Critical Fracture Load Research Articles

The internal modified layer structure of silicon carbide induced by ultrafast laser and its application in stealth dicing

Silicon carbide (SiC) is widely applied in high-power electronic devices due to its excellent properties. Stealth dicing (SD) as one of the dicing methods, exhibits the advantages of few thermal surface damage and low edge-chipping. In this study, we use an ultrafast laser to induce the modified layer structure inside the SiC wafers. The effects of laser processing parameters on the modified layers are studied. The formation mechanism of the modified layer and its influence on SD are analyzed. The result shows that the number of modified layer structures is mainly determined by the moving velocity. The different modified layer structures will affect the surface roughness of the SD cross-section and critical fracture load of the 4H–SiC wafers. Finally, we achieved the high-quality SD of SiC wafers, and a cross-section with the minimum surface roughness is approximately 381 nm.

Fracture toughness and slow crack growth behaviour of metal-proton conducting ceramic composites

The fracture toughness and slow crack growth behaviour of two load-bearing metal ceramic components adopted in negatrode-supported electrochemical devices, namely Ni-BCZY27 and Ni-BCZY442, are investigated via double torsion technique.The investigation showed that the two metal-ceramic composites are considerably less sensitive to slow crack growth when compared to oxide ceramics such as stabilized zirconia and alumina, with KI0/KIC equal to approximately 0.8. On the other hand, they also showed lower fracture toughness than Ni-3YSZ, with Ni-BCZY442 and Ni-BCZY27 having a fracture toughness of respectively 1.74 and 3.04 MPa*m1/2 for porosities equal to 25.8% and 19.1% respectively, compared to Ni-3YSZ reported in previous work with similar Ni content and porosity of approximately 30% having a fracture toughness equal to 3.4 MPa*m1/2. Furthermore, the analysis of samples presenting extensive barium depletion indicated fast fracture propagation upon application of loads significantly lower than the critical fracture load.

The effect of loading rate on mixed mode I/II fracture behavior of adhesively bonded joints: Experimental and numerical approach

In this study, the use of a modified Arcan fixture to investigate the fracture behavior of adhesively bonded Al/Al joints has been discussed under rate-dependent loading in various loading conditions (mode I, mode II, and mixed mode (I/II)). It was observed that the testing speed has a significant effect on the fracture properties of the joints, especially in pure mode, II. The results indicated that failure load was increased for all three loading modes and an increase was also observed for strain energy release rate at all loading conditions. The critical fracture loads obtained from the experimental tests were used to calculate the values of the critical stress intensity factors and strain energy release rates for loading modes I, II, and mixed mode I/II at different loading rates by using the finite element method. It was shown that the values of strain energy release rate for loading mode II were higher than mode I and mixed mode at all loading speeds. Finally, scanning electron microscope analyses (SEM) were used to investigate the effects of loading speed on the failure surfaces of the adhesive in microstructural scales and it was shown that at low loading rates, the number of crazes that cause failure in the adhesive layer increases.

Study on crack propagation behavior of bridge deck asphalt pavement

Crack is a typical distress on bridge deck asphalt pavement (BDAP), which destroys the integrity and continuity of the pavement structure. However, the research on the crack propagation mechanism of BDAP is still limited. In this study, the three-point bending test was performed to investigate the propagation process of cracks in BDAP. Pre-cracks were set in the specimens with different depths (8 mm, 12 mm, 15 mm) and 4 mm widths, and two asphalt rubber hot-mix (ARHM) mixtures (ARHM-13 and ARHM-20) were selected. The critical fracture load, fracture energy, and fracture toughness were compared to investigate the crack resistance of ARHM-13 and ARHM-20 mixtures. In addition, the upper and lower layers of double-layer composite pavement specimens were fabricated with ARHM-13 and ARHM-20 mixture, respectively. The propagation process of the top-down crack (TDC) and reflection crack (RC) were investigated at different locations on the specimens. The test results show that the crack resistance of ARHM-20 mixtures is greater than that of ARHM-13 mixtures, and ARHM-20 mixtures should be used in the lower layer of BDAP to limit the propagation process of the reflection crack to the upper layer. The cracks propagated firstly from the RC and formed a through crack at the TDC in the specimens under the three-point bending loading action. The presence of TDC was found to accelerate the crack propagation of RC and exacerbate the failure of the BDAP. The crack length and deflection angle were determined by the pre-crack location. Furthermore, the decrease in temperature led to an increase in crack propagation velocity. The average propagation velocity increased from 0.03 mm/s to 0.55 mm/s as the temperature decreased from 20 ℃ to −20 ℃.

