Delamination Propagation Research Articles

Experimental and numerical studies on low-velocity impact of laminated C/SiC structures

Laminated C/SiC(carbon fiber reinforced silicon carbide composites) has the complicated nature of composite failure which include cracks for void defects at the meso and micro scales, complex cracks propagation of tunnel cracks, matrix cracks, delaminations and fiber cracks, orthotropic, and pseudoplastic behavior. It has technical challenge to solve all of them for complicated-mechanics problems by using multi-scale methodology. This paper focused tackling it by a model that lies between macro and meso scales, and proposed a new conceptual 3D FE-PDM(Finite Element - Progressive Damage Method). 3D FE-PDM was validated by the experiments of low-velocity impact of 2D C/SiC and 3D needled C/SiC. Damage initiation and evolution were controlled by strain in order to preventing stress chaos which could occur as cracks leading local stress relief. The multi-linear constitutive relations were adopted in orthotropic directions. The coupled effects of stresses between in-plane and out-of-plane were computed by adding damage coefficients into stiffness matrix. Cohesive Zone Method was used for delamination. The PDM approach was introduced for the 3D elements for intralaminar and cohesive elements for the interfaces. A parametric inversion methodology was put forward to determine the model parameters iteratively by comparing simulation results with the load-time curves, damage CT details of the experiments. Validation implies that, with small number of parameters, 3D FE-PDM is able to predict damage initiation of each phase knee, damage evolution, and load–displacement curve with good convergence for the low-velocity impact case. 2D woven and 3D needled non-woven C/SiC both have impact energy threshold and different damage evolution types.

Fatigue delamination propagation: Various effects on results

AbstractIn this investigation, three subjects are considered. First, the effect of the human factor is examined. In carrying out analyses of fatigue delamination propagation tests on laminate composites, the delamination length must be measured. The human effect on measurement of the delamination length by different investigators is discussed. A limited influence of the human factor on the measurement of the delamination length , as well as on delamination propagation rate , is observed in this study. Secondly, the paper proceeds to discuss the influence of the ratio on the fatigue delamination growth rate. It is found that a higher rate of crack/delamination propagation is associated with lower ratios which appears to contradict conventional wisdom. This behavior is confirmed in tests. Thirdly, a comparison between the fatigue propagation rates of two material systems is considered. It is concluded that the energy release rate used to assess these materials should not be normalized.

Distributed strain monitoring of overburden delamination propagation at a deep longwall mine

Clear understanding of overburden failure propagation during underground mining is critical in managing safety and environmental issues such as rock burst hazards, groundwater inrush and longwall convergency. This paper presents an in-situ monitoring study of overburden strain dynamics at a kilometre-deep longwall mine using distributed fibre optic sensing technology (DFOS). A deep borehole was drilled from the ground surface to near the mining seam and installed with an optical fibre cable to detect rock deformation in a contiguous fashion. In addition, a Global Navigation Satellite System (GNSS) device was installed at the borehole collar to monitor surface subsidence. The results suggested that strata delamination contiguously extended to 347 m, about 34 times the mining thickness. The remaining 600 m thick strata above this height behaved as the intact zone. Such an overburden deformation pattern resulted in minor surface subsidence of only 0.6 m or 6% of the mining thickness. A step-wise, upward breakage of the optical fibre cable (due to excessive strain) was observed and found to correlate with other ground behaviours, including an increase in the total microseismic energy and periodic weighting on the longwall supports. These observations corroborate that the dynamic deformation of overburden is primarily governed by competent stratum units, i.e., the key strata. The monitoring results have served to develop a reliable mine-scale 3DEC model for predicting stress redistributions in the subsequent longwall panels for preventing dynamic hazards. The study also demonstrates that DFOS-based strain monitoring can be a valuable tool to investigate overburden responses to mining and has significant potential for applications in various mining methods, such as block caving, sub-level caving and open stopping.

