Debonding Failure Research Articles

Flexural Strengthening of Reinforced Concrete Beams with Variable Compressive Strength Using Near-Surface Mounted Carbon-Fiber-Reinforced Polymer Strips [NSM-CFRP

An experimental and analytical investigation was conducted on reinforced concrete (RC) beams strengthened in flexure using the near-surface mounted carbon-fiber-reinforced polymers (NSM-CFRPs) technique. A total of 11 full-scale RC rectangular beams were cast and tested under a monotonic three-point bending test, up to failure. The main test variables adopted in this study were the concrete compressive strength (high, medium, and low), the number of CFRP strips, and the strip length. The results indicated that the use of NSM-CFRPs strips in different configurations efficiently increased the load-carrying capacity of the strengthened RC beams, in which all these beams exhibited a higher moment resistance than the corresponding un-strengthened beam. Results also showed that all strengthening schemes were successful in increasing the flexural capacity of the specimens tested. Such increases ranged between 10.36% and 52.28%. Notably, a significant improvement in the ultimate load ratio was observed with beams having a low compressive strength of 17-MPa, then followed by the beams with medium strength (32-MPa), and finally beams with high compressive strength (47-MPa). The NSM technique reduced the occurrence possibility of the CFRP de-bonding failure mode. Furthermore, the test results were compared with theoretical predictions using the ACI 440.2R17 guidelines and showed a good agreement between these results.

Interfacial behavior of externally bonded BFRP-to-concrete joints using different epoxy adhesives

The purpose of this study is to investigate the influence of adhesive types on the interfacial behavior of externally bonded basalt fiber reinforced polymer (BFRP) sheet-concrete substrate. Twelve manufactured double-lap shear samples were tested using four bonding adhesives. The strains on the surface of BFRP‐concrete joint were determined using electrical resistance strain gauge together with two‐dimensional digital image correlation technique (2D‐DIC). Experimental results show that properties of different bonding adhesives i.e., stiff (linear elastic, higher strength) and soft (nonlinear elastic, lower modulus, higher ultimate strain) has a significant impact on the failure mode, stiffness, ultimate load, strain and shear stress distribution nonetheless not so much on bond-slip relationship. The failure modes of specimens changed from interfacial debonding or cohesive failure in concrete substrate for stiff adhesive specimens to debonding in adhesive layer when soft adhesives are used. Stiff adhesive interfaces experienced higher ultimate loads from 1.1 to 1.3 times higher than soft adhesive interface. Meanwhile soft adhesives are shown to possess a lower maximum shear stress, higher interfacial fracture energy and longer stress transfer length.

Numerical Studies on Failure Mechanisms of All-Composite Sandwich Structure with Honeycomb Core under Compression and Impact Loading Conditions.

The all-composite sandwich structure with the honeycomb core is a lightweight and high-strength structure with broad application scenarios. The face sheet and honeycomb core of the proposed all-composite sandwich structure in this work are composed of carbon-fiber-reinforced polymer (CFRP) composites. The mechanical response and damage mechanism of the all-composite sandwich structure under out-of-plane quasi-static compression and out-of-plane impact are studied by numerical methods. The refined finite element models of the sandwich structures are built on the ABAQUS/Explicit platform. The micromechanics of failure (MMF) theory based on physical component failure is used to describe the intralaminar damage mechanism of the face sheet and honeycomb core, and the mixed-mode exponential cohesive zone model (ECZM) is utilized to simulate the initiation and evolution of interlayer damage. In addition, the cohesive contact approach is adopted to capture the debonding failure at the face-sheet/core. The numerical results show that the all-composite sandwich structure has the characteristics of large structural stiffness and strong energy absorption ability. The failure mechanism of the all-composite sandwich structure under compression is mainly matrix damage and delamination of the honeycomb core, with buckling and folding in appearance. Under out-of-plane impact, matrix damage and delamination arise on the upper sheet, little damage is observed on the lower sheet, and the delamination damage morphology tends to be circular with increasing impact energy. In addition, the interface failure of the upper-sheet/core is more than that of the lower-sheet/core. In addition, the matrix damage near the impact center of the honeycomb core tends to be consistent with the delamination contour, and a small amount of fiber failure is also observed, which manifests as a collapse morphology of the impact area. The research results enrich the understanding of the mechanical behavior of all-composite sandwich structures with honeycomb cores and provide theoretical support for their potential applications.

