Interfacial Fracture Resistance Research Articles

DCB Bonding Energy Measurement Using Confocal IR Microscopy

Direct bonding is a widely used technique in the semiconductor industry. Many materials can be assembled and stacked together with this technique, enabling the fabrication of many useful structures. The direct bonding technique is, for instance, a major step of the Smart Cut ™ process flow enabling the industrial-scale production of Silicon-On-Insulator (SOI) substrates [1][2]. Material diversification in the microelectronics industry (i.e. “More than Moore” approach) imposes new technological constraints. The substrate bonding process control has to be improved calling for more and more accurate bonding energy measurement protocols.In this work, a new technique is assessed in order to measure, at the wafer scale, direct bonding energies. It is derived from the standard Double Cantilever Beam (DCB) method [3] and uses interferometry in confocal IR laser source microscopy to measure crack openings (Fig. 1A) [4][5][6]. Such a bonding energy measurement protocol shows a better accuracy compared to other techniques (Fig. 1B & 1D). This is due to a better confocal microscopy resolution and the high intensity of the laser source. The elastic energy stored in bent wafers is obtained by measuring the beam curvature [7][8]. DCB deformation models are discussed from short-range crack opening to long distance beam-bending theories. Comparison is done between results from analytic models, Finite Element Model (FEM) and experiments (Fig. 1C).Near-bonding edge zone modeled with FEM simulation accurately matches experimental data. A new mechanical and universal bending model, valid at both small and large scales, is proposed. With this model, bonding energy extraction is then reduced to a simple scaling parameter extraction directly linked to the stored elastic strain energy (Fig 1C & 1D) [9]. This work opens prospects for deformation and bonding energy measurements in various configurations including bonded heterostructures, polymer, and metal bonding. [1] Bruel, Electron. Lett. 31, 1201 (1995).[2] K. Celler, A.-J. Auberton-Hervé, B. Aspar, C. Lagahe-Blanchard, and C. Maleville, in Wafer Bonding Applications and Technology, Springer Series in Materials Science, edited by M. Alexe and U. Gosele, Springer, Berlin (2004).[3] Maszara, G. Goetz, A. Caviglia, and J. B. Mckitterick, J. Appl. Phys. 64, 4943 (1988).[4] Wu, S. Gowrishankar, R. Huang et al., Int. J. Fract. 202, 1–19 (2016).[5] Gowrishankar, H. Mei, K. M. Liechti et al., Int. J. Fract. 177, 109–128 (2012).[6] Pallares, L. Ponson, A. Grimaldi, M. George, G. Prevot, and M. Ciccotti, Int. J. Fract. 156, 11–20 (2009).[7] Bertholet, “Measurement, optimization and multiscale modeling of silicon wafer bonding interface fracture resistance,” Ph.D. thesis (Catholique de Louvain, 2006).[8] Olbrechts, B. Lejeune, Y. Bertholet, T. Pardoen, and J.-P. Raskin, ECS Trans. 3(6), 279–289 (2006).[9] Colonel, A. Calvez, F. Fournel et al., J. Appl. Phys. 132, 215106 (2022). Fig. 1: A – (Top) Four pasted IR confocal microscope images acquired during the DCB testing (the vertical red dashed line shows the closing point’s fitted position). (Bottom) Air gap height measured as a function of pixel position.B – Simulated reflected intensity (left y-axis) and experimental reflected intensity (right y-axis), both as functions of the estimated distance from the closure point x. The vertical dashed grey line shows the real experimental closing point.C – Air gap height as a function of the position/thickness ratio (in log/log scales) for different analytical and numerical models and experimental data.D – Bonding energies including errors obtained with the standard length measurement method, the curvature interpolation method, the scaling method, or J-integral calculation from FEM as functions of the annealing temperature. Figure 1

Revealing the accelerated crack prolongation behavior under chemical ionomer degradation within the catalyst layer

