Failure Mode Changes Research Articles

Influence of endodontic irrigants on bond strength between glass-fibre posts and dentin: A systematic review of in vitro studies

Irrigant solutions used during and after endodontic treatment on the dentinal surface can influence the bond strength of glass-fibre posts. The aim of this systematic review was to provide an overview of available scientific evidence on the influence of endodontic irrigants on glass-fibre post bond strength. This review followed the Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines. To identify relevant papers, an electronic search was conducted in PubMed, Cochrane, Elsevier, Scopus and EBSCO databases. There were no language restrictions and the last search was conducted to include studies published up to and including July 1, 2019. We searched for in vitro or ex vivo studies that included human or bovine specimens and reported on dentin-fibre post bond strength with the use of different irrigants for root canals. Common variables were identified to consolidate the data, such as bond strength values, interface failure mode and microstructural changes in the dentin after treatments. From 79 potentially relevant papers identified from the database searches, 19 were included in our study for full-text analysis. Authors of this review independently screened search results, extracted data and assessed the risk of bias. Data heterogeneity was present, with differences in dentin type, bond strength tests and irrigation and luting protocols. Current findings suggest that dentin bonding is adversely affected by 5.25% sodium hypochlorite (NaOCl). Chelators adversely affect bonding to root dentin. Antioxidant agents could recover the bond strength between the glass-fibre post and the dentin. Conditioning with phosphoric acid (H3PO4) and NaOCl/ethylenediaminetetraacetic acid (EDTA) with ultrasonic agitation might be recommended in order to remove the smear layer and produce an adequate resin-tag formation. Ageing affects resin cement-dentin bond strength by degradation of collagen fibrils resulting from the activation of endogenous proteases. Therefore, ethanol (EtOH), chlorhexidine (CHX), or cross-linkers can be used to inhibit the activity of matrix metalloproteinases (MMPs) and maintain bond strength over time to achieve greater and longer-term stability of the bonding interface. There are difficulties in achieving an effective resin-root dentin bond. Therefore, this review is clinically significant because recognising the effects of root canal irrigating substances on the retention of glass-fibre posts is essential to improve the prognosis of endodontically treated tooth restorations.

Fatigue failure and optimization of double-sided weld in orthotropic steel bridge decks

Double-sided weld is an effective way to improve the fatigue performance of orthotropic steel bridge decks (OSBD). However, the fatigue performance and optimization design methods of double-sided welds connecting the U-rib and the deck in OSBD require further study. In this paper, the finite element modeling method suitable for the notch stress approach in double-sided welds is discussed, and its variance from that of the single-sided weld is revealed. All possible fatigue failure modes of double-sided welds, the transfer phenomenon of fatigue crack initiation location and the change of fatigue failure modes under different vehicle loading conditions are revealed. It is further discussed that how the change of the deck plate thickness and the weld foot length alters the fatigue failure mode under the same loading condition. According to the above analysis, in order to obtain the optimal fatigue performance of double-sided welds, an optimal design method based on the fatigue damage factor per unit time under real vehicle loading conditions is proposed. The analysis results show that the fatigue failure modes of the double-sided welds of the U-rib-to-deck welded joint in the OSBD is determined by three factors: loading condition, deck plate thickness and weld foot length. According to the optimization factor proposed in this paper, the thickness of the deck plate and the length of the weld foot can be reasonably determined under different traffic loading conditions, so that the fatigue performance of the rib-to-deck joint in the OSBD is optimized.

Copula-Based Quantification of Probabilistic Dependence Configurations of Material Parameters in Damage Constitutive Modeling of Concrete