Fracture load in double keyhole notch PLA-Cu2O nanocomposites manufactured via compression molding and 3D printing: An experimental and numerical study

Polylactic acid (PLA) polymer has garnered significant attention due to its biocompatibility. The incorporation of copper oxide (Cu2O) nanoparticles into this polymer is expected to enhance its antibacterial, electrical, and thermal properties. This modification can potentially improve the performance of PLA in the fields of prosthetics manufacturing or printed circuit fabrication. However, the current research is rather focused on the mechanical properties of the PLA-Cu2O nanocomposites. This research is thus aimed to analyze PLA-Cu2O (97-3 wt%) nanocomposites with a double keyhole notch configuration both experimentally and numerically. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray mapping of elemental distribution(X-map), and thermogravimetric analysis (TGA) were employed to explore the morphology, crystallinity, homogeneity, purity, and thermal stability of the nanocomposite. The specimens were fabricated through two different processes: the classical method of compression molding and the innovative method of 3D printing. The results revealed the superior mechanical performance of the 3D-printed nanocomposite at a 0° raster angle, while the mechanical properties gradually decreased for raster angles of 45° and 90°. The experimental test also indicated a decline in the maximum fracture load of specimens with a double keyhole notch and constant notch inclination angle by raising the notch radius. This behavior was also observed by increasing the notch inclination angle at constant notch radius. The numerical results were similar to the experimental findings. Moreover, the nanocomposite manufactured through the classical method exhibited higher critical fracture load compared to their 3D-printed counterparts with the same geometry.

Моделирование упругопластического разрушения компактного образца

The strength of a compact specimen under normal fracture (fracture mode I) is studied within the framework of the Neuber-Novozhilov approach. A model of an ideal elasto-plastic material with limiting relative elongation is chosen as the model of the deformable solid. This class of materials includes low-alloy steels that are used in structures operating at temperatures below the cold brittleness threshold. The crack propagation criterion is formulated using the modified Leonov-Panasyuk-Dugdale model, which uses an additional parameter, i.e., the diameter of the plasticity zone (the width of the prefracture zone). In the case of stress field singularity occurring in the vicinity of the crack tip, a two-parameter (coupled) criterion for quasi-brittle fracture is developed for type I cracks in an elastoplastic material. The coupled fracture criterion includes the deformation criterion attributed to the crack tip and the force criterion attributed to the model crack tip. The lengths of the original and model cracks differ by the length of the prefracture zone. Diagrams of the quasi-brittle fracture of the specimen under plane strain and plane stress conditions are constructed. The constitutive equations of the analytical model are analyzed in terms of the characteristic linear dimension of the material structure. Simple formulas applicable to verification calculations of the critical fracture load and pre-fracture zone length for quasi-brittle and quasi-ductile fractures are obtained. The parameters in the presented model of quasi-brittle fracture are analyzed. It is proposed to select the parameters of the model according to the approximation of the uniaxial tension diagram and the critical stress intensity factor.

INCREASING THE WEAR RESISTANCE OF TITANIUM ALLOYS BY DEPOSITION OF A MODIFYING COATING (Zr,Nb)N

The possibility of increasing the wear resistance of titanium alloy parts by depositing a zirconium-niobium-nitrogen [(Zr,Nb)N] coating with an adhesive Zr,Nb sublayer on their surfaces was investigated. Given that the Vickers hardness of this coating is HV = 2336 ± 115, and the value of the critical fracture load during the scratch test is L<sub>C2</sub> = 14 N, which is noticeably lower compared to nitride coatings deposited on a carbide or ceramic substrate, the (Zr,Nb)N coating provides a noticeable increase in wear resistance. The wear rate of the uncoated sample was 2.5 times higher compared to the (Zr,Nb) N-coated sample. Coating deposition allows simultaneously reducing the friction coefficient (from 0.45 for an uncoated sample to 0.33 for a coated sample) and increasing the wear resistance.

