Fiber Compressive Failure Research Articles

Mechanical properties and failure analysis of ring-stiffened composite hulls under hydrostatic pressure

Ring stiffeners improve the buckling resistance of thin-walled hulls. In this study, theoretical models of buckling and strength failure of ring-stiffened composite hulls (RSCHs) were used to determine the design parameters. The hulls were prepared by filament winding on a mould composed of multi-petal-combined foams and steel shafts. The experimental results showed that the hydrostatic bearing performance of RSCHs was 1.79 times that of an unstiffened composite hull (USCH) with the same weight-to-displacement ratio (WDR). The crack in the damaged stiffened hulls penetrated the entire axis and expanded circumferentially, resulting in a stiffener fracture. Imperfections related to thickness deviations were introduced into a nonlinear buckling model by considering progressive damage. In contrast to the failure mechanism of USCH, the failure pressure of RSCHs was not at the peak of nonlinear buckling, and fibre compressive failure at 90° on the outermost layer of the skin was dominant. The error between simulated and experimental results was 4.64 %. The parameter analysis indicated that the stiffener height and width had different effects on the buckling load. However, when only the same type of strength failure occurred, both were independent of the load. This study demonstrated the load-bearing advantages of RSCHs for ocean engineering applications.

Experimental and finite element modelling analysis on the embedment performance and failure mechanisms of flattened-bamboo composite with the effect of fiber orientation angle

This paper focused on a newly engineering use flattened-bamboo composite (FBC) and studied the effect of fiber orientation angle (0° - 90°, 15° intervals) on FBC’s embedment performance and failure modes by half hole test. The results indicated that with larger fiber orientation angle, both the embedment strength and initial stiffness gradually decreased (embedment strength: 52 ∼ 26 MPa, initial stiffness: 27062 ∼ 11149 kN/mm), and Hankinson’s formula could effectively predict FBC’s embedment strength with error less than ±7 %. Combing the experimental phenomenon and scanning electron microscope (SEM) results, the failure modes of embedment specimens were classified. For angles of 0° and 15°, the failure mode was a mix of fiber crushing failure and split failure between fibers. For angles from 30° to 60°, the phenomenon of fiber being crushed became less obvious, only small cracks were witnessed around the half-hole area. For angles of 75° and 90°, the bamboo fiber compression failure perpendicular to fiber direction dominated, and two horizonal cracks happened on both sides of the specimen. A damaged constitutive model using continuum damage mechanics was proposed for simulating FBC’s embedding failure modes, and the proposed model was verified by comparing with the experimental phenomenon.

Damage and failure mechanisms of carbon fiber reinforced composite thin-walled bushings under hygrothermal-mechanical loadings

Numerous thin-walled bushings, injection-molded from AS4 short carbon fiber reinforced polyetherketone (AS4/PEK) composites, are employed in the chains of stenter heat-setting machines. These bushings rapidly deteriorate under the hygrothermal-mechanical loadings prevalent in their service conditions. This necessitates regular replacements, critically limiting machine efficiency. In this paper, considering hygrothermal-mechanical loadings, the macro–micro dual-scale damage model of composite bushings is established. The wet and thermal effects are introduced into constitutive models and damage criteria based on the macro–micro mechanics of composites and their constituents. The micro-damage and macro-destruction phenomena in the bushing are analyzed, and the related measures are proposed to delay its failure. Comparing the simulation results with the test, the macro–micro damage and failure behavior are discussed for the failed bushing. It reveals that stress concentrations near AS4 fibers initiate interfacial damage and microcracks in the PEK matrix, inciting interface debonding and matrix fragmentation, ultimately provoking composites failure. Increasing the interface thickness can delay the onset of damage. Fiber tension failure, matrix tensile, and compressive failure induce destruction at the component extremities. According to the influence of hygrothermal performance, within the glass transition temperature range of 160 °C to 240 °C, selecting composites with higher glass transition temperatures can enhance the failure strength of bushings by 19 %. Conversely, within a moisture absorption range of 0.5 % to 0.8 %, opting for materials with lower moisture absorption decreases the failure strength of bushings by 37 %. Optimal failure strength is achieved with composites having a 0.5 % moisture absorption rate and a 240 °C glass transition temperature.

