Tapered Double Cantilever Beam Specimens Research Articles

The use of tapered double cantilever beam (TDCB) in investigating fracture properties of particles modified epoxy

This study compares fracture energy of an epoxy polymer from the addition of different wt% of nanoparticles, for both experimental and FEA modelling studies. Silica and core–shell rubber (CSR) particles, and the hybrid of both (from 0.5 wt% to the maximum concentration of 25.4 wt%) are used. An increase in fracture energy was found in the CSR and hybrid specimens, but clustering of particles caused a reduction in the mechanical properties when the concentration of particles was high. As there was interfacial failure found with some tapered double cantilever beam (TDCB) specimens. Therefore, the fracture energies measured with TDCB specimens are also compared with simulation results using the finite element analysis software ‘Abaqus’. These results provided further information for the next stage of investigations in fracture properties of particles modified epoxy.

A Study on the Fatigue Fracture for Out-Plane Shear According to TDCB Slope Angle by Using UD CFRP

Weight lightening in transport machines satisfies both internal combustion engines’ performance and efficiency and emission reduction technologies. Weight lightening is a part of ongoing research to increase the range of electric power sources. Carbon fiber reinforced plastics (CFRP) is a lightweight material with the highest specific strength. However, CFRP is used as a metal and dissimilar material in the part because it is vulnerable to the manufacturing process due to by the cracks in internal fiber structures. In this study, the design dimensioning, mechanical strength characteristics, and durability characteristics of tapered double cantilever beam (TDCB) with mode III (Out-plane shear) load according to slope angle using UD CFRP were determined through the adhesive peeling static and fatigue test. Mode III (Out-plane Shear) adhesive peeling static and fatigue tests showed that TDCB specimen has excellent strength and durability of 8° as a result of the mode III adhesive peeling static and fatigue test. The standards and methods used in this study were conducted in accordance with the British industrial standards (BS 7991) and ISO international standards (ISO 11343).

Toughening effect of nanocomposite-wall microcapsules on the fracture behavior of epoxy

In this research the reinforcing effect of nanocomposite-wall microcapsules on the fracture toughness and fracture energy of epoxy under mode I was studied. The fracture specimens with the geometry of localized tapered double cantilever beam (TDCB) were used to take the advantage of crack length independent-measurement in determining the fracture properties. The crack length investigations were performed experimentally and numerically to extract the calibration parameters and also evaluate the optimal crack length of TDCB specimens. Three types of microcapsules including hollow microcapsule (CH), ethyl phenylacetate core microcapsule (CEPA) and NH2-CNT reinforced-wall microcapsule (CCNT) were synthesized and used as reinforcements. The scanning electron microscopy study of synthesized microcapsules proved the successful presence of CNTs in the shell and on the wall of CCNT microcapsules. The hollow capsule-loaded epoxy composite exhibited enhanced fracture properties as compared to the neat epoxy. Moreover, the SEM study of fracture surface of CH reinforced specimen revealed a characteristic crack tail toughening mechanism. The CEPA microcapsule decreased fracture properties of neat epoxy. The maximum improvement of fracture properties belonged to the specimen containing the CCNT microcapsules. It was observed that the composite-wall microcapsule was able to increase the fracture toughness and fracture energy of neat epoxy by 59% and 165%, respectively, due to the developments of considerable out-of-plane fracture and large plastic deformation.

