Interfacial Energy Release Rate Research Articles

Measurement of the interfacial energy release rate (ERR) and cohesive law parameters of polyvinyl butyral laminated glass using a novel beam-type test specimen

The polyvinyl butyral (PVB) laminated glass (LG) structures are widely used in architectural and automotive sectors. Determination of the interfacial fracture energy (i.e. G) between the PVB layer and glass is one of the most vital procedures for ensuring the structural safety and fracture resistance of these kinds of components. The present study investigates the adhesion characteristics between glass and PVB interface in a LG composite structure. A new simple test fixture is introduced to measure the mixed-mode fracture energy from pure mode I (i.e. GI) to pure mode II (i.e. GII). By making use of the concept of Equivalent material Concept (EMC), linear elastic fracture mechanics (LEFM) formulations together with finite element (FE) analysis can be used to compute the compliance parameter of the system and pure modes I/II fracture energies. Besides, the interaction of cohesive forces between the PVB layer and glass are simulated by using a FE method based on a bi-linear cohesive zone model (CZM) technique. In this regard, the cohesive law parameters are computed for mode I and mode II in an iterative process. Then, the obtained pure mode cohesive law parameters are utilized to predict the mixed-mode load–displacement diagrams. The obtained results demonstrate the satisfactory accuracy of the cohesive law parameters and fracture energies in predicting the mixed-mode loading results across four different loading rates (i.e. LR = 2, 5, 10, and 15 mm/min).

Ice Adhesion Properties on Micropillared Superhydrophobic Surfaces.

In this work, we investigate the freezing behavior and ice adhesion properties of sessile drops on micropillared superhydrophobic surfaces (SHSs) with various sizes, which are of practical importance for anti/deicing. First of all, it is demonstrated that the recalescence is related only to the supercooling degree of drops but not to the geometrical parameters of micropillars. The freezing time of sessile drops first increases and then decreases with the area fraction of the SHSs, which demonstrates the nonmonotonic dependence of the icing time on the area fraction. Moreover, the influence of the geometrical parameters of the micropillars on the ice adhesion is discussed. With the decrease of the substrate temperature, the wetting state of the adhesive ice can be transformed from the Cassie ice to the Wenzel ice. For the Cassie ice, the adhesive force is proportional to the area fraction of the SHSs. Interestingly, experimental results show that there exist two interfacial debonding modes of the Wenzel ice: translational debonding and rotational debonding. Furthermore, it is found that the rotational debonding mode contributes to a much lower adhesive force between the ice and the micropillared surface compared to that of the translational debonding mode. By analyzing the critical interfacial energy release rate of the two modes, we deduce the threshold between the two modes, which is quantified as the geometrical parameters of the micropillars. In addition, quantitative relations between the geometrical parameters and the adhesion strengths of the two modes are also obtained. We envision that this work would shed new light on the design optimization of anti/deicing materials.

Mechanical Characterisation and Cohesive Law Calibration for a Nitrocellulose Based–Cyclotetramethylene Tetranitramine (HMX) Polymer Bonded Explosive

BackgroundMechanical characterisation of polymer bonded explosives (PBXs) is crucial for their safe handling during storage and transportation. At temperatures higher than the binder's glass transition temperature, fracture is caused predominantly by interface debonding between the binder and explosive crystals. Interfacial friction between debonded crystals can lead to accidental detonation of the PBX material, even under a very small external load. Cohesive zone laws can describe this interfacial debonding.ObjectiveThis study aims to experimentally calibrate the interfacial cohesive zone parameters of a nitrocellulose based–cyclotetramethylene tetranitramine (HMX) PBX, a particulate composite with an 88% volume fraction of crystals.MethodsCompact tension fracture tests, coupled with Digital Image Correlation (DIC) were used to capture the strain fields around the crack tip. The experimental data were used in conjunction with an extended Mori–Tanaka method considering the effect of interfacial debonding.ResultsThe cohesive zone parameters were successfully calibrated and were found to be crosshead rate independent. The values of the critical traction {sigma }_{int}^{max} and interfacial energy release rate, {gamma }_{if}, dropped significantly with increasing temperature. The experimental method followed in this study is generic, and it can be employed to extract the cohesive zone parameters characterising the interface behaviour between the filler and matrix in other particulate filled, polymer composite materials.ConclusionsCohesive zone properties can be experimentally determined to provide inputs in micromechanical simulations linking the microstructure of the PBX composite to its macroscopic response as well as enabling the estimation of hot spot formation at debonded crystal interfaces.