A Numerical Method for Unstable Propagation of Damage in Fiber-Reinforced Plastics with an Implicit Static FE Solver

Finite element analyses of the propagation of damage such as fiber compressive failure and delamination have greatly contributed to the understanding of failure mechanisms of fiber-reinforced plastics owing to extensive studies on methodologies using Continuum Damage Mechanics and Fracture Mechanics. Problems without the need for consideration of inertia, such as Double-Cantilever Beam tests, are usually solved by implicit FE solvers, and explicit FE solvers are appropriate for phenomena that progress with very high velocity such as impact problems. However, quasi-static problems with unstable damage propagation observed in experiments such as Open-Hole Compression tests are still not easy to solve for both types of solvers. We propose a method to enable the static FE solver to solve problems with unstable propagation of damage. In the present method, an additional process of convergence checks on the averaged energy release rate of damaged elements is incorporated in a conventional Newton–Raphson scheme. The feasibility of the present method was validated by two numerical examples consisting of analyses of Open-Hole Compression tests and Double-Cantilever Beam tests. The results of the analyses of OHC tests showed that the present method was applicable to problems with unstable damage propagation. In addition, the results from the analyses of DCB tests with the present method indicated that mesh density and loading history are not significantly influential to the solution.

Microscale and mesoscale modeling for compressive failure in unidirectional carbon fiber reinforced polymer composites with random distribution of fiber misalignments

AbstractCompressive strength and failure mode of carbon fiber reinforced polymer (CFRP) composites are affected by the severity of fiber misalignment. In this paper, numerical models based on computational micromechanics are proposed to investigate the correlation between fiber misalignment and compression failure. A single‐fiber micromodel including fiber, matrix, and interface phases is first developed to capture the influence of misalignment severity on the material failure mode. The failure longitudinal stress distribution in the fiber predicted by the micromodel indicates that the failure mode depending on the initial misalignment can be identified as uniform compression failure, compression‐bending combination collapse, and fiber buckle. A mesoscale 2D model with multiple fibers is then constructed to investigate the kink band formation. This model takes into account the distribution of fiber misalignments to capture the key geometric features of fiber misalignment that influent the compression failure in realistic composite materials at the structural scale. The results show that fiber misalignment angle amplitude, misalignment dispersion (characterized by the standard deviation), and misalignment wavelength are the key parameters of fiber misalignment, which have significant effects on compression strength and kink band geometry.Highlights Single‐fiber model to capture the effect of misalignment severity on failure mode. Multi‐fiber model with randomly distributed fiber misalignments. Failure mode depending on the severity of initial misalignment was identified. Key parameters of misalignment on compression strength and kink band geometry.

Characterization of Failure Behavior in Unidirectional Fiber-Reinforced Polymer via Off-Axis Compression on Small Block Specimens.

An experimental investigation was focused on the failure behavior of unidirectional fiber-reinforced polymers when subjected to combined longitudinal/transverse compression and in-plane shear due to off-axis loading. Block-shaped and end-loaded specimens, spanning ten different fiber orientations (0°, 5°, 10°, 15°, 20°, 30°, 45°, 60°, 75°, and 90° with respect to the loading direction), were loaded to ultimate failure using a dedicated fixture. Different failure modes, including longitudinal compression, in-plane shear, and transverse compression, were identified, along with distinctive characteristics of the corresponding failure envelopes. Four physically based failure theories-Hashin, Camanho, Puck, and LaRC05-were subjected to a comparative analysis. Criteria derived from the concept of the action plane consistently outperformed in describing matrix-dominated failures, providing both qualitative and quantitative predictions of failure stresses and fracture plane orientation. However, for fiber-dominated failures, these theories seem to fall short in providing satisfactory predictions, particularly in accurately describing the influence of shear on fiber compression failure. Although criteria based on fiber-kinking theory can reasonably explain the formation of kink bands, they tend to yield overly conservative results. Recalibrations and minor refinement based on experimental results were implemented, leading to an improved agreement. Finally, the constructive role of off-axis compression tests in characterizing the failure behavior of unidirectional composites is discussed.