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

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

Improving the flexural behavior of RC beams strengthening by near-surface mounting

Abstract This article presents the experimental investigations undertaken to evaluate the strengthening and enhancement characteristics of near-surface mounted (NSM) devices using different types of bars. A total of 4 concrete beams (150 mm × 300 mm × 1,500 mm) were reinforced in flexure. Three beams strengthened with different embedments of NSM (carbon fiber-reinforced polymer [CFRP], Glass fiber-reinforced polymer [GFRP], and steel) bars, and one unstrengthened beam used as a control beam were tested under monotonic static loading to determine the enhancing influence of the fiber-reinforced polymer (FRP) reinforcement. The performance of different bars used to establish the concrete is examined. A general methodology to evaluate the improving flexural behavior of RC beams strengthened with NSM–FRP bars is presented. A quantitative criterion governing debonding failure is established. The proposed bond model assumes linear elastic behavior for the concrete, adhesive, and NSM–FRP bars, following the same philosophy as the American concrete institute [ACI] provisions for bond analysis and design to control the cracks. So FRP reinforcements show substantial deformation before failure when the cross-sectional area is based on a permissible strain during service, so there is no need to check the deformability. The results of the tests show that using NSM–CFRP bars improves the flexural capacity and stiffness of the strengthened concrete beams of other types.

Numerical modelling of ultrasonic guided waves for detection and characterization of debonds in FRP strengthened beams

Debonding failure in fibre reinforced polymer (FRP) strengthened structures is one of the most critical modes of failure. Timely detection of the debonds are vital for the safety of the structure. This study compares the three numerical models of ultrasonic guided wave generation in FRP strengthened concrete beam in an effort to detect and characterize debonds at the concrete-FRP interface. Numerical models of a carbon reinforced polymer (CFRP) strengthened beam with debonds of different sizes are prepared using commercially available finite element (FE) software ABAQUS®. The ultrasonic guided waves are introduced in the beam by the application of narrowband transient vertical and in-plane surface excitations representing contact type and surface bonded piezoelectric (PZT) transducers, respectively. A new model of angle beam transducer is also proposed, aiming to generate a particular guided wave mode in the CFRP strengthened beam. The wedge angle of the transducer is chosen in accordance with Snell’s law so that the desired mode is propagated in the beam. To prevent the reflections within the transducer, infinite elements are used for modelling the transducer boundary. Moreover, to minimise the computational cost, infinite elements are also used in the beam side faces. The models are validated by comparing the group velocity with the velocity obtained by the dispersion curve. Later, extensive parametric studies are conducted with the aim to relate the wave propagation characteristics to the debond sizes. It is found out that the amplitude of hilbert transform of the scattered wave increases with the increase in debond. size.

Correlation between solid propellant failure and interface debonding in solid rocket motors

In the traditional integrity analysis of solid rocket motors, solid propellants failure and propellant-liner interface debonding were intentionally differentiated. This empirical distinction of failure regions based on the macroscopic phenomenon neglects their physical correlation, consequently increasing both experiment quantity and simulation complexity. Here, by experiments and simulations, propellant-liner interface debonding is shown to be induced by propellant breakage, i.e., the substrate failure. In experiments, interface debonding and propellants failure share the same cavitation and stringing processes in crack initiation, and the measured break strain of solid propellants and fracture energy of interface satisfy a similar temperature/strain-rate dependent shifting phenomenon. The finite element model can well predict both the strain field and the stress-strain response of interface debonding by using the parameters calibrated by tensile tests of solid propellants, verifying that interface debonding is induced by propellants breakage. Overall, failure envelopes of both propellants and interfaces satisfy a similar peak-position shifting phenomenon but different peak-value shifting phenomena. The time-temperature superposition of HTPB polymer binders induces the peak-position shift, and strain concentration and relaxation of propellants in the crack front induce the peak-value evolution. This study is promising to unify and simplify the solid propellants failure and interface debonding in the integrity analysis.