Infusible thermoplastic resin based sandwich structures for wind blade applications and the influence of scrim on facesheet to core interface debonding

Infusible thermoplastic Elium® family of resins from Arkema have garnered much attention in recent years as a possible replacement for thermoset resins in laminate and sandwich composite manufacturing for wind blade applications due to its ease of recyclability and the ability to utilize existing manufacturing processes without imposing complicated variations. However, physical and mechanical properties of the proposed Elium® based thermoplastic composites must be comparable to existing epoxy (thermoset) based composites using manufacturing processes relevant for large wind turbine blades. A 13-meter-long demonstration blade was manufactured for that purpose and sandwich samples were obtained from that project for a detailed study. This paper details three-point flexural properties of unidirectional E-glass fiber reinforced acrylic and epoxy based sandwich panels with identical balsa wood core materials. In addition, to evaluate the relative merit considering debond failure mode, the interfacial critical strain energy release rate, predominantly in mode-1, was compared via single cantilever beam testing. In sandwich composites constructed with balsa wood core material, resin uptake by the balsa core is traditionally impeded via the insertion of a scrim material at the facesheet to core interface. Results revealed that inclusion of scrim mesh layer at the facesheet to core interface reduced flexural properties and strain energy release rates in panels infused with acrylic resin but did not significantly reduce these properties in epoxy infused facesheets.

Measurement of the interfacial strain energy release rate of adhesively bonded structures with metallic substrates before and after water ageing

The aim of the presented work is to propagate cracks at interfaces between adhesive joints and metallic substrates and to measure the Strain Energy Release Rate (SERR). In order to propagate at a specific interface and not cohesively, a specific specimen was developed, based on a modification of the Tapered Double Cantilever Beam (TDCB) specimen. In particular, the dimensions of one substrate were reduced to create an asymmetry in the specimen and drive the propagation path towards one interface. The authors present experimental results showing repetitive interfacial failures and a procedure to evaluate the SERR. The non-linear behaviour responsible of non-linear deformation in the substrate was taken into account in the calculations of the SERR. Through a numerical inverse method using Finite Element Analysis (FEA) and Cohezive Zone Modelling (CZM), the SERR was calculated for an epoxy based structural adhesive at the interface with a stainless-steel substrate. Then, the procedure was carried out to measure the interfacial SERR after different ageing times.

Evaluation of the delamination performance of polyvinyl-butyral laminated glass by through-cracked tensile tests

The interfacial adhesion between the interlayer and glass plays a vital role in determining the safety and post-fracture behavior of PVB-laminated glass. To get a better understanding of the delamination behavior of PVB-laminated glass, a series of through-cracked tensile (TCT) tests were carried out. Influences of different PVB adhesion grades (TROSIFOL® BG R15 and BG R20), loading rates (3 mm/min and 300 mm/min), and interlayer thicknesses (0.76 mm, 1.52 mm, and 2.28 mm) were considered in the tests. Digital image correlation (DIC) technology was adopted to record the delamination process. The delamination length, strain distribution on the PVB interlayer as well as delamination angle, were obtained through DIC analysis. Based on the test results, three typical delamination modes, i.e., unstable delamination, stable delamination, and restricted delamination, were observed. The delamination mode is strongly dependent on the adhesion grade and loading rate. Furthermore, to evaluate the interfacial adhesion, energy release rates were calculated based on an analytical approach. The adhesion grade dominates the delamination performance of the PVB-laminated glass. The delamination length of BG R15-laminated glass is much larger than that of BG R20-laminated glass due to lower interfacial energy release rate and hence exhibits better deformability. With the increase of the loading rate, the energy release rate increases for both BG R15 and BG R20 interlayers. The influence of PVB thickness on the interfacial adhesion was insignificant. For the first time, the delamination angle was identified from DIC results, and the results were used to determine the interfacial fracture mode. The results from this study provide more detailed data on the PVB-glass interfacial adhesion properties and a reference for the post-fracture analysis of PVB-laminated glass.

Fatigue behavior of notched steel beams strengthened by a prestressed CFRP plate subjected to wetting/drying cycles