Study on the O-/ U-type collapse of reinforced thermoplastic pipes (RTPs) subjected to hydrostatic external pressure: Experimental tests and numerical analysis

Due to the anisotropy and progressive failure of composites, the collapse problem of RTPs is more complex compared with that of traditional steel pipes. To address this problem, the collapse behavior of RTPs subjected to external pressure was studied by conducting collapse tests and numerical simulations. Two different collapse modes including the O-type and U-type mode were observed during the collapse tests. It was the first time to observe the U-type collapse mode of RTPs in open literature. For O-type collapse mode, the cross-section turned into an ellipse. And for U-type collapse mode, it turned heart-shaped. Meanwhile, numerical simulations were conducted by combing eigenvalue analysis and arc-length method, in which the progressive failure of composites was considered by employing a fracture energy degradation model based on the Hashin criterion. To simulate the U-type collapse mode, eccentricity was also introduced. Research results indicated that the critical pressure obtained by tests and numerical simulations agreed well for both O-/U-type collapse modes. The collapse process could be described as “contraction-collapse point-large deformation”. It was found that the progressive failure of composites would reduce the pressure-resisting capacity greatly. For the composites, the shear failure, the matrix and fiber compressive failure were dominant failure modes.

Modeling Progressive Damage and Failure of Single-Lap Thin-Ply-Laminated Composite-Bolted Joint Using LaRC Failure Criterion.

Thin-ply composite failure modes also significantly differ from conventional ply composite failure modes, with the final failure mechanism switching from irregular progressive failure to direct fracture characterized by a uniform fracture with the reduction of the ply thickness. When open holes and bolt joints are involved, thin-ply-laminated composites exhibit more complex stress states, damage evolution, and failure modes. Compared to the experimental study of thin-ply-laminated composite-bolted joints, there are few reports about numerical analysis. In order to understand the damage evolution and failure mechanism of thin-ply-laminated composites jointed by single-lap bolt, a progressive damage model based on three-dimensional (3D) LaRC failure criterion combined with cohesive element is constructed. Through an energy-based damage evolution method, this model can capture some significant mechanical characteristics in thin-ply-laminated structures, such as the in situ effect, delamination inhibition, and fiber compressive kinking failure. The comparisons between the numerical predictions and experimental observations are made to verify the accuracy of the proposed model. It is found that the predicted stress-displacement curves, failure modes, damage morphologies, etc., are consistent with the experimental results, indicating that the presented progressive damage analysis method displays excellent accuracy. The predicted stress at the onset of delamination is 50% higher than that of the conventional thick materials, which is also consistent with experimental results. Moreover, the numerical model provides evidence that the microstructure of thin-ply-laminated composite performs better in uniformity, which is more conducive to inhibiting the intra-layer damage and the expansion of delamination damage between layers. This study on the damage inhibition mechanism of thin-ply provides a potential analytical tool for evaluating damage tolerance and bearing capabilities in thin-ply-laminated composite-bolted joints.

Parameter optimization of L-joint of composite sandwich structure based on BP-GA algorithm

Composite superstructure could provide excellent performances during surface combat. L-joint in the superstructure plays a significant role in the long-term service and would bear a complicated external load. In this paper, an all-composite L-joint was proposed and subjected to a bending test. A progressive damaged finite element analysis was performed to reveal its failure mode. An optimization based on the BP-GA algorithm was conducted to obtain the optimal geometries. The results showed that the primary failure mode of the L-joint was the crack of the stiffener outer skin. It was dominated by the fiber compressive failure. The average ultimate loadbearing capacity of the L-joint was 2.321 kN. And the simulated result was 10.09% lower than the experiment. The maximum relative error between the BP-GA prediction and actual values was less than 8%. The optimal structure obtained showed an enhancement of the load-bearing capacity about 1.41 times and stiffness about 1.65 times.