Brewing sustainability and strength: Biocomposite development through tea waste incorporation in polylactic acid

This study aims to enhance the mechanical properties of polylactic acid by incorporating black tea waste as an economical and sustainable additive capable of being recycled. The black tea waste, after the hot water color removal process, is milled to a fine and uniform powder size. The combination of these particles with polylactic acid is carried out using a twin-screw extruder. Specimens of pure polylactic acid and biocomposites containing 3 and 5 wt% black tea waste are manufactured using a hot press machine at a temperature of 200 °C. The filaments are also successfully extruded for three-dimensional printing purposes. Scanning electron microscopy images reveal that in the polylactic acid–3% tea biocomposite, the tea particles are appropriately dispersed within the polylactic acid matrix. The tensile test results indicate that biocomposite polylactic acid-3% tea has the highest mechanical properties, with a tensile strength of 67 MPa, demonstrating a 34% increase compared to polylactic acid. Furthermore, the biocomposite of polylactic acid–3% tea waste exhibits the best performance with a fracture energy of 2.5 kJ/m2 in the impact test. Hence, polylactic acid–3% tea biocomposite can be recommended as a suitable sustainable substitute. Finally, numerical simulations are performed on biocomposites containing double keyhole notches. This analysis is conducted to observe the behavior of biocomposite models with double keyhole notch under mixed-mode loading. The critical fracture load of the models is calculated using the strain energy density criterion. It is observed that an increase in the notch inclination angle and notch radius leads to a decrease in the fracture load in the models.

How mangabey molar form differs under routine vs. fallback hard-object feeding regimes

Background Components of diet known as fallback foods are argued to be critical in shaping primate dental anatomy. Such foods of low(er) nutritional quality are often non-preferred, mechanically challenging resources that species resort to during ecological crunch periods. An oft-cited example of the importance of dietary fallbacks in shaping primate anatomy is the grey-cheeked mangabey Lophocebus albigena. This species relies upon hard seeds only when softer, preferred resources are not available, a fact which has been linked to its thick dental enamel. Another mangabey species with thick enamel, the sooty mangabey Cercocebus atys, processes a mechanically challenging food year-round. That the two mangabey species are both thickly-enameled suggests that both fallback and routine consumption of hard foods are associated with the same anatomical feature, complicating interpretations of thick enamel in the fossil record. We anticipated that aspects of enamel other than its thickness might differ between Cercocebus atys and Lophocebus albigena. We hypothesized that to function adequately under a dietary regime of routine hard-object feeding, the molars of Cercocebus atys would be more fracture and wear resistant than those of Lophocebus albigena. Methods Here we investigated critical fracture loads, nanomechanical properties of enamel, and enamel decussation in Cercocebus atys and Lophocebus albigena. Molars of Cercopithecus, a genus not associated with hard-object feeding, were included for comparison. Critical loads were estimated using measurements from 2D µCT slices of upper and lower molars. Nanomechanical properties (by nanoindentation) and decussation of enamel prisms (by SEM-imaging) in trigon basins of one upper second molar per taxon were compared. Results Protocone and protoconid critical fracture loads were significantly greater in Cercocebus atys than Lophocebus albigena and greater in both than in Cercopithecus. Elastic modulus, hardness, and elasticity index in most regions of the crown were greater in Cercocebus atys than in the other two taxa, with the greatest difference in the outer enamel. All taxa had decussated enamel, but that of Cercocebus atys uniquely exhibited a bundle of transversely oriented prisms cervical to the radial enamel. Quantitative comparison of in-plane and out-of-plane prism angles suggests that decussation in trigon basin enamel is more complex in Cercocebus atys than it is in either Lophocebus albigena or Cercopithecus cephus. These findings suggest that Cercocebus atys molars are more fracture and wear resistant than those of Lophocebus albigena and Cercopithecus. Recognition of these differences between Cercocebus atys and Lophocebus albigena molars sharpens our understanding of associations between hard-object feeding and dental anatomy under conditions of routine vs. fallback hard-object feeding and provides a basis for dietary inference in fossil primates, including hominins.

Predicting Critical Loads in Fused Deposition Modeling Graphene-Reinforced PLA Plates Containing Notches Using the Point Method.