Prestressed carbon fiber reinforced polymer (CFRP) strengthening is effective in suppressing crack propagation of steel beams. However, the fatigue behavior of notched steel beams with prestressed CFRP under a hygrothermal environment is not fully understood. Generally, notch machining on the steel beam is an ordinary method to simulate a fatigue defect for laboratory tests. In this study, the interfacial energy release rate at the notch location was first derived for strengthened steel beams. The theoretical results show that the interfacial energy release rate can be significantly reduced by prestressed CFRP strengthening, contributing to improving the interfacial fatigue performance. In addition, notched steel beams strengthened by prestressed CFRP (with a prestress level of 25% of tensile strength of CFRP plate) were exposed to wetting/drying cycles (WDCs) and then tested under fatigue loading. The experimental results show that prestressed CFRP strengthening increases the fatigue resistance of interfacial debonding initiation and failure 3.47 times and 7.83 times, respectively, which agrees with the tendency revealed by the theoretical results. In contrast, WDC exposure reduced the fatigue lives of interfacial debonding initiation and failure by 34.6% and 27.2%, respectively. An S – N curve based on the maximum principal interfacial stress at the notch location was proposed to predict the tendency of fatigue life of debonding initiation for strengthened steel beams. Moreover, the tendency prediction for fatigue life of interfacial debonding development for the strengthened steel beams with/without WDC exposure was developed based on Paris’ law. • Theoretically reveals that the prestressed CFRP reduces the interfacial energy release rate. • Prestressed CFRP strengthening significantly improves interfacial fatigue life. • Hygrothermal exposure leads to a significant reduction of interfacial fatigue life.

Simulation of microscopic interface damage of ZrB2 based ceramics based on cohesive zone model

The interfacial energy release rate of ZrB2-based ceramics was obtained by combining the equivalent relationship between the stress intensity factor criterion in the local range of crack tip and the energy balance criterion. Cohesive zone model (CZM) is introduced to simulate the intergranular failure behavior. The damage parameters required by the CZM are calculated by Mori-Tanaka theory. Based on the microstructure of ZrB2-SiC ceramics, the representative volume element (RVE) is established and subjected to displacement load. Finally, the stress nephogram and damage evolution process of RVE are obtained and the process of stress change of matrix, particles, damage interface and undamaged interface of RVE with the load applied gradually are outputted.

An analytical solution for the inverted four-point bending test in orthotropic specimens

Analytical solutions are derived for interfacial energy release rate and mode mixity angle in the inverted four-point bending test. In the test, the loads applied in the classical four-point bending test are inverted so that the crack faces come into contact at the midspan and mode mixity with an important mode II component is produced. The contact forces are evaluated by employing a beam model and imposing that the two delaminated arms undergo the same deflection at the contact point. Friction is accounted for within an approximate Coulomb model. Both Timoshenko and Euler-Bernoulli beam theories are applied and local 2D effects due to near tip deformations are introduced through suitable analytically derived crack tip root rotations and displacements. The results are verified by comparison with finite element results. The model accurately estimates energy release rate and mode mixity angle in orthotropic specimens, also for short/intermediate delaminations, and defines the minimum length of the crack ensuring a steady state propagation under a constant value of energy release rate and mode mixity. Steady state propagation under different mode mixity conditions is demonstrated by varying the relative thickness of the delaminated arms.

Investigation into the evolution of interface fracture toughness of thermal barrier coatings with thermal exposure treatment by wedge indentation

Abstract

Simulated and experimental demonstrations of interfacial adhesive strength for released layer utilized in flexible electronics

Interfacial adhesive strength is an important characteristic considered in multilayered active-matrix organic light-emitting diode (AMOLED) architecture as it has an impact on the mechanical reliability issue generated from complicated organic/inorganic hybrid lamination and final debonding procedure. Thus, an appropriate released layer design is needed to manage the capability and reliability of the encapsulated AMOLED structure de-bonded from the temporary carrier. Accordingly, this research utilizes the plasma-assisted surface modification to improve the interfacial adhesive strength of the polyimide (PI)/debonding layer (DBL) during mechanical debonding. In addition, a fracture-based finite element model of peeling testing architecture is constructed to analyze the adhesive behavior of the PI/DBL interface via the utilization of the modified virtual crack closure technique. The analytic results indicate that the suitable plasma-assisted surface modification significantly increased the nitrogen concentration and generated the high dissociation energy N–O bonds among the bonded interface between the PI/DBL thin films. The opening mode-fractured energy also takes the dominance proportion in the entire peeling load-induced interfacial energy release rate. The application of plasma-assisted surface modification enhanced the delamination resistance of the concerned interface and maintained the structural stability during the lamination and related release of a whole flexible AMOLED architecture.