Mechanical properties of adhesive interface for the expandable packer rubber with nylon 66 cord under high pressure and high temperature

In this paper, the expandable packer rubber with nylon 66 cord was selected as research object. By carrying out a single pull-out experiment of nylon 66 cord rubber, it was gotten that the critical failure energy of the adhesive interface between the cord and the rubber matrix was 3.21 kJ/m2. The Cohesive Zone Model (CZM) was used to describe the bonding state of interface between nylon cord and rubber matrix and the debonding failure criterion was then established for the adhesive interface between nylon 66 cord and rubber matrix. The mechanical properties and working performance were analyzed systematically for the expandable packer rubber under different pressures and well temperatures. The results showed that:1) When the fracturing pump pressure was 50 MPa∼80 MPa, the shear stress of the packer rubber matrix was less than the allowable shear stress of 17.5 MPa, and the matrix didn't appear shear tearing damage. So the packer rubber filled with nylon cord could effectively protect the rubber matrix and avoid shear tear damage. 2) When the fracturing pump pressure was 80 MPa, the interface failure energy of the lower rubber was greater than the critical failure energy of 3.21 kJ/m2, and the interface debonding failure occurred between cord and matrix. 3) When the well temperature was 25 °C–175 °C, the shear stress of the rubber matrix increased with the increase of well temperature, but he maximum shear stress of the matrix was less than the allowable shear stress of 17.5 MPa. The failure energy of the adhesive interface was less than the critical failure energy of 3.21 kJ/m2. So there was no shear tear on the matrix of the rubber and the adhesive interface was well bonded. Therefore, the expandable packer rubber with nylon 66 cord could work well in a higher well temperature environment. It is concluded that the research results can provide theoretical guidance for exploring the performance of the expandable packer rubber with nylon cord.

Analysis methodology for the assessment of unvented honeycomb sandwich structures subject to in-plane and pressure loads

As an aircraft or spacecraft ascends, the atmospheric pressure drops. If the internal pressure is not released, a pressure differential develops on the facesheet. With an in-plane load from vehicle acceleration as well, the pressure and in-plane load may cause failure. Vented sandwich structures are strongly preferred since they release the internal pressure; however, special cases still require an unvented design. This paper provides an analysis and test methodology for unvented sandwich structures. Parametric studies of facesheet-core debonding and buckling were conducted via finite element analysis, considering geometric, material, and load parameters. Design curves based on the key nondimensional parameters were tuned to the data from the parametric study, providing a tool to predict facesheet-core debond failure. Examples of how to use the design curves in practical applications are provided.

Structural integrity evaluation of cyclic loading Glass Fibre Reinforced Polymer composite by acoustic emission and heat transfer