As a critical electrochemical reaction region of the proton exchange membrane fuel cell (PEMFC), the cracking issue of the catalyst layer (CL) considerably affects the performance and durability of the PEMFC. However, the impact of chemical ionomer degradation on CL cracking has not been comprehensively revealed. This study investigates the effect of chemical ionomer degradation on CL cracking through accelerated stress tests, characterization, and theoretical analysis. The results indicate that the increasing chemical degradation degree facilitates CL cracking. The CL with the most severe chemical degradation has a single total crack length increment of 1.97 times for the novel CL under the same degree of mechanical degradation. CL fracture resistance analyses reveal that the decrease in interface fracture resistance is the predominant impulse in accelerating CL cracking. Furthermore, the cell voltage reduction of the CL with the most severe chemical degradation during mechanical degradation is 34.22 mV at the current density of 1800 mA cm−2, which is 1.82 times for the fresh CL. The increment of activation resistance and mass transfer resistance are the main causes of the larger cell performance loss. The above findings emphasize the significance of high interface fracture resistance in inhibiting CL cracking and offer theoretical support for analyzing post-operational CL cracking.

Mode I and Mode II interfacial fracture energy of SiC/BN/SiC CMCs

Quantifying the mixed mode fracture toughness of interfaces in ceramic matrix composites (CMCs) is crucial for understanding their failure. In this work we use in situ micromechanical testing in the scanning electron microscope to achieve stable interfacial crack propagation in Mode I (Double Cantilever Beam) and Mode II (Push out) and measure the corresponding fracture resistances. We use this approach to measure the interfacial fracture resistance in SiC/BN/SiC CMCs and compare it to the fracture energy of the fibres. During in-situ testing, fracture paths can be observed while data is acquired simultaneously. We clearly observe debonding at the BN-fibre interface (i.e. inside adhesive debonding). The critical energy release rate of the BN-fibre interface for Mode I and II (GIc ≈ 2.1 ± 1.0 J/m2 and GIIc ≈ 1.2 ± 0.5 J/m2) are equivalent and is lower than that measured for the fibre using microscopic DCB tests (GIc ≈ 6.0 ± 2.0 J/m2). These results explain the generalized fibre debonding and pull out observed in the fracture of these CMCs. By enabling direct observation of crack paths and quantifying the corresponding fracture energies, we highlight possible routes for the optimisation and modelling of the new generation of CMC interphases.

Could different direct restoration techniques affect interfacial gap and fracture resistance of endodontically treated anterior teeth?

ObjectivesTo evaluate different direct restoration techniques on various cavity designs in anterior endodontically treated teeth (ETT).Materials and methodsNinety upper central incisors (n = 90) were selected, endodontically treated, and divided into three groups (n = 30) accordingly to the cavity design: minimal endodontic cavity access (group A), endodontic access + mesial class III cavity (group B), and endodontic access + two class III cavities (group C). Three subgroups (n = 10) were then created accordingly to the restoration technique: nano hybrid composite restoration (subgroup a), glass fiber post + dual-cure luting cement (subgroup b), and bundled glass fiber + dual-cure luting cement (subgroup c). Samples underwent micro-CT scan, chewing simulation, and a second micro-CT scan. 3D quantification (mm3) of interfacial gap progression was performed; then, samples underwent fracture resistance test. Data were statistically analyzed setting significance at p < 0.05.ResultsGroups A and B showed significantly lower interfacial gap progression compared with group C. Subgroup b performed significantly better compared with subgroups a and c. Improved fracture strength was reported for group C compared with group A, while both subgroups b and c performed better than subgroup a.ConclusionsCavity design significantly influenced interfacial gap progression and fracture resistance. Fiber posts significantly lowered gap progression and improved fracture resistance while bundled fibers only increased fracture resistance. A significant reduction of non-repairable fractures was recorded when fibers were applied.Clinical relevanceA minimally invasive approach, conserving marginal crests, should be applied whenever possible. Inserting a fiber post is indicated when restoring anterior ETT, in order to reduce gap progression, improve fracture resistance, and avoid catastrophic failures.

An experimental study of the interfacial fracture behavior of Titanium/CFRP adhesive joints under mode I and mode II fatigue

In the present paper, the mode I and II fatigue fracture performance of a novel Titanium/CFRP adhesive joint is investigated. The adhesive joint under study is composed of two thin adherents, one Titanium sheet and one CFRP laminate, and is reinforced from both sides with two thick aluminum beams to increase its flexural stiffness and ensure the non-yielding of the Titanium. The interfacial fracture resistance is in the focus and aspects such as the loading that defines the crack propagation threshold as well as the utilization of an appropriate Paris-like law to optimally describe the experimental data are under investigation.

