Debonding Resistance Research Articles

Method to improve the bonding strength of polyethylene terephthalate core with glass fiber reinforced skins in a sandwich composite

AbstractComposite materials provide an alternative to conventional structural materials. Sandwich composites show high bending strength and superior strength‐to‐weight ratio. The major drawback in sandwich composites is debonding of skin from core, that causes failure of a component during the usage at different loads. To overcome this issue, the current work identifies a solution of introducing nylon screws (M6 × 32) to adhere firmly the skins consisting of glass fibers with PET (Polyethylene Terephthalate) core. The sandwich composites were fabricated by vacuum infusion process. Two flat sandwich composites were fabricated; one with nylon screws placed perpendicular to the skin and the other a plain sandwich composite. Mechanical characteristics of the specimens such as fracture toughness, flexural strength and shear strength were studied. Specimens with nylon screws showed 21.78% more fracture toughness compared to plain specimen. The presence of screws acts as hindrance to the propagation of cracks in the interfacial region resulting in the enhancement of debonding resistance of the specimens. Also, sandwich specimens with nylon screws exhibited 136% and 142% improvement in flexural and shear strength respectively when compared to plain sandwich specimens. The investigation of scanning electron microscope (SEM) images of tested specimens indicates strong interfacial bonding between skin and the core of specimens with nylon screws.Highlights Introduction of light‐weight nylon screws in z‐direction enhanced the bonding between face sheets and foam core. Sandwich composites with nylon screws exhibited superior bending and shear strength compared to plain specimens. Crack propagation in the interfacial region is restricted by the presence of nylon screws. Investigation of fractured specimens indicated a strong interfacial bonding in the specimens with screws.

Structural Behaviour and Mechanical Characteristics of BlueDeck Profiled Steel Sheeting for Use in Composite Flooring Systems

The BlueDeck profiled steel sheeting system offers an innovative composite flooring solution, integrating high-strength steel sheets with reinforced concrete to form a unified structure. This study aimed to evaluate the development of full composite action, the ultimate bearing capacity, and the flexural stiffness of the system. A comprehensive experimental programme involving 18 four-point bending tests and 6 shear tests was conducted to quantify the mechanical interaction between the steel deck and concrete slab. This study specifically examined bending capacity and vertical deflection, comparing the results with predictions from AS/NZS 2327. It was found that the system consistently achieved full composite action, with composite specimens demonstrating higher flexural stiffness and load-bearing capacity as the concrete depth increased. For example, specimens with 200 mm slab depths exhibited a 60% improvement in ultimate capacity compared to those with 150 mm slabs, while those with 175 mm depths saw a 27% increase. Additionally, the BlueDeck system showed an 81% improvement in de-bonding resistance in thicker slabs. The experimental results exceeded the bending moment and deflection limits prescribed by AS/NZS 2327, confirming that the system is structurally sound for use in buildings. This study provides quantitative evidence supporting the system’s compliance with Australian standards, highlighting its potential for improving construction efficiency through reduced material use, while maintaining structural integrity under imposed loads.

The influence of Zircos-E® etchant, silica coating, and alumina air-particle abrasion on the debonding resistance of endocrowns with three different preparation designs.

The study aimed to evaluate the debonding resistance of three different endocrown designs on molar teeth, using three different zirconia surface pretreatments. Ninety human mandibular first molars were divided into three main groups: endocrowns without ferrule, with 1 mm ferrule, and with 2 mm ferrule. The subgroups were defined by their surface pretreatment method used (n = 15): 50 μm alumina air-particle abrasion, silica coating using 30 μm Cojet™ particles, and Zircos-E® etching. The endocrowns were fabricated using multilayer zirconia ceramic, cemented with self-adhesive resin cement, and subjected to 5000 thermocycles (5-55°C) before debonding. The data obtained were analyzed using a two-way ANOVA. All test specimens survived the thermocyclic aging. The results indicated that both the preparation design and the surface treatment had a significant impact on the resistance to debonding of the endocrowns (p < .001). The 2 mm ferrule followed by the 1 mm ferrule designs exhibited the highest debonding resistance, both were superior to the endocrown without ferrule. Zircos-E® etching and silica coating yielded comparable debonding resistance, which were significantly higher than alumina air-particle abrasion. All endocrowns demonstrated a favorable failure mode. All designs and surface treatments showed high debonding resistance for a single restoration. However, ferrule designs with Zircos-E® etching or silica coating may represent better clinical options compared to the nonferrule design or alumina airborne-particle abrasion. Nonetheless, further research, including fatigue testing and evaluations with different luting agents is recommended.