Mixed mode testing of a multi-directional woven laminate

Mixed-mode fracture toughness tests were carried out on a multi-directional laminate making use of a Brazilian disk specimen. The composite laminate consisted of plain, balanced woven plies with tows in the $$0^{\circ }/90^{\circ }$$ -directions and the $$+45^{\circ }/-45^{\circ }$$ -directions. The delamination was placed between two of these plies by means of a polytetrafluoroethylene (PTFE) film. Tests at various loading angles were performed in order to obtain a wide range of mode mixities. Each ply was homogenized by means of a micro-mechanical model to obtain its effective properties. The specimens were analyzed by means of the finite element method. An interaction energy or M-integral was extended for this interface to obtain the stress intensity factors. The latter were used to determine the critical interface energy release rate and two phase angles. Employing this information, a three-dimensional failure criterion proposed elsewhere was presented. The criterion may be used to predict failure of a composite structure containing a delamination along the interface and material studied here.

A simple 3-point flexural method for measuring fracture toughness of the dental porcelain to zirconia bond and other brittle bimaterial interfaces

PurposePorcelain fused to zirconia prostheses are widely used, but porcelain chipping, fracture, spalling and delamination are common clinical problems. Conventional bond strength testing is inherently unsuited for studying interfacial failure by cracking in brittle materials. Instead, fracture toughness is a more meaningful parameter because it can assess the robustness of the interface when subjected to loading, but fracture mechanics approaches have only rarely been used. Our purpose was to develop a novel, simple, 3-point flexural methodology and mathematical analysis to measure the fracture toughness of the porcelain to zirconia interface. MethodsEquations were derived to estimate the fracture toughness of the bond by computing the interfacial energy release rate for a novel simple 3-point flexural test model. The test was validated using two different configurations of layered zirconia/porcelain beams (n = 10), approximating the dimensions of a fixed dental prosthesis, fabricated from a tetragonal polycrystalline zirconium dioxide partially stabilized with yttria and a feldspathic dental porcelain. ResultsCracking along the bimaterial interface was produced and measured as a discrete event. Fracture toughness means (standard deviations) computed from the measured energy release rate, for the porcelain to zirconia interface in two different specimen configurations were 7.9 (1.3) and 5.3 (1.6) J/m2. ConclusionsEquations were derived to measure interfacial fracture toughness of brittle materials using a novel simple 3-point flexural test method. The test was then validated; estimates for the fracture toughness for the porcelain to zirconia bond, overlapped with previously published data derived from more complex 4-point notched tests.

Mode II interfacial fracture characterization of foam core sandwich materials at elevated temperatures: the effects of frictional stresses between the crack edges

In recent years, composite sandwich material has been widely used in civil engineering due to its high strength to weight ratio, high stiffness to weight ratio and anti-corrosion ability. However, the existing research studies indicated that interfacial delamination between skins and core was a common failure mode for this kind of material, which seriously threatens the durability and safety of structures. Furthermore, up to now, there are no research studies investigating the effects of elevated temperature on the interfacial fracture and damage behavior of the sandwich material. To address the above questions, this paper investigated the effects of elevated temperature on mode II interfacial fracture response of foam core sandwich materials by adopting the end-notched flexure method. Test results showed that the loads and the strain energy release rate decreased under the same crack length as the temperature increased. In the meantime, the corresponding analytical model, considering the effect of frictional stresses between the crack edges, has been proposed to predict the interfacial strain energy release rate. The comparison of the analytical and experimental results revealed that the analytical model could accurately predict the strain energy release rate of mode II interfacial fracture of foam core sandwich materials at elevated temperatures.

Comparison of methods for determination of fracture toughness in a multi-directional CFRP laminate

Quasi-static tests were carried out on calibrated end loaded split (C-ELS) specimens to determine a critical initiation interface energy release rate or fracture toughness Gic. A multi-directional (MD) carbon fiber reinforced polymer (CFRP) laminate with a delamination between a unidirectional (UD) fabric ply with fibers oriented mainly in the 0°- direction and a plain balanced woven ply with tows oriented in the +45°/ - 45°- directions was considered. The Gic values from the non-precracked (NPC) specimens containing an artificial delamination were evaluated by means of an experimental compliance method (ECM), a beam theory (BT) method, as well as a two-dimensional finite element analysis (FEA) together with the area J-integral. In addition, the displacement extrapolation (DE) method and the virtual crack closure technique (VCCT) were used to determine the stress intensity factors Km (m = 1, 2) for each test. The stress intensity factors were normalized with a length scale L^ = 100 µm and used to calculate the phase angle ψ^. Finally, the obtained results were compared to critical initiation values which were obtained in a previous study from Brazilian disk (BD) tests for the same material and interface. The Gic value is a necessary property for predicting propagation of a delamination along the investigated interface. The aim of this paper is to examine the differences which occur as a result of using various methods to determine this value. Work is in progress to determine fracture resistance curves or R-curves. These curves relate the energy required for a delamination to propagate GR to the delamination extension Δa and may be used to predict the delamination resistance to propagation.