Fracture behavior of adhesive interface at TDCB aluminum foam specimen with the type of Mode III

In this study, the fracture property is investigated with the configuration of tapered double cantilever beam different from that of the existing double cantilever beam. Aluminum TDCB (Tapered Double Cantilever Beam) specimens of mode III-type are bonded by an adhesive. The specimens had thicknesses as a variable which were 35 mm, 45 mm, and 55 mm, respectively. In the case of the specimen with a thickness of 35 mm, the maximum reaction force was shown to be about 0.4 kN when the forced displacement had progressed by about 8 mm, while the maximum reaction force of about 0.45 kN occurred in case of the specimen with a thickness of 45 mm when the forced displacement proceeded by about 7 mm, and the maximum reaction force of about 0.54kN occurred in case of the specimen with a thickness of 55mm when the forced displacement proceeded by about 7 mm. In addition, the static fracture analysis was performed for its verification by using the finite element analysis of ANSYS program, where it was affirmed that the experimental results and the simulation analysis results were shown to be similar. Based on this observation, it is considered that the simulation analysis data could be applied to the bonded interfaces of actual porous materials.

Cohesive fracture of elastically heterogeneous materials: An integrative modeling and experimental study

A combined modeling and experimental effort is made in this work to examine the cohesive fracture mechanisms of heterogeneous elastic solids. A two-phase laminated composite, which mimics the key microstructural features of many tough engineering and biological materials, is selected as a model material system. Theoretical and finite element analyses with cohesive zone modeling are performed to study the effective fracture resistance of the heterogeneous material associated with unstable crack propagation and arrest. A crack-tip-position controlled algorithm is implemented in the finite element analysis to overcome the inherent instability issues resulting from crack pinning and depinning at local heterogeneities. Systematic parametric studies are carried out to investigate the effects of various material and geometrical parameters, including the modulus mismatch ratio, phase volume fraction, cohesive zone size, and cohesive law shape. Concurrently, a novel stereolithography-based three-dimensional (3D) printing system is developed and used for fabricating heterogeneous test specimens with well-controlled structural and material properties. Fracture testing of the specimens is performed using the tapered double-cantilever beam (TDCB) test method. With optimal material and geometrical parameters, heterogeneous TDCB specimens are shown to exhibit enhanced effective fracture energy and effective fracture toughness than their homogeneous counterparts, which is in good agreement with the modeling predictions. The integrative computational and experimental study presented here provides a fundamental mechanistic understanding of the fracture mechanisms in brittle heterogeneous materials and sheds light on the rational design of tough materials through patterned heterogeneities.

A study on fatigue fracture at double and tapered cantilever beam specimens bonded with aluminum foams

Abstract In this study, the models of simple double cantilever beam (DCB) and tapered double cantilever beam (TDCB) were designed to analyze the fracture behavior of the aluminum foam. The fracture behaviors of composite materials exhibit similar trends. The energy release rate increases as the crack length increases and the specimen height decreases. The bonding force influences the adhesive joints of structure. The DCB and TDCB model can be applied generally to the structure with complex configuration. An aluminum foam model has been constructed by using the configuration of DCB and TDCB models in this study. This paper studies the fracture characteristics of specimens due to two kinds of configurations by comparing with the experimental results of DCB and TDCB specimens for mode 1. This study aims to apply fracture toughness to the design of adhesive joints.

In-depth numerical analysis of the TDCB specimen for characterization of self-healing polymers

The Tapered Double Cantilever Beam (TDCB) is the common specimen to study self-healing thermosetting polymers. While this geometry allows characterising the mode I fracture toughness without taking into account the crack length, the experiments show an important dispersion and unstable behaviour that must be taken into account to obtain accurate results. In this paper, finite element simulations have been used to understand the experimental behaviour. Static simulations with a stationary crack give the local stresses and the stress intensity factors at the crack tip when the TDCB is under load. In addition, the eXtended Finite Element Method (XFEM) has been used to make quasi-static crack propagation simulations. The results indicate that the crack tip has a curved profile during the propagation, advancing more at the edges than at the centre. The crack propagation begins when the applied load reaches a critical value. The unstable crack propagation noted in the experiments can be reproduced by introducing an unstable behaviour in the simulations. Finally, the sensitivity of the critical load has been studied as a function of the friction between pin and hole, tolerance of geometrical dimensions, and cracks out of the symmetric plane. The results can partially explain the dispersion of the experimental data.

