode stress distribution, and the effect of the mode II on interfacial fracture energy increases with the offset value. The DCDC specimen in mode I with bridge fiber at the mid plane is also analyzed. It is found that the transition from the mode I to the mixed-mode occurs when the bridge fiber with angle to the mid plane exists. It was shown that the DCDC test is a useful method for evaluating the interfacial behavior of fiber reinforced plastic materials. However, both experimental and analytical approaches are needed to achicve a quantitative evaluation of the fiber/matrix interface.

Evaluation of Interfacial Behavior of FRP Composites in DCDC Test. Fracture of Fiber/Matrix Interface in Mode I.

A double cleavage drilled compression (DCDC) specimen with fiber/matrix interface has been proposed and analyzed in mixed-mode using the boundary element method (BEM). At the same time, the experiments on this DCDC specimen were conducted for CFRP composites in order to examine the crack propagating behavior and calculate the interfacial fracture energy at the fiber/matrix interface. It was confirmed that the DCDC specimen with the hole offset from the mid plane has a mixed-mode stress distribution, and the effect of the mode II on interfacial fracture energy increases with the offset value. The DCDC specimen in mode I with bridge fiber at the mid plane is also analyzed. It is found that the transition from the mode I to the mixed-mode occurs when the bridge fiber with angle to the mid plane exists. It was shown that the DCDC test is a useful method for evaluating the interfacial behavior of fiber reinforced plastic materials. However, both experimental and analytical approaches are needed to achicve a quantitative evaluation of the fiber/matrix interface.

Room‐Temperature Cyclic Fatigue of Reaction‐Bonded Silicon Nitride Using the Double Cleavage Drilled Compression Specimen

The double cleavage drilled compression specimen was used to study the room‐temperature cyclic fatigue behavior of reaction‐bonded silicon nitride (RBSN). Fatigue results were compared with slow crack growth under static loading. The fatigue exponent for RBSN was found to be 40, although no slow crack growth occurred under static loading. The fatigue threshold for RBSN was as low as 0.5/Klc and dependent upon loading conditions. Crack growth behavior and electron microscopy provided evidence that the fatigue mechanism was due to asperity and debris wedging at the crack face.

Analysis of the double cleavage drilled compression specimen for interface fracture energy measurements over a range of mode mixities

The double cleavage drilled compression (DCDC) configuration has been analyzed using the finite element method. Mode I and mixed-mode configuration have been described and results presented for the energy release rate, the mixity angle and the crack opening displacement. The results have been expressed as simple analytical formulae having good accuracy. The application of the configuration to interface fracture measurements has been described.

Stress intensity calibration for the double cleavage drilled compression specimen

The normalized crack tip stress intensity for the double cleavage drilled compression (DCDC) specimen is characterized as a function of crack length by both experimental and numerical means. The experimental calibration is based on measurements of the critical applied load to produce crack growth in silica glass in an ultra high vacuum environment. Results from the experimental calibration are in good agreement (within 10%) with a finite element analysis of the crack tip stress intensity ( K I ) using the ABACUS code. The results indicate that K I is strongly dependent upon the ratio of the hole size to the sample width used in the DCDC sample geometry even for cracks which are long with respect to the hole diameter.

Theoretical analysis of the double cleavage drilled compression specimen

A theoretical analysis of stress intensity factors and crack opening displacements for the double cleavage drilled compression specimen (DCDC) is presented. This specimen exploits a well known fact that the stress field around a circular hole in a plate subjected to uniaxial stress reverses sign at points on the hole which are parallel to the applied stress. Under uniaxial compression, tensile stresses exist at the edge of the hole and this tensile stress propagates a crack in the DCDC specimen. Because this tensile region is very localized, catastrophic crack growth cannot occur and it is not necessary to groove the specimen to promote straight crack growth. The controlled crack growth possible with this specimen should make it possible to examine fracture mechanisms in detail. The simplicity of this test specimen also makes it an ideal candidate for studying environmental effects on fracture.