The use of 3D-printed composites in structural applications beyond current prototyping applications requires the definition of safe and robust methodologies for the determination of critical loads. Taking into account that notches (corners, holes, grooves, etc.) are unavoidable in structural components, the presence of these types of stress risers affects the corresponding load-carrying capacity. This work applies the point method (PM) to the estimation of the critical (fracture) loads of graphene-reinforced polylactic acid (PLA-Gr) plates obtained via fused deposition modeling (FDM) with a fixed raster orientation at 45/-45. Additionally, the plates contain three different notch types (U-notches, V-notches, and circular holes) and comprise various thicknesses (from 5 mm up to 20 mm) and ratios of notch length to plate width (a/W= 0.25 and a/W = 0.50). The comparison between the obtained experimental critical loads and the corresponding estimations derived from the application of the PM reveals that this approach generates reasonable accuracy in this particular material that is comparable to the accuracy obtained in other structural materials obtained via traditional manufacturing processes.

Experimental and numerical studies on the mechanical properties and behaviors of a novel wood dowel reinforced dovetail joint

To improve the mechanical strength of dovetail joints, resisting and postponing the crack propagation, a novel method of enhancing the mechanical strength of the dovetail joint using a dowel-reinforced method was proposed. The connection technical parameters of the dowel-reinforced dovetail joint (DRDJ) were investigated and optimized based on experimental and numerical methods. The results showed that there were three typical mechanical behaviors of the DRDJ characterized, and each of them can be separated into three regions, i.e., elastic region, crack propagation region, and failure region, by the defined crack initiation point and critical fracture point. The effects of dowel inserting distance and depth on mechanical properties of the DRDJ was significant. The proposed method was validated experimentally to be an efficient approach to improving the crack initiation load, critical fracture load, and elastic stiffness, and delay crack propagation. The connection technical parameters of the DRDJ were analyzed based on response surface method and experimentally validated to be the distance of 18.56 mm and depth of 32.19 mm. Tensile strength of the DRDJ was seriously influenced by wood dowel species and dowel fit, and increased with the increase of dowel fit and mechanical strength of wood dowel based on numerical analysis. In conclusion, the dowel-reinforced method is capable of improving the mechanical strength of dovetail joints, resisting and postponing the crack propagation, and has an advantage on the risk of pre-warning of wood structure failure.

Study on picosecond laser stealth dicing of 4H-SiC along [[formula omitted]] and [[formula omitted]] crystal orientations on Si-face and C-face

Stealth dicing of semi-insulating 4H-SiC along [112¯0] and [11¯00] crystal orientations on Si-face and C-face was conducted by using infrared picosecond laser in combination with three-point bending split. It was demonstrated that the laser ablation points inside 4H-SiC samples, the critical fracture load, and the dicing quality of 4H-SiC samples were closely related to the crystal orientation. The critical fracture load of 4H-SiC along [112¯0] orientation is smaller than that along [11¯00] orientation. The longitudinal lengths of the laser ablation points increase with the increase of laser incident distance. For the same laser-modified layer, as laser was incident from C-face and processed along [112¯0] orientation, the laser ablation points have larger longitudinal length. The reasons for the impact of crystal orientation on laser-modified points were analyzed. The fractured 4H-SiC samples have chipping width less than 3 μm and section roughness less than 500 nm. Moreover, the dicing quality along [112¯0] orientation is better than that along [11¯00] orientation. This research can provide technical support for precision dicing of SiC wafers in semiconductor industry.

Influence of Cutting Speed during the Turning of Inconel 718 on Oxidation Wear Pattern on the Zr-ZrN-(Zr,Mo,Al)N Composite Nanostructured Coating

The properties and oxidation wear patterns in the composite nanostructured coating of Zr-ZrN-(Zr,Mo,Al)N were studied during the turning of Inconel 718 alloy at the cutting speeds of vc = 125 and 200 m/min. The hardness of the coating, its elastic modulus, and critical fracture load during the scratch testing were determined. The study focused on the tribological properties of the Zr-ZrN-(Zr,Mo,Al)N coating at temperatures of 400–900 °C paired with an insert made of Inconel 718, which exhibited a certain advantage over the reference coatings of Zr-ZrN and Ti-TiN-(Ti,Cr,Al)N of similar thickness. The coating of Zr-ZrN-(Zr,Mo,Al)N provided for the longest tool life at the cutting speed of vc = 125 m/min (the tool life was four times longer in comparison with that of the uncoated tool and 15% longer in comparison with that of the Ti-TiN-(Ti,Cr,Al)N-coated tool) and at the cutting speed of vc = 200 m/min (the tool life was 2.5 times longer in comparison with that of the uncoated tool and 75% longer in comparison with that of the Ti-TiN-(Ti,Cr,Al)N-coated tool). While at the cutting speed of vc = 125 m/min, the surface coating layers exhibit only partial oxidation of the external layers (to a depth not exceeding 250 nm), with mostly preserved cubic nitride phases, and then the cutting speed of vc = 200 m/min leads to almost complete oxidation (to the depth of at least 500 nm), however, with a partially preserved nanolayered structure of the coating.