Preparation technology and experiments of textile lattice sandwich composites

Textile lattice sandwich composite (TLSC) with excellent debonding resistance has been widely investigated. In this paper, the preparation technology of TLSC was improved by foam filling technology, namely hand lay-up and vacuum infusion process, and the flexural properties were studied. The microscope images of TLSC specimens were observed. The structure and resin distribution of TLSC specimens prepared by the above technology was compared. Three-point bending experiments studied the bending properties of foam-filled specimens. The results show that the TLSC specimen prepared by the vacuum infusion process has more resin distribution and high-quality structural form. The obvious resin-rich region appears on the TLSC specimen prepared by hand lay-up. The foam-filling technology can significantly enhance the strength and stiffness of the structure.

Enhancing interfacial shear debonding resistance by mechanical mismatch

Layered systems of similar/dissimilar soft materials are widely used in advanced device applications, including bioelectronics, soft robotics, and energy generators. Device designers strive to minimize the mechanical mismatch between the soft material layers, claiming that the mismatch could be associated with low interfacial debonding resistance and then cause device malfunction. Although strong interfacial bonding has been repeatedly achieved based on the principle of minimizing-mechanical-mismatch, the specific question of whether mechanical matching is the optimal solution for high debonding resistance has never been solidly answered, leaving ambiguity in the further optimization of the layered soft material systems. In this paper, the influence of the stiffness ratio between the soft material layers on the interfacial shear debonding resistance is systematically analyzed through theoretical modeling and finite element simulation approaches. Monotonic improvement of the shear debonding resistance with increasing the loading layer stiffness, even when exceeding that of the substrate layer, is analytically derived by establishing a shear debonding theory of a hyperelastic bilayer. This mechanical-mismatch induced improvement is due to the effective consumption of the external work by the strain energy storage of the loading layer and the large increase in the shear lag length. The theoretical predictions of the debonding resistance agree well with the finite element simulation results, which implies the local non-uniform deformation in the loading and substrate layers near the interfacial crack front causes insignificant influence on the shear debonding. Increasing the modulus or thickness of the loading layer or adding a stiff backing can equivalently improve the shear debonding resistance, which can be quantitatively predicted by the established shear debonding theory. Reasonable applications of the proposed debonding resistance enhancement strategy are also discussed. The findings provide good guidance for the safe service and further optimization of the layered soft material systems to improve the device reliability.

Survival and debonding resistance of posterior cantilever resin-bonded fixed dental prostheses for moderately and severely worn dentition during thermomechanical loading.

The purpose of this study was to investigate the survival rate, the debonding resistance, and the failure modes of different occlusal veneer designs when used as a retainer for posterior cantilever, resin-bonded fixed dental prostheses (RBFDPs) at two tooth wear levels. Four test groups were assigned: two groups with occlusal-proximal preparation (PT1 and PT2 for grade 2 and 3 wear), and two groups for occlusal-proximal and lingual preparation (PLT1 and PLT2 for grade 2 and 3 wear) Monolithic zirconia ceramic (3Y-TZP) RBFDPs were luted with an adhesive bonding system (Panavia V5). The specimens underwent a chewing simulation for 1.200.000 cycles with a load of 5kg and thermocycling for 7500 cycles between 5°C and 55°C. The surviving restorations were debonded under quasi-static conditions. The results were analyzed with ANOVA. The specimens exhibited a 100 % survival rate after thermomechanical fatigue loading. The debonding resistance was statistically significant higher for group PLT1 than for group PT1 (P=0.004), and higher for group PT2 than group PT1 (P≤0.001). However, the debonding resistance showed no statistically significant difference between groups PT2 and PLT2 (P=0.343), and groups PLT1 and PLT2 (P=0.222). Groups PT1 and PT2 showed favorable failure modes in 62.5 % and 0.00 % of the specimens, respectively. While groups PLT1 and PLT2 presented 25 % favorable failure modes. Occlusal veneers showed promising results as a retainer for cantilever RBFDPs. The lingual extension might increase debonding resistance. Nevertheless, conservative designs with lingual and proximal bevels are to be recommended, irrespective of the level of tooth wear.