The constitutive model of concrete is the key basis for nonlinear analysis of concrete structures under disastrous dynamic actions, e.g., earthquakes. The material parameters of the constitutive model of concrete are essentially probabilistically dependent. However, in practice, it is mostly assumed that these parameters are either independent or perfectly dependent. In the present paper, the quantification of probabilistic dependence configurations between random material parameters and their effects on stochastic structural responses are investigated. Based on the ample amount of data from tested complete curves of compressive stress-strain relationships of concrete with different strength grades, the parameters in the damage constitutive model of concrete are samplewise identified. Further, the probabilistic dependence configurations are studied based on copula theory, which is also considered as a data-mining tool. The complete constitutive curves of concrete are generated according to the obtained dependence configurations and marginal distributions. Then, combined with the probability density evolution method, the stochastic response analysis of concrete structures is carried out. The analysis results show that the dependence among the strength, peak strain, and the parameter of the descendent segment cannot be ignored. Due to the constraint of dependence configurations, the distribution characteristics of the generated point set are substantially consistent with the tested results, and the generated complete stress-strain curves agree well with the tested curves at both the level of sample and the level of second-order moments. In addition, no abnormal complete stress-strain curves, e.g., those with low strength and sharp descendent segment, which are unlikely to occur in the test, are generated. The dependence configuration of the parameters of concrete has considerable effects on the response and reliability of concrete structures, and may even lead to the change of overall structural failure mode. Consequently, ignoring the probabilistic dependence of material parameters may yield misleading results for decision making. Problems to be further studied are also discussed.

Bond strength and bond stress-slip analysis of FRP bar to concrete incorporating environmental durability

Interfacial bond between fibre-reinforced polymer (FRP) composite bars and the surrounding concrete is an important factor in the composite performance of FRP-reinforced concrete beams under load. When exposed to harsh environmental conditions the interfacial bond has been shown in numerous small-scale experimental studies to significantly deteriorate. It is therefore essential that the magnitude of the deterioration is quantified in order for the long-term performance of FRP-reinforced concrete (FRP-RC) members to be determined. In this study, a database consisting of 544 observations of bond strength test results as well as a sub-set database of 315 observations of bond stress-slip results is compiled and statistically analysed in order to quantify reduction factors for both the bond strength and the bond stress-slip behaviour of FRP-RC members. The outcomes of this analysis are further applied to investigate the deterioration required to cause a change in failure mode from bar rupture to bar debonding in order for the deterioration of reinforcement to be considered in reinforcement detailing requirements.

The deformation and failure mechanism of cylindrical shell and square plate with pre-formed holes under blast loading

The deformation and failure mechanism of cylindrical shells and square plate with pre-formed holes under blast loading were investigated numerically by employing the Ansys 17.0 and Ls-Dyna 971. To calibrate the numerical model, the experiments of square plates with pre-formed circle holes were modeled and the numerical results have a good agreement with the experiment data. The calibrated numerical model was used to study the deformation and failure mechanism of cylindrical shells with pre-formed circle holes subjected to blast loading. The structure response and stress field changing process has been divided into four specific stages and the deformation mechanism has been discussed systematically. The local and global deformation curves, degree of damage, change of stress status and failure modes of cylindrical shell and square plate with pre-formed circular holes are obtained, compared and analyzed, it can be concluded as: (1) The transition of tensile stress fields is due to the geometrical characteristic of pre-formed holes and cylindrical shell with arch configuration; (2) The existence of pre-formed holes not only lead to the increasing of stress concentration around the holes, but also release the stress concentration during whole response process; (3) There are three and two kinds of failure modes for square plate and cylindrical shell with pre-formed holes, respectively. and the standoff distance has a key influence on the forming location of the crack initiating point and the locus of crack propagation; (4) The square plate with pre-formed holes has a better performance than cylindrical shell on blast-resistant capability at a smaller standoff distance, while the influence of pre-formed holes on the reduction of blast-resistant capability of square plate is bigger than that of cylindrical shell.

Investigations on cyclic deformation behaviors and corresponding failure modes of a Ni-Based superalloy

High cycle fatigue properties with different stress levels were performed on GH4742 alloy at room temperature (RT) and 750 °C by staircase method. Comparative analyses of failure mode were made at the two different temperatures. The results show that failure mode changes gradually from surface defects failure to interior crystallographic facets failure with increasing temperature. Meanwhile, at 750 °C, the majority of specimens present crystallographic facets failure, while only three of initiations with higher stress level are associated with surface inclusions. The reasons for surface defects initiations are related to local stress concentration under lower temperatures or higher stress levels. The effects of competing failure modes on fatigue properties, including fatigue life and fatigue damage rate, were discussed in detail, which is consistent with the results fitted by Basquin relationship. Transmission Electron Microscope observation reveals that γ′ particles are sheared by dislocations at RT, whereas at 750 °C, climbing, bypassing and shearing mechanisms operate simultaneously, which is due to the higher thermal activation energy and stacking fault energy at 750 °C.