Mechanical Properties of New Generations of Monolithic, Multi-Layered Zirconia.

New monolithic multi-layered zirconia restorations are gaining popularity due to their excellent aesthetic properties. However, current knowledge of these newest multi-layer ceramics in terms of mechanical properties is scarce. Three monolithic, multi-layered zirconia materials (Katana, Kuraray Noritake, Japan) were selected for comparison: High Translucent Multi-layered zirconia (HTML), Super Translucent Multi-layered zirconia (STML) and Ultra Translucent Multi-layered zirconia (UTML). Fifteen specimens per group were cut from pre-sintered blocs in each of the four layers (L1, L2, L3, L4) and in different thicknesses (0.4 mm, 0.8 mm and 1.2 mm). Critical fracture load (Fcf) was recorded in 3-point-bending. Flexural strength (σ) in MPa, Vickers hardness (HV) in N/mm2, fracture toughness (KIc) in MPa*m1/2, Weibull Modulus (m) and characteristic Weibull strength (σw) in MPa were assessed. Statistical analysis was performed using ANOVA analysis. FS and KIc were significantly higher (p < 0.05) for Katana™ HTML (652.85 ± 143.76-887.64 ± 118.95/4.25 ± 0.43-5.01 ± 0.81) in comparison to Katana™ STML (280.17 ± 83.41-435.95 ± 73.58/3.06 ± 0.27-3.84 ± 0.47) and UTML (258.25 ± 109.98-331.26 ± 56.86/2.35 ± 0.31-2.94 ± 0.33), with no significant differences between layers and layer thicknesses. The range of indications should be carefully considered when selecting the type of monolithic zirconia for fabrication of dental restorations, as materials widely differ in mechanical properties.

Application of Fracture Toughness Understanding to Improve Papermaking Runnability

Runnability of paper is important for increasing the productivity of papermaking, converting, and printing processes. Fracture mechanics theories have been applied to paper for reducing paper breaks and improving their runnability. Fracture toughness has a stronger effect on the paper break phenomenon than tensile strength. Paper breaks when a higher force is applied to paper during the papermaking process than the paper can hold. Efficient methods to improve the toughness of paper will be beneficial to reduce paper breaks. In this study, various factors such as fiber length, intrinsic fiber strength, coarseness, refining, addition ratio of Kraft pulp (KP) related to the fracture toughness of paper were reviewed. Further, the effects of the fiber properties, extent of refining, mixing ratio of KP, recycled fibers and fillers, and moisture content were analyzed. The following were beneficial for increasing the fracture toughness of paper: long fiber length, high intrinsic fiber strength, low fiber coarseness, high refining, high addition ratio of KP for the strengthening effect, low recycling pulp and filler addition ratio, and high moisture content of paper. The mixing ratio of KP had strong effects on improving the fracture toughness whereas the refining effects had weak effects on that. Regarding fiber shapes, straight fibers had a high critical fracture load, whereas curly fibers resulted in a high critical fracture elongation. In the future, detailed research on the fracture toughness of paper is needed, including the dynamic factors, for better understanding of paper breaks during papermaking processes.