GFRP composites experience structural changes like matrix cracking, debonding, delamination, and fibre failure on static and dynamic loading. In this work, composites with varying fibre orientation interaction angle and volume fractions are prepared and exposed to cyclic load. The cyclic load (R = 0) is a constant amplitude flexural load imposed on the cantilever beam specimen with varying frequencies (2.6, 4.6, 8.6 Hz) and cycles (up to 44 × 103). The structural integrity of the specimens on loading is examined in terms of Flexural, modulus, Acoustic Emission (AE) and heat transfer changes. The drop in flexural modulus is minimum in higher Vf = 32% laminate (A1 = 7.01%, B1 = 1.86%) than the lower Vf = 25% (A2 = 19.86%, B2 = 8.6%). The observed AE peak frequency for the induced damages is in the range of 50–100, 110–230, 245–380 kHz. The drop-in fibre volume fraction has a significant role in laminate with lower fibre interaction (Type A) to offer minimum variation (5.25%) in AE activity count which is the opposite in laminates with higher fibre interaction angle (31.75%). The step heat thermography exhibits minimum temperature difference (∆T) for moderate loading frequency and in a few cases, ∆T drops well below the virgin, insisting on in situ thermography to study the dynamic changes in composites. A fibre dominant behaviour can be observed with minimum variation in AE activity in a lower fibre interaction angle. Thus, the fibre orientation angle and fibre volume fraction have a significant role in the retention of the structural integrity of composites in dynamic loading.

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.

Study on a Transparent Similar Rock-Anchoring Structure under Impact Tests and Numerical Simulation Tests

Interface slip is one of the main failure forms of an anchor structure, but the debonding slip process of rockbolt cannot be directly observed under impact load, so it is important to study the failure mechanism of the interface debonding of an anchor structure. For this purpose, a kind of transparent similar rock-anchoring structure and a new rockbolt impact load test system were developed. The debonding process of the anchor structure was carried out based on the system and Particle Flow Code (PFC) simulation test. The main conclusions are as follows: Axial force of rockbolt decreases progressively from the load end to the other end, but the shear stress of the interfaces increases at the early stage and then decreases. The majority of shear stress is at I interface compared to shear stress at II interface. The crack in the transparent sample occurs first in the middle of the sample, then extends to the local position of the two interfaces and finally penetrates all cracks, and the debonding failure mode is dual-interface mixed. According to laboratory tests and PFC simulation tests, the crack growth process can be divided into three stages. The results of the PFC simulation tests are similar to those of the laboratory impact tests of rockbolt.

Experimental investigation into the synergetic damage of foam-filled and unfilled corrugated core hybrid sandwich panels under combined blast and fragment loading

Foam filling strategy has been demonstrated to owing the ability to improve the blast resistance of sandwich panels under bare blast loading. But it is unclear that the effect of foam filling for performance improvement of sandwich panels in response to combined blast and fragments loading. In this paper, the corrugated core sandwich panels with and without aluminum foam fillers were designed, fabricated and finally tested under combined blast loading. Main attention focused on the influence of stand-off distance, foam filler density and core configuration on the dynamic responses in terms of deformation modes and failure mechanisms. The perforation failure of target panels could be alleviated with the increase of stand-off distance. The increase of foam filler density hardly affected the deformation/failure modes of panels, but it could reduce the permanent deformation of core webs and front face sheet. Relative to unfilled sandwich panels, foam filling behavior is an effective way to relieve the debonding failure between face sheet and core webs. Overall, the performance of foam-filled sandwich panels under combined blast loading is mediocre. The failure mode of foam-filled sandwich panels would transform from localized plastic deformation mode under bare blast loading to catastrophic failure under combined blast loading.

Numerical performance evaluation of debonding strength in fiber reinforced polymer composites using three hybrid intelligent models

Debonding of the fiber-reinforced polymer (FRP) reinforcement is considered as a significant issue in the concrete design because of shear stresses. The main problem is the potential of brittle debonding failures that can highly reduce the effectiveness of strengthening. Shear bond strength and the governing variables have been empirically analyzed several times; however, these experiments cannot provide accurate predictions due to the complexity of debonding process. In this regard, this paper is aimed to investigate the debonding strength of FRP composites using novel models of Extreme Learning Machine (ELM) in co-operation with Teaching–Learning based Optimization (TLBO), Particle Swarm Optimization (PSO) and gray wolf optimizer (GWO). By comparing corresponding values of coefficient of determination (R2) and root mean square (RMSE) in three hybrid models, the best performance in predicting the debonding strength of FRP composites was obtained for ELM-GWO in comparison with ELM-PSO and ELM-TLBO. Considering the best RMSE value as 0, GWO with RMSE = 2.5057 showed the closest value to 0 compared to PSO (2.73) and TLBO (5.58). On the other hand, since the best value of R2 is closest to 1, GWO with R2 = 0.9504 indicated a better performance compared to PSO (0.9431) and TLBO (0.7554).