Temperature and structure effects on the impact damage distribution of 3D braided composites

Three-dimensional braided composite materials are prepared by fiber bundle braiding and composite material forming. These materials can realize the integration of material structure to manufacture complex structural parts in a near net-shape way and reduce the number of assembly connections. This material has been widely used in the aerospace industry, high-speed vehicles, and important civil facilities. Computed tomography (CT) and finite element method (FEM) were used to characterize the relationship between the internal damage distribution of 3D braided carbon fiber/epoxy resin composites under multiple transverse impact loading, ambient temperature, and microstructure. It is determined that with an increase in the temperature, the failure mode of resin changes from brittle failure to ductile failure, the interface bond strength decreases, and the failure mode changes to fiber/resin interface cracking and resin debonding. With an increase in the braiding angle, the failure mode changes from interface cracking to resin debonding cracking; interface cracking simultaneously occurs, impact tolerance increases, and local temperature increases with an increase in the absorbed energy. With an increase in the number of impacts, the accumulation of impact damage leads to the clear cumulative effect of reinforcement deformation, interface cracking, and resin debonding.

Computational Micromechanics for the Optimization of Compression Strength of Unidirectional Carbon Fiber Composites for Use in Wind Turbine Blades

As wind turbine blades grow longer, new design parameters gain additional importance such as blade weight, tip deflection and material cost. These parameters require designers to relook at carbon fiber as a potential design solution. However, the composite materials in wind turbine blades are subjected to significant compressive loading, and the compressive strength of carbon fiber reinforced polymer (CFRP) composites is much lower than its tensile strength. This reduction in compression strength is due to a change in failure mode from that seen in tensile loading. The aim of this study is to investigate three factors that affect the compressive failure response of CFRP composites. These factors include fiber defect severity, volume fraction, and multiaxial loading.Compressive strength was shown to have decaying sensitivity with increasing fiber misalignment. Decreasing the volume fraction not only decreased the compressive strength but also increased the compressive failure strain. In addition, adding in-plane shear loads proved detrimental to the compressive load-carrying capacity of a composite structure. This research showed minimizing fiber misalignment in manufacturing processes is only beneficial for high tolerance processes. Decreasing volume fraction could be beneficial for highly flexible structures. Finally, the results demonstrated the need to minimize multiaxial loading for optimal composite compressive response.

The temperature effect on the inter-laminar shear properties and failure mechanism of 3D orthogonal woven composites

Recent increases in the use of carbon fiber reinforced plastics, especially for high-temperature applications, has induced new challenges in evaluating their mechanical properties. The effects of temperature on the shear performance of 3-dimensional orthogonal and 2-dimensional plain woven composites were compared in this study through double-notch shear tests. A scanning electron microscope was employed to investigate the fiber/matrix interface properties to reveal the failure characteristics. The results showed that temperature had a visible impact on the inter-laminar shear strength (ILSS), deformation modes, and failure mechanism. The ILSS decreased as temperature increased, which was caused by the degradation of the matrix properties and fiber/matrix interface properties at high temperature. A finite element model was established to analyze the transient deformation process and the damage mechanism of the 3D orthogonal woven composite. This indicated that Z-binder yarns could improve the delamination resistance of 3D orthogonal woven composites, especially under high temperatures. The changes in failure modes of the 3D orthogonal woven composites was put down to thermal softening of the epoxy resin caused by high temperature and the undulation of the yarns.

Optimization of multi-directional fiber architecture for resistance and ductility of bolted FRP profile joints

In view of the low structural efficiency of bolted joints in pultruded fiber-reinforced polymer (FRP) profiles with mainly unidirectional (UD) fiber architecture, off-axis plies were considered as an effective way to improve bolted joint performance. An experimental study of bolted joints was conducted with laminates composed of UD basalt fiber fabrics laid-up at different ply angles and stacking sequences to optimize the lay-up with regard to the integral structural performance of FRP laminates and bolted joints. Furthermore, 3D finite element models of the joints were established to obtain a better understanding of the progressive joint response and failure. The results showed that laminates with off-axis plies could significantly increase joint resistance due to a shift of the failure mode from sudden shear-out to progressive bearing failure. The change of failure mode thus also changed the response from brittle to pseudo-ductile. The experimental and numerical results agreed well in both the failure mode and joint resistance, with one exception, i.e. the applied Hashin-Rotem failure criterion was not able to capture fiber tie-action resistances in the 90°-plies. An optimum stacking sequence and proportion of 0°-, 45°- and 90°-plies was obtained, which can serve as reference for applications in optimized FRP pultrusion.