Dynamic response of the S-shaped composite foldcore sandwich structure under high-velocity impact loads

The dynamic response of the S-shaped foldcore sandwich structure was investigated at high-velocity impact load by combining the experimental and numerical methods. The ballistic tests were performed with a blunt projectile at different velocities, ranging from 49.7 m/s to 154 m/s, and the ballistic limit velocity (BLV) was estimated. The test results show that the impact location exerted great influence on the failure modes and energy absorption of the core. The BLVs of the sandwich structure are 64.2 m/s and 56.2 m/s for node and base impacts, respectively. And the different modes are observed for the top face sheet, the core and the bottom face sheet. The corresponding numerical simulations were performed by using Abaqus finite element software. The simulation results show that the BLVs predicted by the simulation correlated well with the tests. The failure modes of the sandwich structures with fiber fracture, delamination and compression failure are predicted reasonably. For the node impact conditions, the absorbed energy of the core is significantly higher than that of the top and bottom face sheet. For the base impact conditions, there is no significant difference on the energy consumed for three components of the structures.

An experimental and finite element investigation of compression-after-impact (CAI) behaviour of biaxial carbon fibre non-crimp-fabric (NCF) based composites

The damage mechanisms of biaxial non-crimp-fabric (NCF) reinforced composites with a quasi-isotropic [(45/-45)(90/0)]4s layup subject to low-velocity impact (LVI) and compression-after-impact (CAI) loadings are investigated. Experimental results indicate that fibre compressive failure in the 0° plies controls the peak load during CAI, which is influenced by the out-of-plane transverse deformation of the impacted specimen. The study proposes a novel finite element (FE) model to predict the CAI strength of the NCF specimen. While the number of delaminations in the LVI model is less than the actual number of the multiple delaminations in the test specimen, the same out-of-plane transverse deformation measured by the experiment is still captured. The strength predicted from the subsequent CAI model is in good agreement with the experiment. The study provides a potential numerical design tool for the use of NCF materials in damage-tolerant structures.

Study of SiC fiber axial compressive behavior using tensile recoil measurement

AbstractSiC fibers have been widely investigated as reinforcements for advanced ceramic matrix composites owing to their excellent high‐temperature properties. However, the axial compressive strength of SiC fibers has not been thoroughly studied. In this study, the compressive behavior of two SiC fiber types containing different compositions and thermal degradation were characterized by tensile recoil measurements. Results illustrated that the SiC fiber compressive strength was 30%–50% of its tensile strength, after heat treatment at 1200℃–1800℃ for 0.5 h in argon. The fiber compressive failure mechanism was studied, and a “shear‐bending‐cleavage” model was proposed for the recoil compression fracture of pristine SiC fibers. The average compressive and tensile strengths of the pristine SiC‐II fiber were 1.37 and 3.08 GPa, respectively. After treatment at 1800℃ for 0.5 h in argon, the SiC‐II fiber compressive strength decreased to 0.42 GPa, whereas the tensile strength reduced to 1.47 GPa. The mechanical properties of the fibers degraded after high‐temperature treatment. This could be attributed to SiC grain coarsening and SiCxOy phase decomposition.

Finite element analysis of drilling unidirectional CFRP in different ply orientation

In the new era of Industrial Revolution 4.0 (IR 4.0), the manufacturing processes are facing a new level of flexible mass production technologies. Hence, the high demands for simulations data of manufacturing production and operation are required for developing a Cyber-Physical Systems of smart machines. Some composite machining processes could be very expansive. Simulation is needed to reduce the manufacturing time and cost. Without considering the suitable parameter of drilling, damage occurs at the region over the hole’s boundary after the drilling operation is done. Thus, the goal of this research is to investigate the effects of drilling cutting parameter such as thrust force, drilling-induced damage and stress distribution of reinforcing carbon composite polymer (CFRP) laminate by developing a user-defined material model (VUMAT) subroutine in ABAQUS/EXPLICIT (ABAQUS, Dassault Systèmes®) for different fibre ply orientations. The failure mode such as fibre tensile failure, fibre compressive failure, matrix cracking and matrix crushing was modelled and analysed based on Hashin and Puck’s criterion. The stages of drilling operation were observed and described in this paper with the drilling cutting parameter and the damage of composite was finely defined. The results proved that the relationship of thrust force is directly proportional to the feed rate with the difference of computational model are 8 % higher than the experiment. Among the ply orientation sequence applied in the simulation, the result shows that [ / / ] and [ / / ] ply having higher thrust force with 401.84 N.mm and 390.53 N.mm at 500 mm/min feed rate as delamination extent, as the frequency of fiber pulls out at the exit region of the drilled hole increases as compared to the restricted fiber ply orientation 0˚ and 90˚.