Investigation of Properties of the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Me,Al)N Coatings, Where Me Means Cr, Ti, or Mo

The article describes the results of the investigation focused on the properties of the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Me,Al)N coatings, where Me means chromium (Cr), titanium (Ti), or molybdenum (Mo). These coatings have three-layer architecture, including adhesion, transition, and wear-resistant layers, while the latter, in turn, has a nanolayer structure. Despite the fact that the coatings under study have close values of hardness and critical fracture load LC2, there are noticeable differences in wear resistance during the turning of steel. The tools with the coatings under study demonstrated better wear resistance compared to an uncoated tool and the tool with the commercial ZrN coating. The best wear resistance was detected for a tool with the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Ti,Al)N coating. The study of the pattern of cracking in the structure of the coatings has found that, during the cutting process, active cracking occurs in the coating with Cr, which leads to the fracture of the coating, while the process of cracking is noticeably less active in the coatings with Ti or Mo.

An evaluation of the loading condition on mixed-mode stress intensity factors for CTST specimens made of 2024-T351 aluminum alloy

In this paper, the fracture behavior of 2024-T351 aluminum alloy as a key engineering material in the aeronautical industry is investigated under various planar and nonplanar mixed-mode loading conditions involving pure mode-I and pure mode-III loadings. A newly suggested loading setup accompanied by compact tension shearing and tearing (CTST) specimens is utilized to perform fracture tests. Three-dimensional finite element modeling using the interaction integral method is carried out to derive the stress intensity factors (SIFs) and their ratios through the crack front for several mixed-mode configurations. The numerical results reveal that the coupled effect of modes II and III under mixed-mode I/II, I/III and I/II/III loading conditions is remarkable. Moreover, the amounts of SIFs at the center of the specimens are employed to predict the critical fracture loads according to different mixed-mode criteria. Also, scanning electron microscope (SEM) images of the fracture surfaces of CTST specimens are examined to evaluate the effect of different loading angles from a morphological viewpoint. A good consistency can be found among the results of the theoretical solutions of the criteria and the experimental observations for different loading conditions.

Damage mechanisms evolution of TiN/Ti multilayer films with different modulation periods in cyclic impact conditions

The evolution of cyclic impact damage mechanisms ofTiN/Ti multilayer films were investigated in terms of microstructural transformation as the modulation period decreased sharp from micron-scale (1000 nm) to nano-scale (60 nm). It was found that the ductile Ti phases reduced with decreasing modulation period, and the microstructures of films transformed from TiN/TixNy/Ti to TiN/TixNy (x > y). The cyclic impact results showed that both impact resistance and damage mechanisms of TiN/Ti multilayer films were strongly associated with modulation period. In the cyclic nano-impact conditions, the smaller modulation period of TiN/Ti film, the lower critical fracture load and higher fracture probability, thus worse impact resistance. Furthermore, the evolution of cyclic impact damage mechanisms ofTiN/Ti multilayer films were revealed that in T1000 film, only few cracks were observed and the Ti interlayers could prevent cracks from extending deeper into film, resulting in slight fracture with small chippings. While there were many more cracks in T60 film and these cracks could easily across multilayers, leading to severe brittle spalling with multiple layers. It was demonstrated that with the microstructural transformation from TiN/ TixNy/Ti to TiN/ TixNy, a higher cracking probability was found in TiN/Ti films, and the crack propagation mode changed from horizontal along interface to vertical across multilayers.

Phase-field modelling of brittle fracture in thin shell elements based on the MITC4+ approach

We present a phase field based MITC4+ shell element formulation to simulate fracture propagation in thin shell structures. The employed MITC4+ approach renders the element shear- and membrane- locking free, hence providing high-fidelity fracture simulations in planar and curved topologies. To capture the mechanical response under bending-dominated fracture, a crack-driving force description based on the maximum strain energy density through the shell-thickness is considered. Several numerical examples simulating fracture in flat and curved shell structures are presented, and the accuracy of the proposed formulation is examined by comparing the predicted critical fracture loads against analytical estimates.

Fracture characteristics of mixed-mode toughness of dissimilar adherends (cohesive and interfacial fracture)

This paper investigates the fracture behavior of aluminum/polymer dissimilar adhesively bonded joints at different mixed-mode ratios. For this purpose, a series of experiments were carried out using a modified Arcan fixture to obtain critical fracture load in mode I, mode II and mixed-mode, for two types of cohesive and interface starter cracks. Experimental data, along with the Virtual Crack Closure Technique (VCCT) were employed to extract the strain energy release rates. The average values of strain energy release rates were found and for cohesive cracks, and and for interface cracks. Considering the relations between the strain energy release rate and the stress intensity factor, and were also calculated for cohesive and interface starter cracks.