Pullout behaviour of ribbed bars in self-compacting concrete with steel fibers

This research mainly focuses on the pullout behaviour of different ribbed bars size embedded in plain Self-Compacting Concrete (SCC) and also in SCC with Steel Fibers (SCCSF). The diameter of the ribbed bars was 12, 16 and 20 mm. The steel fibers used in this study were the hooked end type with 35 mm length and an aspect ratio of 63.6. This study attempts to investigate factors influencing the pullout behaviour by using the embedment length recommended by RILEM RC6 Part 2 which is 5 times the bar diameter using the direct pullout test method. A total of 9 specimens with a dimension of 200 mm cube were prepared and tested. It was found that the proposed embedment length was large for 12 and 20 mm diameter bars but fitting for bond stress investigation with the 16 mm diameter bar. The addition of steel fibers in SCC improves the compressive and tensile strengths of SCCSF and provides concrete confinement that enhances the bond between ribbed bars and the surrounding concrete. Besides, the presence of steel fibers also changes the failure mode of SCCSF specimens especially with 20 mm diameter rebars in which the failure mode changes from premature splitting to pullout.

Mechanical properties and interfacial microstructures of magnetic pulse welding joints with aluminum to zinc-coated steel

In this study, the relations between interfacial microstructure and mechanical behavior of aluminum alloy sheets and zinc-coated steel sheets magnetic pulse welding (MPW) joints were characterized systematically. MPW joints of aluminum alloy and ungalvanized steel sheets were prepared for comparative analysis. Results showed that some of zinc layer on the galvanized steel was washed away to form metal jet under the high-speed collision. The change of failure mode from interfacial failure to base material fracture due to interfacial microstructure evolution was the fundamental reason for different mechanical behavior of two MPW joints. Because of the difference in element content and the severe plastic shear at the interface, the crystalline grain morphologies and sizes of aluminum and zinc in the transition zone changed. Amorphous structure was also found in the transition zone. The existence of the zinc layer would form brittle and hard phases on the interface, resulting in the generation of welding defects, thereby reducing mechanical properties of the joint.

Microtensile properties and failure mechanisms of cortical bone at the lamellar level

Bone features a remarkable combination of toughness and strength which originates from its complex hierarchical structure and motivates its investigation on multiple length scales. Here, in situ microtensile experiments were performed on dry ovine osteonal bone for the first time at the length scale of a single lamella. The micromechanical response was brittle and revealed larger ultimate tensile strength compared to the macroscale (factor of 2.3). Ultimate tensile strength for axial and transverse specimens was 0.35 ± 0.05 GPa and 0.13 ± 0.02 GPa, respectively. A significantly greater strength anisotropy relative to compression was observed (axial to transverse strength ratio of 2.7:1 for tension, 1.3:1 for compression). Fracture surface and transmission electron microscopic analysis suggested that this may be rationalized by a change in failure mode from fibril-matrix interfacial shearing for axial specimens to fibril-matrix debonding in the transverse direction. An improved version of the classic Hashin's composite failure model was applied to describe lamellar bone strength as a function of fibril orientation. Together with our experimental observations, the model suggests that cortical bone strength at the lamellar level is remarkably tolerant to variations of fibrils orientation of about ±30°. This study highlights the importance of investigating bone's hierarchical organization at several length scales for gaining a deeper understanding of its macroscopic fracture behavior. Statement of SignificanceUnderstanding bone deformation and failure behavior at different length scales of its hierarchical structure is fundamental for the improvement of bone fracture prevention, as well as for the development of multifunctional bio-inspired materials combining toughness and strength. The experiments reported in this study shed light on the microtensile properties of dry primary osteonal bone and establish a baseline from which to start further investigations in more physiological conditions. Microtensile specimens were stronger than their macroscopic counterparts by a factor of 2.3. Lamellar bone strength seems remarkably tolerant to variations of the sub-lamellar fibril orientation with respect to the loading direction (±30°). This study underlines the importance of studying bone on all length scales for improving our understanding of bone's macroscopic mechanical response.