Damage formation and evolution mechanisms in drilling CFRP with prefabricated delamination defects: Simulation and experimentation

Delamination is a common defect in carbon fiber reinforced polymer (CFRP) during the molding process. Accurately understanding the formation and evolution mechanisms of drilling damage in CFRP with delamination defects is helpful for effectively suppressing drilling defects with delamination. In this study, a macro-micro finite element model (FEM) of CFRP with prefabricated delamination defects during drilling is established to simulate and analyze the damage formation and evolution behavior. The circular polytetrafluoroethylene (PTFE) films are employed to simulate the delamination defects in CFRP. These samples with different sizes of prefabricated delamination defects are prepared for the drilling experiments. The results show that the maximum errors of the thrust force and the exit damage factor between the simulation and experiments are 8.75% and 4.2% respectively, indicating good reliability of the simulation model. Under the condition of CFRP with delamination defects, as the size of the delamination defects increases, the maximum thrust force decreases, while the maximum delamination propagation length and exit damage increase. Compared to the case without delamination defects, when the delamination diameter is 7 mm, the delamination propagation percentage and the maximum stress in CFRP increase by 52.17% and 155.4% respectively, and the maximum increment of the exit delamination damage factor is 38%.

Delamination analysis of high-temperature superconducting tapes based on a random defect model

Random microscopic defects have been found in the fabrication of rare-earth-barium-copper-oxide (REBCO) high-temperature superconducting (HTS) tapes. Interlaminar failure of the tape is more likely when the interfacial bonding strength is reduced as a result of defects, which seriously jeopardizes the dependability of large magnet systems. In this paper, a three-dimensional finite element model (FEM) of the tape with random defects is developed using the Weibull distribution function to evaluate the effect of defects on the delamination of the tape. The delamination behavior under two loading scenarios were conducted (Case-I: out-of-plane tensile and Case-II: axial compression). The result show that the interfacial bonding strength is significantly affected by the defect fraction. The random characteristics of defects and their impact levels can be traced through different parameters. For case-I, the theoretical results of the effective interfacial bonding strength are in good agreement with the numerical results. During the delamination process, the occurrence of defects leads to stress oscillations in the constituent layers. Under axial compression loading (Case-II), the defect dramatically reduces the critical capacity of the tape. With increasing defect fraction, the rate of delamination propagation grows noticeably.

Thermal cycling effects on the mode-I delamination of multilayer laminated composites: An experimental-numerical approach

In this research, the influence of thermal cycling on the fracture toughness and maximum load in the mode-I delamination of polymer matrix composites (PMCs) was investigated. To reduce the effect of the remote ply orientation on the fracture toughness during initiation and propagation delamination, double cantilever beam (DCB) specimens with a stacking sequence of unidirectional [0]16 were considered. The specimens were subjected to thermal-cycled loading between 15°C and 65°C for 50-150 number cycles. One group of un-cycled specimens was examined at the commencement of the research as a control group to determine the effects of thermal cycling loading on mechanical characteristics of the second group specimens. During the DCB experiment, the specimens were inspected by 2 real-time cameras to record the delamination length and initial crack tip opening displacement (ICTOD). The strain energy release rate (SERR) approach was used for obtaining the critical fracture toughness from the experimental data. By employing the digital image correlation (DIC) method, the initial crack tip separation profile was obtained. The measured bridging laws with the cohesive zone elements model are used to accurately simulate the delamination propagation in DCB specimens. Investigation of load variations revealed that critical fracture toughness in the mode-I of delamination is firmly affected by the thermal cycling process.