3D Interfacial Gap and Fracture Resistance of Endodontically Treated Premolars Restored with Fiber-reinforced Composites.

To evaluate interfacial gap and fracture resistance of endodontically treated maxillary premolars, restored with different glass-fiber reinforced materials. Eighty-four extracted intact premolars were endodontically treated and MOD cavities prepared. Specimens were divided into 7 groups (n = 12 for each) as follows: sound teeth (G1); no restoration (G2); direct composite restoration with fiber-reinforced composite (everX Posterior GC) (G3); direct composite restoration (Filtek Supreme XTE, 3M Oral Care; "FSXTE") (G4); a horizontal layer of high-viscosity flowable composite (G-ænial Flow, GC) was placed on the pulp chamber floor, 10 mm x 3 mm glass fibers (everStick NET, GC) were inserted into the cavity (G5); same procedure as in group 5 except the direct restoration was made incrementally with FSXTE (3M Oral Care) (G6); composite overlays were placed (G7). Specimens were scanned with micro-CT to evaluate 3D interfacial gaps before and after chewing simulation using Mimics software to calculate voids between restoration and tooth (dentin and enamel). These data (in mm3) were collected for statistical analysis. Thereafter, specimens were loaded to fracture using a universal testing machine. Maximum breaking loads were recorded in Newton (N). The data obtained were analyzed using two-way ANOVA and post-hoc Tukey's test (p < 0.05). ANOVA showed that horizontal glass-fiber insertions statistically significantly reduced interfacial gaps after chewing simulation. No differences in fracture resistance were found between Filtek Supreme XTE and everX Posterior; moreover, glass-fiber insertion did not significantly improve fracture resistance in either case. Composite overlays achieved significantly better fracture toughness than did direct restorations. For the direct restoration of endodontically treated premolars, the insertion of glass fibers into direct composite restorations was unable to guarantee a significant increase in the fracture resistance or a significant change in the fracture pattern. However, it significantly reduced interfacial gap volume after cycling fatigue.

Interfacial Gap and Fracture Resistance of Indirect CAD-CAM Restorations

Interfacial Gap and Fracture Resistance of Indirect CAD-CAM Restorations

Combining interface damage and friction in cohesive interface models using an energy based approach

Cohesive zone models coupling interface damage and friction have been developed in the literature and are available in the commercial finite element package ABAQUS to consider the enhancing effect of through-thickness compression on interfacial fracture resistance. It is revealed in this paper that these models are extremely dependent on interface stiffness, because interface stiffness reduction factor is used to combine damage and friction in these models. The interfacial constitutive law converges but only when the interface is extremely stiff and an unrealistic evolution of the interface damage is produced. A new approach is then developed which uses a cohesive energy related parameter to combine interface damage and friction. The behaviour of the new coupled model is independent of the interface stiffness once the interface is moderately stiff. The new and existing damage/friction coupled models have been employed to simulate the shear failure of a composite specimen and the predictions are compared against the experimental data in the literature. The new model produces converged results over a wide range of interface stiffness and the predictions match the experiments quite well, better than the existing models.

Bioactive glass–chitosan composite coatings on PEEK: Effects of surface wettability and roughness on the interfacial fracture resistance and in vitro cell response

To improve the osteointegration of polyetheretherketone (PEEK) spinal fusions, the 45S5 bioactive glass® (BG)-chitosan (CH) composite was used to coat the PEEK by a dip-coating method at room temperature. A robust bonding between the BG-CH composite coating and the PEEK was achieved by a combined surface treatment of sand blasting and acid etching. The effects of surface wettability and surface roughness on the adhesion of the BG-CH composite coating were characterized by fracture resistance (Gc), respectively, measured by four-point bending tests. Compared with the surface polar energy (wettability), the surface roughness (>3 μm) played a more important role for the increase in Gc values by means of crack shielding effect under the mixed mode stress. The maximum adhesion strength (σ) of the coatings on the modified PEEK measured by the tensile pull-off test was about 5.73 MPa. The in vitro biocompatibilities of PEEK, including cell adhesion, cell proliferation, differentiation, and bioactivity in the stimulated body fluid (SBF), were enhanced by the presence of BG-CH composite coatings, which also suggested that this composite coating method could provide an effective solution for the weak PEEK-bone integration.