An improved longitudinal failure criterion for UD composites based on kinking model

A longitudinal failure criterion for UD composites based on a kinking model was re-constructed guided by the principles of analytic geometry. The proposed method for determining the fiber initial misalignment angle considers the shear nonlinear response of the matrix. An expression accounting for the fiber matrix coupling failure was used to simulate shear-driven fiber compression failure. Different effects of the matrix shear on the fiber tensile and compressive failure was considered. Compared with the kinking model, the proposed criterion better predicted the compression failure mode, gave better agreement with the experimental results, and exhibited better adaptability for different fiber failure modes.

Experimental and numerical study of GFRP-reinforced circular steel tube under axial compression

The performance of glass fiber-reinforced epoxy resin (GFRP) reinforced circular steel tubes under axial compression was studied using both numerical and experimental methods. Through axial compression tests, the effects of steel tube thickness, GFRP winding angle (the angle between the axis of the tube and the tangential direction of winding fiber) and specimen length on specimens' failure modes and stability carrying capacity were studied; and proved that GFRP can improve the axial compression behavior of steel tube. A UMAT subroutine for GFRP that could consider 6 initial failure modes (fiber tension or compression failure, resin tension or compression failure and stretch or compression in-layer delamination failure) and damage evolution was developed, and then the axial compression processes of specimens were simulated; moreover, a further parametric analysis to examine specimens of different GFRP thickness and winding angle, steel tube diameter and thickness, as well as specimen length was carried out. A predictive formula was introduced to estimate the buckling load of specimen by modifying the Perry-Robertson equation. Finally, based on the simulation and the equivalent concept, the application of GFRP reinforced circular steel tube in the reticulated mega-structure was discussed.

Multi-Scale Progressive Damage Model for Analyzing the Failure Mechanisms of 2D Triaxially Braided Composite under Uniaxial Compression Loads

Based on continuum damage mechanics (CDM), a multi-scale progressive damage model (PDM) is developed to analyze the uniaxial compression failure mechanisms of 2D triaxially braided composite (2DTBC). The multi-scale PDM starts from the micro-scale analysis which obtains the stiffness and strength properties of fiber tows by a representative unit cell (RUC) model. Meso-scale progressive damage analysis is conducted subsequently to predict the compression failure behaviors of the composite using the results of micro-scale analysis as inputs. To research the free-edge effect on the local failure mechanisms, meso-scale models of different widths are also established. The stress-strain curves obtained by numerical analysis are verified with the experimental data. Results show that fiber and matrix compression failure inside the fiber tows are the major failure modes of the composite under axial compression. For transverse compression, the dominated failure modes are recorded for matrix compression failure inside the fiber tows. It is also presented that the free-edge effect plays an important role in the transverse mechanical response of the composite, and the failure behaviors of the internal fiber tows are strongly influenced as well.

Intralaminar fracture toughness of UD glass fiber composite under high rate fiber tension and fiber compression loading

Automotive and aeronautical composite structures can be subjected to dynamic loading scenarios (e.g. crash, bird strike). In both industrial areas, energy-based damage models for composite materials, able to predict initiation and evolution of damage of a composite ply under various loading conditions, are increasingly used. These models require the specification of fracture toughness parameters for the main failure modes. In previous works [1],[2], the authors have successfully enhanced a methodology suggested by Catalanotti et al. [3],[4] to measure the fiber failure crack resistance curves of a UD carbon fiber composite under dynamic loading. This methodology uses the relation between the energy release rate, the crack resistance curve and the size-effect law. For the determination of the size-effect law, double-edge-notched specimens of different sizes are tested. In this work, the developed approach is used for the measurement of the fracture toughness for fiber tension and compression failure of a UD glass-epoxy composite under high rate loading. Static tests are performed on an electromechanical test machine. For the high rate tests, split-Hopkinson bars for tensile (SHTB) and compressive (SHPB) loading are used. The results show, that the fracture toughness of the UD glass-epoxy composite, associated with the fiber failure modes, increases with increasing loading rate for tension as well as for compression. The observed strain rate effect on the fracture toughness of the glass-epoxy composite is more pronounced than for the carbon-epoxy composite investigated in [1],[2], in particular for fiber tensile failure.