High-strain-rate fracture of adhesively bonded composite joints in DCB and TDCB specimens

Double-cantilever beam (DCB) and tapered double-cantilever beam (TDCB) specimens are the test configurations most commonly used to measure the fracture toughness of composites and adhesive joints. Strain rates of 1 to 18.47 m/s were applied to the test specimens via high-speed hydraulic test equipment. Because the fracture occurs through the adhesively bonded joints and the cracks grow rapidly, the crack length and beam displacement were recorded by a high-speed camera. An energy range from 0 to 10 J was often observed in the high-strain-rate fracture experiments for nonlinear plastic behavior of the dynamically loaded adhesively bonded DCB and TDCB specimens. The range of energy release rates (fracture energy) for TDCB specimen was 2 to 3 times higher than that of a DCB specimen for all high strain rates. The fracture energy of automotive adhesive joints can be estimated using the experimental results in this study for the fracture toughness (GIC) under high rates of loading. The crack grows as the applied fracture energy exceeds the value of the critical energy release rate (GIC) at the crack tip. The energy release rate was calculated using the fracture mechanics formula. The key fracture mechanics parameter, the fracture energy GIC, was ascertained as a function of the test rate and can be used to assess and model the overall joint performance.

Effect of specimen geometry on fracture toughness measurement of plasma-sprayed ceramic coatings by the tapered double cantilever beam approach

The measurement of fracture toughness of plasma-sprayed ceramic coatings is usually performed using a standard double cantilever beam approach. The design of specimen geometry using a tapered double cantilever beam (TDCB) approach makes the compliance of specimens be linearly proportional to crack length. Fracture toughness in terms of critical strain energy release rate can be obtained by measuring fracture load only. Three varieties of the TDCB specimens are used to examine the effect of the geometry and size of specimens on the results. These are simple TDCB, modified and long TDCBs. Plasma-sprayed Al 2O 3 coatings are used in test. It was found that linearly proportional relations are experimentally obtained between the compliance of the specimen and crack length for all three varieties of the TDCB samples. Fracture toughness of plasma-sprayed Al 2O 3 coating is independent on the geometry of the test piece used in the study. The TDCB approach is a simple and reliable approach to measure fracture toughness of thermal spray coatings without the measurement of crack length.

Tapered beam on elastic foundation model for compliance rate change of TDCB specimen

A modified beam theory is developed to predict compliance rate change of tapered double cantilever beam (TDCB) specimens for mode-I fracture of hybrid interface bonds, such as polymer composites bonded to wood. The analytical model treats the uncracked region of the specimen as a tapered beam on generalized elastic foundation (TBEF), and the effect of crack tip deformation is incorporated in the formulation. A closed-form solution is obtained to compute the compliance and compliance vs. crack length rate change. The present TBEF model is verified with finite element analyses and experimental calibration data of compliance for wood–wood and wood–composite bonded interfaces. The compliance rate change can be used with experimental critical fracture loads to determine the respective critical strain energy release rates or fracture toughness of interface bonds. The present analytical model, which accounts for the crack tip deformation, can be efficiently and accurately used for compliance and compliance rate-change predictions of TDCB specimens and reduce the experimental calibration effort that is often necessary in fracture studies. Moreover, the constant compliance rate change obtained for linear-slope TDCB specimens can be applied with confidence in mode-I fracture tests of hybrid material interface bonds.