Mechanisms governing the failure modes of dense vertically cracked thermal barrier coatings

The introduction of dense vertical cracks in ceramic top coat has been recognized as an efficient way to improve the strain tolerance and service durability of thermal barrier coatings (TBCs). However, further growth of these pre-existing cracks may cause the delamination of the coatings to form various failure modes. The motivation of this work is to numerically study the mechanisms that govern the formation of failure modes in dense vertically cracked TBCs. The effects of vertical crack density and material properties on the fracture behaviors are discussed. An energy-based criterion is employed to deal with the surface crack deflection/penetration behavior at a bimaterial interface, and an interaction integral method for discontinuous materials is utilized to evaluate the fracture parameters. The failure maps of TBCs are constructed by examining the continuous variations of crack tip driving forces over the whole fracture process. It is verified that the interfacial fracture resistance could be enhanced by introducing high-density vertical cracks. At the same time, these cracks tend to penetrate into the bond coat that results in debonding at bond coat/substrate interface or at both interfaces. In addition to benefit in alleviating the interfacial mismatch stress, it is found that the high-density vertical cracks give toughening increases to the coating system by releasing more energy from multiple paths. Moreover, the effects of mixed-mode interface toughness and initially residual stress on the formations of failure mode are discussed.

Using glass-graded zirconia to increase delamination growth resistance in porcelain/zirconia dental structures

ObjectivePorcelain fused to zirconia (PFZ) restorations are widely used in prosthetic dentistry. However, their tendency to delaminate along the P/Z interface remains a practical problem so that assessing and improving the interfacial strength are important design aspects. This work examines the effect of modifying the zirconia veneering surface with an in-house felspathic glass on the interfacial fracture resistance of fused P/Z. MethodsThree material systems are studied: porcelain fused to zirconia (control) and porcelain fused to glass-graded zirconia with and without the presence of a glass interlayer. The specimens were loaded in a four-point-bend fixture with the porcelain veneer in tension. The evolution of damage is followed with the aid of a video camera. The interfacial fracture energy GC was determined with the aid of a FEA, taking into account the stress shielding effects due to the presence of adjacent channel cracks. ResultsSimilarly to a previous study on PFZ specimens, the fracture sequence consisted of unstable growth of channel cracks in the veneer followed by stable cracking along the P/Z interface. However, the value of GC for the graded zirconia was approximately 3 times that of the control zirconia, which is due to the good adhesion between porcelain and the glass network structure on the zirconia surface. SignificanceCombined with its improved bonding to resin-based cements, increased resistance to surface damage and good esthetic quality, graded zirconia emerges as a viable material concept for dental restorations.

A cohesive zone model taking account of the effect of through-thickness compression

Experiments in the literature show that through-thickness compressive stress significantly enhances interfacial fracture resistance. Most existing cohesive zone and interface element models which consider the enhancement only introduce friction in the model. In this paper, a new method is proposed to include both friction and enhanced interfacial shear strength in a cohesive zone model. Contact and friction at micro/macro crack closure is added to the cohesive constitutive law. A traction-based failure function and an energy-based failure function are employed and combined to construct a damage surface. An enhancement of interfacial shear strength due to through-thickness compressive stress is introduced into the traction-based function which governs the damage initiation, while the energy-based function controls the damage growth. The damage surface shrinks in the traction space as damage develops and leads to a softening cohesive constitutive law. The model is employed to simulate shear failure of symmetric double notch specimens and delamination failure in specimens with cut- and dropped-plies. Numerical predictions are in good agreement with available experimental data in the literature. Parametric studies show that both the friction at crack closure and enhancement of the interfacial shear strength play an important role in enhancing fracture resistance.