Temperature-Dependent Debonding Resistance of 316 Stainless Steel, Inconel 625, and Ti-6AL-4V Alloys

This study investigates the temperature-dependent debonding properties of 316 Stainless Steel (SS), Inconel 625, and Ti-6Al-4V alloys in additive manufacturing using the finite element method. The analysis reveals notable relations between in mechanical properties and debonding resistance among these materials. Inconel 625 demonstrates superior performance at elevated temperatures, while SS and Ti-6Al-4V alloys show earlier degradation. Regarding debonding resistance, Inconel 625 performs comparably to SS and Ti-6Al-4V alloys, with Ti-6Al-4V exhibiting consistent resistance below 500 °C. SS, however, experiences a rapid loss of debonding resistance at lower temperatures. These findings provide valuable insights for material selection and design optimization in additive manufacturing. Further research can expand our understanding of these materials' behavior under different temperature regimes using the finite element method, enhancing their application potential.

The biomechanical role of the functionally graded microfibrils in the wood cell wall

The cellulose microfibril in the wood cell wall possesses a functionally graded structure, the biomechanical contribution of which is unclear. At the molecular scale, we analyze the heterogeneous crystallinity of the microfibril and characterize its stiffness gradient with the help of molecular dynamics. The determined stiffness profile is then upscaled to the cell wall level, based on which a shear-lag analytical model is developed to reveal the load transfer mechanism in the cell wall. We find that the presence of the stiffness gradient can significantly alleviate the stress concentration on the interface by reducing the interfacial shear stress up to 70%. The analysis on the debonding procedure shows profoundly enhanced debonding resistance of the cell wall due to the graded structure. Moreover, we identify a novel “dual debonding” mode, meaning that the debonding initiates and propagates in both the edge and inner regions of the interface until the two debonded regions join each other, which is much more complex than the edge debonding mode exhibited by the conventional fiber-reinforced composites. The stress alleviating effect, together with the special debonding mode, profoundly postpones the interfacial debonding of the material, leading to a significantly enhanced debonding resistance. A discussion on the structural profile of the microfibril shows that the special “dual debonding” mode can only be achieved with specific stiffness gradients. In all, we believe our work helps to unravel the biomechanical role of the microfibril in the wood cell wall, and builds the theoretical foundation for tailoring the bio-inspired composites reinforced by functionally graded fibers.

Enhanced flexural properties of bionic carbon fiber sandwiches inspired by the coconut shell

Carbon fiber reinforced plastics (CFRP)/metal foam sandwiches with high strength-to-weight ratios are in growing demand for applications in architecture, automobile, and aerospace. However, most of the sandwiches have low mechanical properties due to the weak metal foam cores and the low interfacial bond strength between cores and skins. In this study, inspired by the natural coconut shell, novel sandwich structures containing magnesium syntactic foam (MSF) cores were designed to improve flexural properties. The CFRP skins were selected to mimic the high strength and multilayer structure of the exocarp and mesocarp, and two types of MSF cores (PMSF with low density and SMSF with high density) were used to mimic the hierarchical cellular structure of the endocarp. The cores with different structures will significantly affect the failure mechanisms and flexural properties of the corresponding sandwich structures. Compared with conventional CFRP/MF, the peak load and flexural stiffness of bionic CFRP/PMSF and CFRP/SMSF are significantly improved due to the hierarchical cellular structure of MSF cores. The enhanced skin-core debonding resistance allows bionic CFRP/PMSF to have better structural integrity under bending loads. Therefore, the CFRP/PMSF exhibits the highest specific flexural strength and specific energy absorption capacity, though the PMSF core has the lowest specific flexural properties. This result confirms that the reasonable matching between the PMSF core and the CFRP skin transfers the load more effectively and improves the strength-to-weight ratio of the sandwich structure. The proposed bio-inspired design method is expected to supply an effective way to enhance the mechanical properties of conventional CFRP/MF sandwich structures in a wide range of engineering applications.