Predicting Interfacial Failure in Laminate Composite by using the Finite Element Method (FEM) : A Cohesive Zone Modeling Approach for Delamination

This study explores the interfacial failure modes of laminate composite, focusing ondelamination and debonding. To simulate these failures, a cohesive zone model (CZM) is employed, witha key component being the traction-separation law that characterizes softening near the delamination tip.The study demonstrates the modeling of debonding using the COMSOL® 5.6 software based on theFinite Element Method (FEM) decohesion model. The CZM's effectiveness in predicting mixed-modesoftening and delamination propagation is showcased through a model of mixed-mode bending in acomposite beam. By subjecting the beam to various loading conditions, the CZM accurately predictssoftening behavior and delamination progression. This research highlights the CZM's value inunderstanding and predicting interfacial failure, enabling improved design and structural integrity oflaminate structures.

Experimental and numerical analysis of residual compression strength after Low-Velocity Impact of carbon/epoxy composite plate

A composite laminate is susceptible to Low-Velocity Impact (LVI) load, leading to Barely Visible Impact Damage (BVID) accompanied by invisible damage in the form of delamination. Such delamination is significantly reduced the compression strength of the composite laminate plate. The present work provides an experimental and numerical analysis, based on finite elements, on residual compression strength after the low-velocity impact of carbon/epoxy composite plate. Five specimens of 16 layers Unidirectional carbon/epoxy composite plate with fiber orientation [+450/900/-450/00/+450/900/-450/00]s have been tested subject to low-velocity impact load, with a single use of impact energy value of 2.75 Joule/mm, followed by compression test. Moreover, another similar five specimens tested compression before impact to measure its compression strength. Experimental results were observed to identify the profile and size of total-projection delamination after impact and after compression and compression-strength before and after impact. The Finite Element analysis is based on the utilization of cohesive zone elements with Benzeggagh-Kenane fracture criterion to predict the initiation and propagation of delamination, Kirchhoff based formulation of continuing shell element to model stiffness of the laminate, and Hashim-Rotem damage mechanism to predict intralaminar damages.

Fatigue delaminations in composites for wind turbine blades with artificial wrinkle defects

Out-of-plane wrinkles are manufacturing defects that affect the structural performance of wind turbine blades under fatigue. Glass Fiber Reinforced Polymer (GFRP) laminated specimens embedded with artificial wrinkle defects at two severity ratios (amplitude/half-wavelength) show different resistance to cyclic loading when tested under tension–compression fatigue. This work presents the validation of a fatigue formulation for the prediction of fatigue damage from wrinkles characteristic of wind turbine blades. The validation is performed through numerical models combined with experimental tests in which the fracture framework aims at predicting crack initiation and delamination propagation. The experimental fatigue program loaded the specimens with R=−1 to assess damage growth. The fatigue damage mechanism is quantified as a stiffness degradation, and the damage level is classified into five phases. Comparing the two severity types of wrinkles, the fatigue lifetime for equal external loading differs by approximately two decades. This difference is also captured by the numerical predictions. The lower the aspect ratio (AR), the higher the defect resistance to reversed fatigue loading. The numerical models captured the qualitative behavior of the SN curves and delamination fracture path and location observed in the experiments.

Mode I delamination R-curve in poplar laminated veneer lumber

Recent studies have shown that plywood, laminated veneer lumber are very efficient crashworthiness materials. Therefore, there is a need to determine the fracture toughness of these wood composite materials to be able to model their static, dynamic damage behavior. This study reports the results of the delamination propagation of plywood under mode I loading. Two different double cantilever beam specimens made of poplar were compared: one with an interfacial fiber orientation of 0°/0°, the second with 0°/90°. Failure scenarios, patterns are analyzed to establish a comparison between the two configurations, compute consistent R-curves.