Experimental and numerical damage analysis of low-velocity drop weight impact of polyethylene self-reinforced composite laminates for transportation applications

This study covers a low-velocity impact property analysis of Polyethylene self-reinforced composites (PET-HDPE/HDPE SRC)through experimental and numerical methods emphasizing the influence of interfacial properties. Self-reinforcing a polymer material has gained a lot of attention due to maximum exploration of their light density characteristics with better chemical compatibility and interfacial adhesion of matrix and reinforcement, resulting in higher fuel efficiency. Reusability of self-reinforced thermoplastic composites even without separating their constituent materials has been observed to be aiding the circular economy strategies. The study aimed to analyze the peak load characteristics, energy-absorbing characteristics, and damage response of these materials processed through the hot compaction technique and subjected to a drop mass impact test. Fractographic visual inspection, optical macrographs, Scanning electron microscopy analysis, and through transmission ultrasonic C-scan were employed to study the damage evolution and failure mechanisms under the low-velocity impact. Three levels of impact energy were included in the test matrix, and initiation of the damage, nature of the matrix, interface debonding, matrix and fibre failures could be identified through the inspection of the damage cross-section at the impact eye. A finite element model developed through commercial FEA packages (Abaqus) was utilized for the complex mechanisms of damage and failure. Weak interfacial adhesion due to the self-lubricating nature of the polyethylene fibre surface contributed to the fibre pull out during the drop weight impact. A qualitative analysis and correlation of the nature of surface damage and internal damage were also studied, which are the factors that are necessary for the development of cargo containers and marine/aerospace ultralight luggage applications.

Acoustic emission-based monitoring of fatigue damage in CFRP-CFRP adhesively bonded joints

Adhesively bonded joints are being increasingly applied in modern structures. However, manufacturing defects and particularly harsh operative conditions may cause local debonding and catastrophic failures. Structural health monitoring (SHM) and non-destructive testing (NDT) procedures are then needed to evaluate the in-service structural integrity of adhesively bonded joints. In this research, an adhesively bonded single-lap joint, both adherends of which are manufactured using a carbon fibre-reinforced polymer (CFRP) composite, is subjected to constant amplitude fatigue loading. During such a test, the integrity and damage condition of the joint is continuously monitored using acoustic emission (AE), while the test itself is periodically interrupted in order to apply micro-computed tomography (μCT) to the specimen, with the aim of investigating the real features of the developing fatigue damage. The results show that, after suitable elaboration and filtering by means of pattern recognition algorithms, acoustic emission-based monitoring allows for effective identification and characterisation of the development of fatigue damage in adhesively bonded joints.

Multi-scale study on interfacial bond failure between normal concrete (NC) and ultra-high performance concrete (UHPC)

It is a promising way to strengthen and repair the damaged normal concrete (NC) structure with ultra-high performance concrete (UHPC), and the interfacial performance between NC and UHPC is a critical issue. This paper aims to reveal the debonding failure performance between UHPC (repair material) and NC (substrate material) under tensile loading and shear loading. A multi-scale analysis method is established to simulate the mechanical behavior of the NC-UHPC interface, considering the complex interface geometry on the meso-scale. The failure of NC matrix is described by the elastic-plastic damage model in form of coupled gradient-enhanced damage evolution, the interface is represented by the cohesive zone model (CZM), and the UHPC is characterized by the second-order mean-field homogenization (MFH) method. After extracting the roughness characteristic parameters of the tested interfaces, the representative volume element (RVE) corresponding to the roughness is established, the load transfer and the debonding failure behavior are investigated, and the effective traction-separation law (TSL) is obtained. Finally, the tensile and the shear separation mechanisms of the NC-UHPC interface are revealed, and the effects of the roughness and strength of the interface on the macro shear and tensile strength are evaluated. Both the interface roughness and the substrate concrete strength have positive effects on the mechanical properties of the interface.