High temperature fatigue of heat treated secondary AlSi7Cu3Mg alloys

The high-temperature fatigue behaviour of a heat treated AlSi7Cu3Mg alloy is reported. Fatigue testing has been performed at room and higher temperatures (473 and 573 K) on specimens previously solubilised at 758 K for 24 h and further aged at 453 K for 8 h. Microstructural and fractographic investigations have been used to quantitatively examine the evolution of strengthening precipitates and the different fracture mechanisms. The results show how the fatigue behaviour is comparable in the temperature range between 293 and 473 K. Then, the fatigue strength decreases by increasing the testing temperature from 473 to 573 K. The uniform distribution of fine strengthening precipitates in the α-Al matrix is affected by higher test temperature, which promotes coarsening phenomena of the precipitates. The failure mode changes from brittle to ductile at 573 K.

Reinforced-Concrete Shear Walls Retrofitted Using Weakening and Self-Centering: Numerical Modeling

This paper investigates a novel retrofit strategy for code-deficient reinforced-concrete (RC) shear walls that are vulnerable to undesirable failure modes. The strategy combines weakening by partially cutting the wall base and self-centering by adding post-tensioning. RC walls in need of retrofit were analyzed under lateral cyclic loading using three-dimensional (3D) finite element (FE) modeling. Analyses were validated using test data from the literature on conventional walls that failed in flexure/shear and pure shear. These analyses were used to study the retrofit strategy. A parametric study was conducted to determine the working details of the retrofit method. A method was proposed to select retrofit parameters preliminarily. Retrofitted and original walls were compared. The sequence in which wall components failed was documented to identify changes in failure modes. Results of the analyses showed that although retrofitting reduced energy dissipation capacity, flexural displacements increased due to retrofit of poorly designed RC walls suffering from partial or pure shear failure. Retrofit resulted in fewer cracks, less intense concrete crushing, and a delayed fracture of transverse reinforcement.

Stabilization of sand using different types of short fibers and organic polymer

Due to the loose packing of natural sand, great efforts have been intended to achieve its stabilization and prevent associated engineering failures. As a new soil reinforcement technique, the combined treatment using chemical stabilization and fiber reinforcement has drawn increasing attentions. The focus of this study is to investigate the effect of short fiber types (including polypropylene, basalt and glass fibers) on the mechanical performance of polyurethane (PU) polymer treated sand. Unconfined compressive and tensile tests were performed and analyzed to infer the degree of strength enhancement with different types of fiber reinforcements. Also, intrinsic mechanism and variation in the microstructure were studied by scanning electron microscopy (SEM). The results showed that the strength properties and brittle behaviors were improved greatly by fiber incorporation in comparison with only polymer reinforcement. With same content, polypropylene fiber imparted greater strength to the treated soil due to its well flexible structure and strength properties as compared to other fibers. As observed, 0.8% polypropylene fiber addition led to an increment in compressive and tensile strength by 108.07% and 295.42% respectively, while with same content basalt fiber imparted 63.91% and 147.06%, and fiberglass imparted 47.92% and 253.08% respectively. Additionally, the change in stress-strain curves and failure mode and enhanced value of brittleness index (about 2 to 4 times) indicated increasing ductility. The presence of polymer provided cementation the soil matrix, which also led to great bond strength in grains contacts and fiber-grains contacts. The fibers exhibited stretching and breakage rather than sliding through the soil during failure, which was commonly observed in monofilament polypropylene fiber reinforcement. Soil mechanical properties were also influenced by dry density. As observed, the strength properties got better with increasing dry density while the brittleness became worse, due to enhanced interfacial friction at fiber-sand and sand-sand interface. It was observed that the soil reinforcement with polymer and fiber displayed high strength and modulus for its efficient use being influenced by softness, strength properties, density and size of different fiber types.

Experimental observation and numerical investigation on propagation and coalescence process of multiple flaws in rock-like materials subjected to hydraulic pressure and far-field stress