Analysis of Interface Fracture of Cold-Sprayed Coatings Due to Thermal Cycling

Driving mechanisms for the interface delamination of cold-sprayed chromium on a steel substrate subjected to cyclic thermal loading are studied by using thermomechanical analysis. First, the equilibrium stress states of the coating system due to residual stresses are determined for different coating thickness vales. This system is then subjected to periodic heating and cooling cycles. The potential of crack initiation and growth is simulated with and without embedded micro-cracks. The corresponding crack-driving forces are characterized using the interface stresses and energy release rate as a function of the thermal cycles. The effects of coating thickness, location of the embedded micro-cracks and initial residual stress on these driving forces are investigated systematically to demonstrate the risk of coating fracture and delamination.

Two- and Three-Dimensional Failure Criteria for Laminate Composites

Abstract Several two- and three-dimensional mixed-mode interface failure criteria are proposed for predicting delamination failure in multidirectional, laminate composites. The proposed criteria, based on the stress intensity factors K1, K2, and KIII, as well as the critical interface energy release rate Gic and phase angles ψ and ϕ, are examined using results obtained from Brazilian disk mixed-mode fracture toughness tests. Two material systems are considered. The first contains a delamination along an interface between a unidirectional fabric and a plain woven fabric. The second is composed of a plain woven fabric with fibers oriented in different directions in succeeding plies. The former was manufactured by means of a wet-layup and the latter is a prepreg. Finally, a statistical analysis is carried out to obtain a failure curve or surface with a 10% probability of unexpected failure and a 95% confidence. These curves or surfaces may be used to predict failure of structures containing these laminates and to assist in composite design.

Trans-scale characterization of interface fracture in peel test for metal film/ceramic substrate systems

In order to describe the interfacial fracture behaviors of the metal thin film with nano- or microscale thickness peeled on the ceramic substrate, a trans-scale mechanics model has been adopted. In the trans-scale mechanics model, both the strain gradient effect and surface/interface effect are considered. In addition, two fracture process models are used in present study, which are the cohesive zone model and the virtual internal bond model. Using the trans-scale mechanics theory and the interface models, the size effect of the interfacial separation strength between the metal thin films and the ceramic substrates is analyzed systematically by using the peel test. The results show that the fracture process zone size could be taken as the indicator of the trans-scale interface fracture characterization. The interface effect should be considered when the fracture process zone size is at the nanoscale, and the obtained interfacial separation strength is much higher than the conventional separation strength. The material length scale parameters of the metal films are determined by comparing the interfacial energy release rate predicted by the scale theories with the experimental results, which shows that the material length scale parameter could be regarded as the size of active plastic zone in the small scale yielding case during the peeling process.

Multi-directional composite laminates: fatigue delamination propagation in mode I—a comparison

Double cantilever beam (DCB) specimens composed of carbon fiber reinforced polymer laminate composites were tested. Two material systems were investigated. One consisted of plies from a woven prepreg alternating with tows in the $$0^{\circ }/90^{\circ }$$-directions and the $$+45^{\circ }/-45^{\circ }$$-directions. The second was fabricated by means of a wet-layup process with the same multi-directions as the prepreg. In addition, for the second material system, a unidirectional (UD) fabric ply was added. The delamination for this laminate was between the UD fabric and the woven ply with tows in the $$+45^{\circ }/-45^{\circ }$$-directions. Both fracture resistance R-curve and fatigue delamination propagation tests were carried out. It is found that the initiation value of the interface energy release rate is substantially lower for the wet-layup; whereas, their steady state values are quite similar. The fatigue delamination propagation tests were performed at various cyclic R-ratios. The delamination propagation rate da/dN was calculated from the experimental data and plotted using a modified Paris equation with different functions of the mode I energy release rate. As expected, the da/dN curves depend upon the R-ratio. By using another parameter based on the Hartman–Schijve equation for metals, it is possible to obtain a master-curve for all R-ratios. It is seen that the propagation rate for the prepreg is faster than that of the wet-layup.

Mixed mode interface fracture toughness of a multi-directional composite – UD/woven pair

Twenty-seven mixed mode Brazilian disk specimens were tested to obtain the fracture toughness of a delamination between two fiber reinforced composite plies in a multi-directional laminate, manufactured by means of a wet-layup. Using finite element analyses and conservative integrals, mechanical and residual curing stress intensity factors were found and used to calculate the interface energy release rate and phase angles. Based on these results, a three-dimensional failure criterion is proposed to obtain a failure surface. This criterion may be used to predict failure of a structure containing this material and interface.