A 2D generic multi-surface cohesive zone model for simulating FRP-to-concrete mixed-mode debonding failure

This paper proposes a 2D generic multi-surface cohesive zone model to simulate the debonding failure process of FRP-to-concrete joints within the framework of plasticity theory. The model combines a tension cut-off yield surface with a Coulomb friction yield surface, which can accurately predict the coupled mixed-mode debonding behaviour. Non-associated flow rule is adopted by the Coulomb friction yield formulation to reproduce the dilation effect, while the tension cut-off criterion is responsible for simulating the separation in the normal direction between two bonded substrates. Given the potential non-convergence problems caused by the presence of vertex region at the intersections between two yield surfaces, a remedy measure using the implicit backward Euler integration method incorporating Koiter’s rule and coupled independent state variables is applied. The proposed 2D interface model is versatile, and its accuracy has been validated by comparing the predicted results with their test counterparts from literature in different aspects, including the capacities of capturing mixed-mode failure, dilation behaviour, lateral compression effect, FRP deformation, and local bond stress-slip relationship. The model’s good compatibility with the constitutive relationship of CDP (concrete damaged plasticity) is also demonstrated.

Experimental study on seismic performance of prefabricated RC columns with non-contact lap splices

A column-column connection particularly suited to the innovative prefabricated RC columns with precast hollow shell, is proposed in this paper. The connection involves extra bars in the post-cast core forming non-contact lap splices with the longitudinal bars in the precast shell. Since neither extra instrument nor material is needed, the proposed connection allows for fast erection as well as easy quality control, avoiding the shortcomings of common precast column-column connections. The effectiveness of the proposed connection was investigated experimentally. Ten precast specimens and two cast-in-place specimens were tested under quasi-static cyclic loading. Test results including damage progression, load capacity, ductility, energy dissipation and strain distributions of the specimens are reported. Precast specimens with non-contact lap splices exhibited similar hysteretic responses to the cast-in-place reference specimens, validating the reliability of the connections. The precast columns can achieve almost the same load and deformation capacity as the cast-in-place columns by doubling the stirrup ratio in the splice region. No de-bonding failure was observed at any old-new concrete interface for all specimens. Based on the test results, design suggestions are given to achieve satisfying connection performance.

A simplified reinforcement and fracture mechanism analysis model of epoxy nanocomposites based on finite element simulation

Understanding the reinforcement and fracture mechanism of polymer matrix nanocomposites is crucial for the design of high-performance composite materials. By taking boron nitride@boronate polymer core-shell nanoparticles modified epoxy resin nanocomposites (EPNCs) as an example, a reinforcement and fracture mechanism analysis model of nanocomposites was established through the combination of experiments and simulations. Instead of the traditional programming method by using the external language, a new modeling method was introduced with the help of Digimat. The results indicated that the interface force between (within) EP matrix and nanoparticles, the shell thickness and nanoparticle content play important roles in the reinforcement and fracture of EPNCs. The bending strength increases with the raising of particle content, but decreases with the increasing of shell thickness. The simulated results were consistent with the experiments. The interface force evolves according to the order of interfaces within particles and their shell > matrix-shell > matrix interior. A proper interfacial force can make interfacial debonding and matrix failure occur at the same time, thus improving both the strength and toughness of nanocomposites. This model construction will provide theoretical guidance for nanocomposites design and the clarification of reinforcement mechanism. • Cross-examination of analytical, numerical and experimental results is conducted. • Appropriate interface, thin shell and particle content play important roles in composites reinforcement mechanism. • Finite element evaluation of core-shell nanoparticles reinforced epoxy resin composites wais established.