Fracture toughness and crack resistance curves for fiber compressive failure mode in polymer composites under high rate loading

This work presents an experimental method to measure the compressive crack resistance curve of fiber-reinforced polymer composites when subjected to dynamic loading. The data reduction couples the concepts of energy release rate, size effect law and R-curve. Double-edge notched specimens of four different sizes are used. Both split-Hopkinson pressure bar and quasi-static reference tests are performed. The full crack resistance curves at both investigated strain rate regimes are obtained on the basis of quasi-static fracture analysis theory. The results show that the steady state fracture toughness of the fiber compressive failure mode of the unidirectional carbon-epoxy composite material IM7-8552 is 165.6kJ/m2 and 101.6kJ/m2 under dynamic and quasi-static loading, respectively. Therefore the intralaminar fracture toughness in compression is found to increase with increasing strain rate.

Compression Fracture of CFRP Laminates Containing Stress Intensifications.

For brittle fracture behaviour of carbon fibre reinforced plastics (CFRP) under compression, several approaches exist, which describe different mechanisms during failure, especially at stress intensifications. The failure process is not only initiated by the buckling fibres, but a shear driven fibre compressive failure beneficiaries or initiates the formation of fibres into a kink-band. Starting from this kink-band further damage can be detected, which leads to the final failure. The subject of this work is an experimental investigation on the influence of ply thickness and stacking sequence in quasi-isotropic CFRP laminates containing stress intensifications under compression loading. Different effects that influence the compression failure and the role the stacking sequence has on damage development and the resulting compressive strength are identified and discussed. The influence of stress intensifications is investigated in detail at a hole in open hole compression (OHC) tests. A proposed interrupted test approach allows identifying the mechanisms of damage initiation and propagation from the free edge of the hole by causing a distinct damage state and examine it at a precise instant of time during fracture process. Compression after impact (CAI) tests are executed in order to compare the OHC results to a different type of stress intensifications. Unnotched compression tests are carried out for comparison as a reference. With this approach, a more detailed description of the failure mechanisms during the sudden compression failure of CFRP is achieved. By microscopic examination of single plies from various specimens, the different effects that influence the compression failure are identified. First damage of fibres occurs always in 0°-ply. Fibre shear failure leads to local microbuckling and the formation and growth of a kink-band as final failure mechanisms. The formation of a kink-band and finally steady state kinking is shifted to higher compressive strains with decreasing ply thickness. Final failure mode in laminates with stress intensification depends on ply thickness. In thick or inner plies, damage initiates as shear failure and fibre buckling into the drilled hole. The kink-band orientation angle is changing with increasing strain. In outer or thin plies shear failure of single fibres is observed as first damage and the kink-band orientation angle is constant until final failure. Decreasing ply thickness increases the unnotched compressive strength. When stress intensifications are present, the position of the 0°-layer is critical for stability under compression and is thus more important than the ply thickness. Central 0°-layers show best results for OHC and CAI strength due to higher bending stiffness and better supporting effect of the adjacent layers.

Bending Performance of Steel/CFRP Plate-Reinforced Core Timber Beams

Experimental study and theoretical analysis on flexural behavior of four core timber beams (one is unreinforced, three are reinforced with steel/CFRP plate) have been conducted. The experimental results show that the bearing capacity of core timber beams reinforced with steel/CFRP (carbon fiber reinforced plastics) plate can be increased by 67.5~97.1% and exhibit higher stiffness, as compared with the unreinforced ones. On this basis, three kinds of failure modes of core timber beams reinforced with steel/CFRP plate are discussed, namely: wood fiber tensile failure, wood fiber compression failure and carbon fiber plate tensile failure. For different failure modes, the compression steel plate yield is considered to derive the formula for calculating the bending capacity of core timber beams reinforced with steel/CFRP plate. The values calculated by the proposed formula are in good agreement with the experimental results, and, thus, can be applied to the engineering practice.