Experimental study on the flexural strengthening of one-way RC slabs with end-buckled and/or externally bonded CFRP sheets

Reinforced concrete (RC) slabs are widely strengthened in flexure by externally bonding (EB) carbon-fiber-reinforced polymer (CFRP) sheets, where debonding failure remains a critical issue. To solve the debonding problems, a self-locking device is initially proposed to enhance the anchorage at the end of FRP sheets for strengthening of RC slabs in this study. The effects on the debonding resistance and the improvement of the strengthening efficiency are experimentally investigated. Six one-way RC slabs strengthened with end-buckled and/or externally bonded CFRP sheets were prepared for the four-point bending tests. All strengthened specimens had higher ultimate loads than the reference specimen. While the slab strengthened by EB CFRP had a limited increase in ultimate load, the improvement was significant for the cases with hybrid anchored (HA) CFRP including both end-anchorage and external bonding, which was 46.2%. In this case, the interfacial stresses could be reduced and the end debonding can be avoided due to the increasingly tight anchoring effect, and the ultimate load can be increased even after partial debonding since the stress can continue to be transferred via mechanical anchorage. When the specimens were strengthened with HA CFRP, the surface treatment had a marginal influence on the strengthening effect. The strength of the slabs strengthened with HA CFRP decreased with the length of CFRP sheets, which is contrary to the trend of cases using EB CFRP. Finally, expressions were proposed to estimate the strain of the CFRP and load-carrying capacity of the strengthened members at the ultimate state, and the test results were within the range of the calculated results.

Using end buckles to improve debonding resistance in FRP-bonded precracked RC beams

The strengthening effect of reinforced concrete (RC) members externally bonded (EB) with fiber reinforced polymer (FRP) laminates is significantly affected by interfacial debonding failure. To improve the connection between FRP sheets and concrete, a novel type of anchor device for FRP sheets called buckle was proposed in this study. This device can effectively lock the end of the sheet using a patented method of wrapping. In addition to conventional external bonding, bolts were installed on the buckles to form hybrid anchored (HA) FRP sheet. To verify the effectiveness of this new method, a precracked RC beam was prepared in comparison with two undamaged beams strengthened with EB or HA FRP sheets. As observed, end buckles can limit the development of cracks regardless of initial cracking. Despite the occurrence of intermediate debonding due to initial cracks, both the ultimate capacity and failure ductility were significantly improved. Owing to the end buckles, the debonding resistance was excellent, and the initial cracking of the beam hardly affected the strengthening effect. In addition, existing formulas were used to calculate the lower limit of the ultimate load of the specimen strengthened with HA FRP, which was still higher than that of the specimen strengthened by EB FRP. Therefore, the results confirmed that the debonding resistance was greatly enhanced due to the locking of the FRP sheet via end buckles, and the proposed method is useful to guarantee the strengthening effect.

Double-layer woven lattice truss sandwich composite for multifunctional application: Design, manufacture and characterization

Woven lattice truss sandwich (WLTS) structures have excellent debonding resistance with integral textile construction. As the WLTS has limited thickness, a double-layer WLTS (DWLTS) composite was designed and fabricated to improve the blast resistance of the sandwich panel, as well as keep its electromagnetic (EM) wave transmission properties. The panel was placed by two layers of WLTSs and plain fabrics, and co-cured using vacuum bag molding process to ensure the interfacial shear resistance. In-field explosion experiments reveal that the DWLTS has excellent blast-resistance and EM wave transmission characteristics. The transmission exceeds 80% in 4.5–8.5 GHz and 16–17.2 GHz, and the maximum transmittance is 98.27% at 4.9 GHz. The panel has little damage until the scaled distance is smaller than 1.026 kg/m1/3 with standoff distance of 0.6 m and TNT mass of 0.2 kg. No debonding was observed.

Development and implementation of a simultaneous fatigue crack growth test setup for polymeric hybrid laminates

Delamination is a common and highly relevant in-service failure mode of laminated structures. Cyclic mechanical loads superimposed with environmental factors, such as hot-humid air, are most critical. To evaluate the cyclic debonding resistance of polymeric hybrid laminates, fracture mechanics approaches based on double cantilever beam (DCB) specimens are well established. However, conventional fatigue test setups allow for measurement of just one specimen which is rather time consuming. The main objective of this paper was to develop and implement a novel fatigue test setup for simultaneous characterization of multiple DCB specimens. To validate the simultaneous fatigue testing system, steel/epoxy laminates of different number of steel plies and epoxy adhesive layers with or without filler were characterized using the novel fatigue test setup and a conventional electrodynamic test machine. Fatigue crack growth data was fitted by a form of the Hartman-Schijve crack growth equation. To derive a statistically significant threshold value a fitting procedure was employed. A good agreement of the crack growth kinetics data at ambient conditions was obtained confirming the high quality and reliability of the novel simultaneous fatigue test setup. Moreover, reliable data were gathered at the beginning of the displacement–controlled experiments in the instable crack propagation regime, as the displacement amplitude was reached from the first cycle onward. The novel test methodology is of special relevance for development and screening of adhesive formulations.