Evaluations on VCCT and CZM methods of delamination propagation simulation for composite specimens

Evaluations on VCCT and CZM methods of delamination propagation simulation for composite specimens

Effect of graphene reinforcement distribution on energy release rate and vibration of thermally pre/post-buckled delaminated composite plates

The nonlinear thermal stability responses of functionally graded graphene-reinforced composite (FG-GRC) laminated plates with single or multiple through-the-width delaminations, are investigated in the article. The possibility of delamination growth is evaluated using the three-dimensional crack tip element (3D-CTE) method, which determines the energy release rate (ERR) at the delamination edge. Furthermore, the influence of delamination configurations and the types of graphene reinforcement distribution patterns, on the free vibration of FG-GRC delaminated plates in thermally pre/post-buckled regimes is evaluated. The von Karman geometrical nonlinearity is adopted in a solution based on the layerwise third-order shear deformation theory (TSDT). The nonlinear equilibrium equations derived by the minimum total potential energy principle are solved using the Ritz method in conjunction with the Newton–Raphson iterative procedure. A three-dimensional finite element model is also developed using ABAQUS to corroborate the accuracy of the theoretical results. Parametric studies reveal that while the FGX graphene distribution pattern improves the bending stiffness of delaminated composite plates more than FGA, the ERR at the near surface delamination edge in FGX pattern is twice as high as that in FGA. This implies that the possibility of delamination propagation in FGX plates can be higher than FGA. Additionally, while the fundamental frequency of the FGX plate with and without delamination exceeds the frequency of other graphene distribution patterns at the reference temperature, its natural frequency is the lowest among all patterns in the post-buckled regime.

A semi-analytical model for failure analysis of delaminated composites under fatigue loading

Relative to static conditions, fatigue damage prediction of delaminated composites is widely recognized as a much more challenging problem, due to the gradually considerable reduction of mechanical characteristics and the delamination propagation, which further leads to catastrophic failure of laminates. To completely evaluate failure behaviors of delaminated composites under fatigue loadings, a semi-analytical model was established based on the residual stiffness theory and brittle damage mechanics. A stiffness degradation model was presented to describe the reduction of stiffness properties of composites, a residual strength model was found to predict the delamination propagation and strength degradation during cyclic loadings, and a failure evaluation criterion was proposed to judge the ultimate fatigue failure of laminates. Stiffness degradation tests and compressive fatigue tests were designed and conducted. Predicted results were highly consistent with experimental outcomes, which validated the effectiveness and accuracy of the semi-analytical model for the evaluation of fatigue failure behaviors of delaminated composites. Based on the proposed model, the strength degradation processes of delaminated composites in this work can be determined, and a safety load region can be additionally presented, which can provide significant guidance for the safety design of delaminated composites under fatigue loadings.

Unraveling the failure mechanism of wire arc additive manufactured low carbon steel under tensile and high cycle fatigue loading

Wire arc additive manufacturing (WAAM) is one of the common additive manufacturing processes for efficiently building large components due to its high deposition rate and higher catchment efficiency with an easy and relatively simpler arrangement. However, WAAM components often observe defects that adversely affect some mechanical properties. The present work employs a two-camera digital image correlation (DIC)-based technique for simultaneous strain measurements on two mutually orthogonal surfaces to capture the strain accumulation due to defects and subsequent failure behavior under uniaxial tensile loading of WAAM deposited ER70S-6 low carbon steel samples. The elastic cyclic loading tests are also performed at different stress amplitudes, and their fracture surfaces are analyzed with scanning electron microscopy. Due to the weak interlayer consolidation, multiple delaminations and strain accumulation sites are observed. Propagation of delamination contributed towards the failure, and dimples as well as intergranular fractures are observed on failure surfaces. Premature failure with a reduced number of cycles to failure is observed during high cycle fatigue tests due to catastrophic fast failure in the neighborhood of the internal defects. While the fatigue crack initiation and propagation are distinctly observed on fracture surfaces, transition regions from fatigue fracture and fast fracture are mostly obscure.