Determination of mode I &amp; II strain energy release rates in composite foam core sandwiches. An experimental study of the composite foam core interfacial fracture resistance

Abstract The use of composite materials is on the rise in different engineering fields. Following this trend the wind turbine industry has adopted composites as their primary material of choice. For wind turbine blades having large unsupported functional aerodynamic surfaces; the structural stiffness is very important. Stiffness is required to keep the deformations to a minimum under aerodynamic forces. The blade is thus stiffened using sandwich structures at high strain locations within the structure. The lightweight foam cored sandwiches though add stiffness, at the same time pose a challenge for design as the difference in stiffness of both the face-plate and the foam core is very high. The resistance to fracture in any part of the structure is an important design parameter to be determined. The determination of fracture resistance quantified here as the Strain Energy Release Rate (SERR) poses some unique challenges when dealing with highly heterogeneous materials in terms of stiffness. In this study some approaches have been analyzed while others are developed to tackle this problem and to measure the Mode I & II SERR of the face-plate foam-core interface. The sandwich core varies in both thickness and density depending on the loading and thus the location along the blade length. However for this study we have used a single density of foam core for the most part of the turbine blade. Different thicknesses of the foam cores are used to determine the effect of scale on the calculated SERR.

Enhancing the fracture resistance of carbon fiber reinforced SiC matrix composites by interface modification through a simple fiber heat-treatment process

A simple method to significantly increase the toughness of carbon fiber reinforced SiC matrix composites is presented. The method is based on the heat treatment of Toray T300 carbon fibers in vacuum, leading to the in-situ formation of carbon coatings on the fiber surface that optimizes the interfacial strength in carbon fiber reinforced SiC matrix composite. The formation mechanism of the in-situ coatings was studied by transmission electron microscopy, and the effects of the in-situ carbon interphase on the interfacial property and fracture resistance of the composites were comprehensively assessed by combining transmission electron microscopy, fiber push-in and macro mechanical testing. The results reveal that the in-situ coating was originated from the pyrolysis of the proprietary sizing of the T300 fibers, that was crystallized during thermal treatment, maintaining a low oxygen content. For this reason, the resulting coating can effectively hinder the interfacial reactions in carbon fiber reinforced SiC composites, and remarkably weaken the composite interfacial shear strength from 105 ± 10 MPa to 30 ± 5 MPa. Due to the introduction of in-situ carbon interphase, the toughness of the carbon fiber reinforced SiC composite increased significantly from 1.7 ± 0.3 MPa m1/2 to 21.3 ± 0.7 MPa m1/2, triggered by toughening mechanisms such as crack deflection and fiber pullout.

On the interfacial fracture resistance of resin-bonded zirconia and glass-infiltrated graded zirconia

ObjectiveA major limiting factor for the widespread use of zirconia in prosthetic dentistry is its poor resin-cement bonding capabilities. We show that this deficiency can be overcome by infiltrating the zirconia cementation surface with glass. Current methods for assessing the fracture resistance of resin-ceramic bonds are marred by uneven stress distribution at the interface, which may result in erroneous interfacial fracture resistance values. We have applied a wedge-loaded double-cantilever-beam testing approach to accurately measure the interfacial fracture resistance of adhesively bonded zirconia-based restorative materials. MethodsThe interfacial fracture energy GC was determined for adhesively bonded zirconia, graded zirconia and feldspathic ceramic bars. The bonding surfaces were subjected to sandblasting or acid etching treatments. Baseline GC was measured for bonded specimens subjected to 7 days hydration at 37°C. Long-term GC was determined for specimens exposed to 20,000 thermal cycles between 5 and 55°C followed by 2-month aging at 37°C in water. The test data were interpreted with the aid of a 2D finite element fracture analysis. ResultsThe baseline and long-term GC for graded zirconia was 2–3 and 8 times greater than that for zirconia, respectively. More significantly, both the baseline and long-term GC of graded zirconia were similar to those for feldspathic ceramic. SignificanceThe interfacial fracture energy of feldspathic ceramic and graded zirconia was controlled by the fracture energy of the resin cement while that of zirconia by the interface. GC for the graded zirconia was as large as for feldspathic ceramic, making it an attractive material for use in dentistry.

Comparison of coupon and full-scale determination of energy release rate for bonded composite repairs of pressure equipment

Bonded composite repairs of pressure equipment intended to rehabilitate a through-wall defect are governed by the fracture resistance of interface between the composite and the substrate. This fracture-dominated failure mode requires a detailed understanding of the fracture energy of the composite–substrate interface. Current approaches for measuring this interfacial fracture energy use simulated repairs on small-scale pressure vessels. In this paper we describe a simple coupon-based test using a width-tapered-double-cantilevered beam specimen. Fracture energies determined using the coupon-based approach were in close agreement with values back calculated from full-scale testing performed on simulated through-wall defects.