Ultra-high compressive strength of 3D woven spacer composites with bulked glass fiber and saturated resin absorption

Three-dimensional woven spacer composites (3DWSCs) have a great potential to applied in aerospace or transportation fields due to their high strength-to-weight and stiffness-to-weight ratios, with excellent skin-core debonding resistance. Among these properties, the compressive strength of the 3DWSCs which is most critical, and still needs to be improved to meet the highly requirements in practical applications. In this study, we designed and manufactured 3DWSCs with highly enhanced compressive strength and energy absorption by adopting bulked glass fibers (BGFs) as pile yarns to weave its core layer to absorb more epoxy resin. Consequently, the specific compressive strength of 3DWSCs woven by BGFs as pile yarns with saturated epoxy resin absorption was 52.54 MPa g−1 cm3, 180% higher than that of the 3DWSCs woven by regular glass fiber (RGFs). Furthermore, the work of fracture of 3DWSCs woven by BGFs as pile yarns with saturated epoxy resin absorption was 14.82 N m, which enhanced 474% compared with that of 3DWSCs woven by RGFs. The failure cross sections depicted multiple brittle fractures of the pile yarns for both composites under compression, which caused multiple peaks in their stress–strain curves.

Influence of nonwoven interleave layer on interlaminar fracture of sandwich-structured composites

Debonding between the skins and the core is one of the critical failure modes encountered by sandwich-structured composites in highly strained conditions. The onset and growth of a debond critically hinder the load-bearing capacity of the sandwich structure. This paper investigates the effect on the debonding resistance of a sandwich-structured composite by the addition of nonwoven flax interleave veil in the skin-core interface. Mode-II fracture toughness is estimated through a proposed method based on curve fitting of numerical data to experimental results. Experimental data are obtained in a four-point bending test following the standard DIN 53 293 and Cohesive Zone Modelling (CZM) is implemented as the numerical tool in the analysis of Mode-II skin-core debonding. A series of sandwich specimens are fabricated using twill weave e-glass fabric and expanded polystyrene core with and without the addition of an interleave layer. Numerical data show a 60 % increment in Mode-II fracture toughness with the inclusion of a flax interleaf layer. Microscopic images attribute the increment to the presence of fibre bridging effect. The proposed method produces a good fit of numerical data to experimental results.

Mechanical and thermal shock properties of Cf/SiBCN composite: Effect of sintering densification and fiber coating

AbstractIn this work, resin‐derived carbon coating was prepared on carbon fibers by polymer impregnation pyrolysis method, then silicoboron carbonitride powder was prepared by mechanical alloying, and finally carbon fiber‐reinforced silicoboron carbonitride composites were prepared by hot‐pressing process. The effects of sintering densification and fiber coating on microstructure, mechanical properties, thermal shock resistance, and failure mechanisms of the composites were studied. Fiber bridging hinders the sintering densification, causing more defects in fiber‐dense area and lower strength. However, higher sintering temperature (1800–2000°C) can improve mechanical properties significantly, including bending strength, vickers hardness, and elastic module, because further sintering densification enhances matrix strength and fiber/matrix bonding strength, while the change of fracture toughness is not obvious (2.24–2.38 MPa·m1/2) due to counteraction of higher debonding resistance and less pull‐out length. However, fiber coating improves fracture toughness greatly via protecting carbon fibers from chemical corrosion and damage of thermal stress and external stress. Due to lower coefficient of thermal expansion, lower fiber loading ratio, less stress concentration at the fiber/matrix interface, and better defect healing effect, lower sintering temperature favors thermal shock resistance of composites, and thermal shock recession mechanisms are the damage of interface.

Static and Fatigue Debond Resistance between the Composite Facesheet and Al Cores under Mode-1 in Sandwich Beams

The debonding toughness between unidirectional glass fiber reinforced polymer face sheets and cellularic cores of sandwich structures is experimentally measured under static and fatigue loading conditions. The effect of various core geometries, such as regular honeycomb and closed-cell foams of two relative densities on the adhesive interfacial toughness is explored using the single cantilever beam (SCB) testing method. The steady-state crack growth measurements are used to plot the Paris curves. The uniformity of adhesive filleting and the crack path was found to affect the interfacial toughness. The static Mode-1 interfacial toughness of high-density foam cores was witnessed to be maximal, followed by low-density honeycomb, high-density honeycomb, and low-density foam core. Similarly, the fatigue behavior of the low-density honeycomb core has the lowest crack growth rates compared to the other samples, primarily due to uniform adhesive filleting.