Delamination Behavior of Highly Stretchable Soft Islands Multi-Layer Materials

Stretchable electronics rely on sophisticated structural designs to allow brittle metallic conductors to adapt to curved or moving substrates. Patterns of soft islands and stable cracks in layered silver-PDMS composites provide exceptional stretchability by means of strain localization as the cracks open and the islands strain. To investigate the reliability and potential failure modes, we study the initiation and propagation of delamination in dependence of structure geometry and quality of the metal-polymer bonding. Our numerical experiments show a well-bonded metal film to be under no risk of delamination. Even weakly bonded metal films sustain moderate strains well above the limits of classical electronic materials before the onset of delamination in the soft islands structures. If delamination occurs, it does so in predictable patterns that retain functionality over a remarkable strain range in the double-digit percent range before failure, thus, providing safety margins in applications.

A novel method to include crack-induced delamination in a fatigue damage predictive procedure for composite laminates

A novel procedure is proposed to include crack-induced delamination in a damage-predictive framework based on discrete damage modelling. Delamination initiation and propagation are treated separately based on experimental damage observations. Compared to alternative methods, the use of numeric analyses is strongly reduced, thus significantly increasing the efficiency of the predictive procedure. The proposed method is validated against fatigue data from the literature and from new experimental tests, showing a satisfactory agreement.

The role of intralaminar damages on the delamination evolution in laminated composite structures

Delamination is a major failure mode affecting laminated composite structures. This failure mechanism, if not properly monitored, can lead to uncontrolled cracks growth and premature structural collapse. Thus, predicting delamination propagation is mandatory to determine the structural integrity. At present, delamination has been extensively investigated in laminated composite structures but only a few studies have been performed on how the intralaminar damages influence the interfacial release energy and, consequently, the delamination evolution. In this paper, the well-established SMart-Time XB delamination simulation tool, has been coupled with a Hashin Criteria based User-Material Subroutine (UserMat) to study the role of the intralaminar damages in delamination propagation. A benchmark case based on the mixed-mode I/II Single Leg Bending (SLB) specimen for delamination evolution assessment under quasi-static loading has been investigated. Subsequently, a composite material plate, characterized by an artificial circular delamination, under compression has been considered. This study proved to be valuable by underlining the influence of fibre and matrix breakage on the interlaminar damages evolution. Interestingly, taking into account the effect of intralaminar flaws changes the local energy release rates values on the delamination front and, consequently, the crack shape and evolution.

An efficient ERR-Cohesive method for the modelling of delamination propagation with large elements

An efficient ERR-Cohesive method for the modelling of delamination propagation with large elements

Delamination Effect on the Buckling Behaviour of Carbon–Epoxy Composite Typical Aeronautical Panels

The instability of structures due to compression is one of the most critical issues related to aircraft components. Especially in composite materials, which have poor out-of-plane mechanical properties, the buckling load must be assessed to ensure that the structures are within the safe limits compared to the operating loads. In the presence of delamination, the compression instability of structures becomes catastrophic, as the propagation of delamination can dramatically reduce the stiffness of the structure almost instantaneously. During the operational life of composite aircraft components, one of the most common events that can occur is low-velocity impact with foreign objects, which is one of the primary reasons for delamination. In this paper, a sensitivity analysis is presented on a typical aerospace reinforced panel with a circular delamination, representative of an impact damage. Different configurations have been analysed, varying the radius and position along the thickness of the delamination. Furthermore, some geometric parameters of the panel have been modified to evaluate how the buckling load and the propagation of interlaminar damage evolve.

A Critical Review on Nanoparticle Filled Adhesives for Structural Applications

The objective of this review paper is to highlight some of the noteworthy research that has been done on the use of nanoparticles (NPs) to improve the performance of adhesively bonded joints (ABJs) against delamination initiation and propagation. Various nanoparticle applications, such as carbon-based, ceramic-based, and mineral-based nanoparticles, are covered. Interlaminar shear strength, fracture toughness, and fracture energy are the major parameters that have been considered for enhancing FRP delamination and fatigue resistance.The reported results indicatethat the inclusion of NPs in polymeric matrices leads to improvement of various material properties,even though some discrepancies in the results have been noted. Notwithstanding, additional researchis required to address some of the issues that have not yet been tackled.