Interfacial Creep Fracture Behavior of Foam Core Sandwich Composites with Different Resin

Interfacial creep fracture behavior of sandwich composites consisting of E-glass/ unsaturated polyester (UPE) resin and E-glass/vinyl ester (VE) resin facings over PMI foam core has been experimentally investigated. Digital image correlation (DIC) method was employed in the double cantilever beam (DCB) test to measure the creep displacement field surrounding the crack tip. Crack opening displacements (COD) at various creep time were extracted from the creep displacement field and mode I stress intensity factors were determined using the small region COD-based linear extrapolation method. Significant increments of COD and nominal stress intensity factor are found in specimen with UPE resin and specimen with VE resin after 24 hours creep test. It is also found that specimen with UPE resin has a better interfacial creep fracture resistance than that of specimen with VE resin.

Toughness enhancement in architecturally modified Al6061-5 vol.% SiCp laminated composites

Damage tolerance improvement in discontinuously reinforced aluminum matrix composites has been examined through both extrinsic and intrinsic approaches by researchers. In this study, extrinsic mechanism was considered in the form of architectural modification in laminates comprising two exterior layers of Al6061-5 vol.% SiCp and an interlayer of Al1050. Hot roll bonding was utilized to fabricate laminates since interfacial adhesion of layers was controlled by means of rolling strain. The interfacial strength and fracture resistance of specimens were examined by shear and three-point bending test, respectively. Achievements demonstrated that the quasi-static toughness of laminates tested in crack divider orientation was greater than that of monolithic samples. Also, it was revealed that the initiation, propagation, and total toughness were influenced by interfacial adhesion. In the other words, interfacial bonding played a major role in energy absorption during fracture. Enhancement of the interfacial adhesion by an increment in rolling strain elevated the energy consumed for emergence and growth of debonded area.

Interfacial fracture resistance of the joint of a solid oxide fuel cell glass–ceramic sealant with metallic interconnect

Interfacial cracking resistance of a joint between a glass–ceramic sealant (GC-9) and interconnect stainless steel (Crofer 22 H) for planar solid oxide fuel cells is investigated. Interfacial fracture energy is measured at room temperature to 800 °C using a four-point bending test technique. A heat treatment of 100 h or 1000 h at 800 °C is applied for studying the thermal aging effect. Results show the variation trend of interfacial fracture energy with temperature is similar for all given material conditions. Interfacial fracture energy increases with temperature to reach a peak value at 700 °C and then drops at temperature above 700 °C. A 100-h aging treatment does not change the interfacial fracture energy significantly, compared to the non-aged condition. The 1000 h-aged joint, however, has greater interfacial fracture energy than the non-aged and 100 h-aged joints at 700 °C–800 °C. Two types of cracking path in the interior of fracture surface are identified. Firstly, delamination takes place at the interface between the glass–ceramic substrate and chromate layer. Secondly, cracking occurs within the chromate layer. However, for the 1000 h-aged joints tested at 700 °C–800 °C, fracture at the highly oxidized, peripheral regions takes place within the glass–ceramic layer.

Adhesion Improvement of Glass-Fibre-Reinforced Polyester Composites by Gliding Arc Discharge Treatment

A gliding arc is a plasma that can be operated at atmospheric pressure and applied for plasma surface treatment for adhesion improvement. In the present work, glass-fibre-reinforced polyester plates were treated using an atmospheric pressure gliding arc discharge with an air flow to improve adhesion with a vinylester adhesive. The treatment improved wettability and increased the polar component of the surface energy and the density of oxygen-containing polar functional groups at the surfaces. Double cantilever beam specimens were prepared for fracture mechanics characterisation (fracture resistance as a function of nominal mode mixity) of the laminate adhesive interface. It was found that gliding arc treatment significantly increases the interfacial fracture energy and fracture resistance in comparison with a standard peel ply treatment, although the mixed mode fracture energy of the gliding arc treated specimen was not as high as that of the laminate itself.