Investigating the effect of steel fiber content on bond behavior between externally bonded CFRP-to-concrete joints

A number of studies have identified interfacial debonding as a major challenge in externally bonded FRP strengthened systems. The addition of steel fiber into concrete enhances the debonding resistance, ductility and subsequently increase the strength of FRP laminate-concrete interface. The main purpose of this experiment is to explore the incorporation of different steel fiber contents in the interfacial bond between CFRP laminates and concrete substrate. Five groups of the double shear specimens were fabricated with hooked-end short steel fibers having five different volume contents namely; 0, 0.25%, 0.5%, 1.0%, and 1.5%. The impact of different fiber volume content on the maximum shear stress, slip at maximum shear stress and interfacial bond stress-slip relationship were analyzed. Results showed specimens with 0.25%–1.5% short steel fibers improved their maximum shear stress considerably over the control specimens. The failure modes of specimens were debonding in concrete substrate and concrete shear failure. Finally, an analytical interfacial bond-slip model considering the influence of volume fraction of short steel fibers is proposed.

Experimental investigation of stirrup confinement effects on bond-slip responses for corner and middle bars

Stirrup confinement on bond between concrete and reinforcement is vital for RC (reinforced concrete) structures as it strengthens the friction and mechanical interlock between the two kinds of materials. In this paper, an experimental study has been carried out to look into the stirrup effects on bond-slip responses of RC with corner embedded reinforcing bars and bars embedded in the middle area of cover (corner and middle bars). This aims to quantify the difference of the bond strength caused by the embedment position of reinforcement while confined with hooked and straight stirrups. Different material properties have also been considered in the experiment including concrete cover, bar diameter and stirrup diameter. The failure modes for different specimen groups are presented and discussed. Besides, the influence of stirrup confinement effects on global load-slip response is also investigated by conducting another experiment with long embedment length of reinforcing bars which also includes the corner bars and middle bars. Furthermore, the debonding resistance compared with yielding force of the reinforcing bars are compared and analyzed for the global load-slip responses with stirrup confinements.

Fracture behavior of restored teeth and cavity shape optimization: Numerical and experimental investigation

ObjectivesSince restored teeth are subject to more damages than intact teeth, investigating their fracture behavior is important. However, so far, improvement of the debonding behavior of the restoration and fracture of restored teeth considering the geometry of the restoration and different restorative materials has remained understudied. The aim of this paper is to numerically and experimentally investigate the debonding behavior of the restoration in premolar teeth in order to reduce the stress of restoration thereby reducing the mechanical failure. Methodsthe fracture test for intact and Standard Class-II Mesial–Occlusal–Distal (MOD) restoration premolar teeth restored with several types of composite and conventional adhesive was performed in order to investigate their fracture behavior. The mechanical properties and fracture of composites as well as the adhesives used in experimental tests were obtained through separate standard mechanical tests. In addition, a number of composites and other adhesives were also chosen from other references, and by numerically simulating the fracture process of intact teeth and those restored with the materials of interest, the fracture behavior and yield load limit were investigated and predicted for them. Next, in order to reduce the stresses of bonding region and improve the damage behavior, using the stress-induced material transformation (SMT) optimization algorithm applied as code in finite element (FE) software, the shape of the restoration has been optimized based on different restorative materials. In order to confirm the numerical results, the fracture tests of teeth samples were performed with conventional and optimized restoration forms. Furthermore, using scanning electron microscopy (SEM) method, the fracture surface of the tested samples was examined. Resultssince the fracture behavior of teeth restored with different materials is different, the optimized MOD restoration would be also different for each of these restorative materials. By selecting TU-shape for the restoration in each of the samples, the debonding resistance and final fracture of teeth compared to the MOD restoration increased 51% in Pd and 11% in Pf for numerical results and 40% in Pd and 4% in Pf for experimental results. The obtained results suggest that choosing a proper shape for the restoration based on the properties of restorative materials leads to diminished normal and shear stresses and enhanced debonding resistance. Also, the yield load limit of the defective teeth would also improve considerably. SignificanceThe clinical importance of this study is to predict strength of restored teeth and cavity shape optimization under variable conditions. Also, this paper introduces effective parameters on strength reduction/enhancement to dentists.