Compliance rate change of tapered double cantilever beam specimen with hybrid interface bonds

This paper presents a combined numerical and experimental study of compliance rate change of Tapered Double Cantilever Beam (TDCB) specimens for Mode-I fracture of hybrid interface bonds. The easily machinable TDCB specimen, which is designed to achieve a constant rate of compliance change with respect to crack length, is developed for Mode-I fracture tests of hybrid material bonded interfaces, such as wood bonded to fiber-reinforced plastic (FRP) composite. The linearity of compliance crack-length relationship of the specimen is verified by both Rayleigh–Ritz method and finite element analysis. An experimental compliance calibration program for specimens with wood–wood and FRP–FRP bonded interfaces is carried out, and a constant rate change of compliance with respect to crack length is obtained for a specific range of crack length. Fracture tests are further performed using TDCB specimens for wood–wood and wood–FRP bonded interfaces to determine the critical loads for crack initiation and crack arrest, and using the constant compliance rate change of the specimens determined by experiment or analysis, the respective critical strain energy release rates, or fracture energies, are obtained. This study indicates that the constant compliance rate change obtained from experiment or finite element analysis for linear-slope TDCB specimens can be used with confidence for fracture studies of hybrid material interface bonds.

Dynamic crack growth in TDCB specimens

Dynamic crack propagation in tapered double cantilever beam (TDCB) specimens is analysed via beam theory and the finite element method. Steady state and transient solutions of the energy release rate G are given for various load conditions. Finite element analysis is performed to obtain the dynamic G at given crack speed or the crack history for a given fracture toughness. The stress wave effects on the dynamic G are discussed. The beam solutions are compared with the finite element results and some experimental phenomena are explained.

Hydrothermal Stability of Aluminum/Epoxy Adhesive Bonds

Abstract The effect of silane primers on the failure properties of aluminum/epoxy tapered double cantilever beam (TDCB) specimens was determined. TDCB specimens that were tested in air using increasing loads always failed by propagation of cracks along the center of the bondline at Glc values between 1.58 and 1.80 × 105 mJ/m2 whether primers were used or not. However, γ-aminopropyltriethoxysilane (γ-APS) primers had a significant effect on the time to failure of TDCB specimens subjected to static loads in water at 60°C. The time to failure was always increased when the beams were pretreated with dilute aqueous solutions of γ-APS. The pH at which the primers were applied did not affect the failure charactersitics of the beams but heat treating the primer films before bonding did. The longest times to failure were always obtained when the primer films were dried in air at 100°C for about ten minutes. Shorter or longer drying times always resulted in lower times to failure. Increases in time to failure obtai...

Relationship between fracture toughness and acoustic emission during cleavage failure in adhesive joints

Fracture toughness in mode I was determined for wood bonded with various adhesive systems. Tapered double-cantilever beam (TDCB) specimens were used, with attached transducer connected to instrumentation for monitoring acoustic emission. Adhesives used fro bonding the TDCB specimens included urea-formaldehyde resin, phenol-resorcinol resin, and emulsion polymer isocyanate, among others. Test parameters measured included critical load for cleavage fracture and number of events (stress waves) emitted, from which fracture toughness and cumulative count of acoustic emission were computed. It was found that there was a well defined, linear relation between fracture toughness and cumulative counts of acoustic emission per fracture area. The fracture toughness values of systems containing polyvinyl acetate and of epoxy resin were larger than those of thermosetting resins such as urea-or phenol formaldehyde. The high fracture toughness imparted by polyvinyl acetate was attributed to viscous movement of linear molecular chain segments, as compared with the more brittle behavior of the crosslinked molecular structure of such resins as ureaformaldehyde.

Further Dynamic Finite Element Analysis of the Tapered DCB Specimen

A dynamic finite element code was used to compute the dynamic stress intensity factors and crack arrest stress intensity factor which are related to the crack run-arrest response in a tapered double cantilever beam (DCB) specimen machined from A533B steel. Measured crack velocities of a fracturing tapered DCB specimen were used to prescribe a crack motion under both fixed grip and variable loading conditions at the two loading pins. Numerically and experimentally determined dynamic strains were compared at three locations on the fracturing tapered DCB specimen. This comparative study showed that the fixed grip condition modeled the actual dynamic state well and that the crack arrest stress intensity factor, KIa, computed on the bases of fixed grip and variable loading conditions differed by a factor of approximately 0.6.