In this paper, a newly developed rock-like material (cement mortar) was proposed. Multiple flaws (including horizontal and inclined flaws) were prefabricated in the testing specimens, and a number of specimens subjected to hydraulic pressure and far-field stress were performed to study the crack propagation and coalescence process. Experimental results show as following. (1) Under uniaxial compressive condition, the propagation path and direction of preexisting flaws change obviously after the inclined flaws meet the horizontal flaws during the propagation process, and the phenomenon of ‘displacement jumping’ appears. (2) Under biaxial compressive condition, the increase of lateral pressure suppresses the initiation of cracks and secondary cracks at the ends of the inclined flaws. Under the condition of high lateral pressure, these inclined flaws would not propagate through the horizontal flaws and the failure mode changes from splitting to shear failure. The shielding effect of horizontal flaws on stress transfer is gradually increased. (3) Under the combined action of internal water pressure and far-field stress, with the increase of internal water pressure, the maximum principal stress distribution at the tip of wing crack in uniaxial compression gradually decreases, and the initiation stress, initiation angle and peak strength are also gradually reduced. The crack propagation and coalescence laws obtained by numerical simulation based on Continuum-based Discrete Element Method (CDEM) are basically in good agreement with the experimental results. The numerical analysis of the inclined flaws with different internal water pressures penetrating through the horizontal flaws without water pressure is also carried out. With the increase of internal water pressure, the inclined flaws firstly initiates the coplanar crack and then generates the wing crack. When the wing crack propagates though the horizontal flaw, the propagation path also changes. Under the combined action of internal water pressure and far-field stress, the lateral pressure also suppresses the initiation of the wing crack. The increase of internal water pressure weakens the restraint effect of lateral pressure on wing cracks.

Experimental study on the mechanical properties of laminates made of thin carbon fiber plies

Thin carbon-fiber prepregs can improve the designability of the number and the angle of layup at a constant laminate thickness, and meet the requirements of the load bearing capacity of the thin-walled structure. In this work, experiments based on the MIL17 method were performed to investigate the performance of carbon-fiber laminates manufactured from thin prepregs, and compare to those of conventional prepregs. Besides the performance advantages of thin prepregs and conventional prepregs hybrid laminates were explored. It is shown that longitudinal compression properties, tensile properties and mechanical joint properties of the thin unidirectional plates have been improved to some extent. The initial damage strength of the longitudinal tensile of thin laminates is increased by 30%, which indicates that the thin prepregs can delay the generation of initial damage in laminates. It is worth noting that the basic mechanical properties of the hybrid laminates are obviously improved and the longitudinal tensile/compressive strength is approximately increased 50%. In addition, these performance improvements are accompanied by changes in failure modes. The failure modes of thin specimens, especially hybrid specimens, tend to be brittle failure. The results of present study have certain guiding significance for the engineering application of thin prepregs in thin-walled structures.

Influence of elevated temperatures on the bond behaviour between concrete and NSM-CFRP strips

This paper presents an experimental and numerical study about the effects of elevated temperatures on the bond behaviour between concrete and carbon fibre reinforced polymer (CFRP) strips installed according to the near-surface mounted (NSM) technique. In the first part of this study, single-lap shear tests were performed on concrete prisms strengthened with CFRP strips inserted into slits pre-cut in the concrete cover and bonded with an epoxy-based adhesive. The specimens were first heated up to the target temperature (from 20 to 270 °C, measured in the bonding adhesive) and then loaded up to failure. The results obtained show that with increasing temperatures (i) the bond strength is significantly reduced, (ii) the strain distribution along the bonded length becomes closer to linear, and (iii) the failure mode changes from CFRP tensile failure at 20 °C and 50 °C to adhesive failure in the CFRP-adhesive interface at higher temperatures. In the second part of this study, based on the results obtained in the experiments, a numerical procedure was developed to determine the local bond-slip laws at different elevated temperatures. In general, the stiffness and maximum bond stress of the obtained laws decreased with increasing temperatures; in addition, the predicted load vs. slip curves fit well the experimental counterparts.

Üç Nokta Eğilme Yüklemesi Altındaki Düşük Yoğunluklu Polimer Köpük Sandviç Yapıların Hasar Analizi

In this study, low-density polymer foam core sandwich beams, non-existent in the literature, having woven carbon/epoxy face sheets in different core thicknesses and specimen lengths were fabricated and then subjected to three-point bending tests. The bending behavior of the sandwich beams were scrutinized experimentally. The effects of both core thickness and specimen length were revealed. As the ratio of face sheet to core decreases, transferring of shear forces between the face sheets decreases and the face sheets also become weaker. Hence, the failure mode changes from core shearing to indentation and the sandwiches have become tendency to fail by indentation. The theoretical models available in the literature was also utilized to predict the failure mode and collapse forces. The results indicated that both analytical calculations and experimental findings are compatible with each other.