Fiber Failure Research Articles

Local strain quantification of a porous carbon fiber network material

While porous materials’ wide range of attractive functional properties have led to their development for a variety of applications, their intrinsically stochastic microstructures prevent straightforward approaches to predicting their mechanical behavior. This is attributed to the mechanisms that govern the macroscale behavior of these materials operating on multiple microstructure-specific length scales spanning several orders of magnitude. The goal of this work was to experimentally observe these operative deformation mechanisms to better improve the development of mechanism-informed models that more accurately predict the behavior of these materials. In this study compression tests were conducted on a porous carbon fiber network material. The resulting macroscale mechanical properties and mesoscale deformation behavior were tied together through digital image correlation (DIC) strain mapping. It was shown that deformation accumulation occurred via both reversible (fiber bending and sliding) and irreversible (fiber and junction failure) ways. The presence of irreversible deformation is indicated by strain being retained after unloading, with values of up to 0.426 locally and 0.248 globally. Local and macroscopic recovery of up to 0.306 and 0.207 strain respectively showcase the operation of reversible deformation. Furthermore, the calculation of energy loss coefficients increasing from 0.016 to 0.371 illustrates that the deformation occurs via dissipative mechanisms.

Comparison of Hashin and Puck criterions for failure behavior of pin loaded composite plates

AbstractIn this study, the failure behavior of carbon fiber‐reinforced pin‐jointed composite plates were analyzed for different criteria. For this purpose, composite plates with a single and double pin joints were prepared from four layers carbon fiber composites. The effect of pin number, pin position on plate damage load and type was investigated experimentally and numerically under the tensile test. Numerically, progressive damage analysis was performed using Hashin and Puck failure criteria, and the approach rates to the experimental results were determined. It was observed that the experimental results obtained for single pin joint composites and the numerical data obtained using the Puck damage criterion were at least 87 % compatible, and this rate was determined as 85 % for the Hashin failure criterion. For the double pin jointed composites, it was seen that the experimental results and the results of the Puck damage criterion were compatible with at least 90 %, and this rate was obtained as 84 % for the Hashin failure criterion. The dominant damage type seen in the specimen is matrix shear and fiber compression according to the Hashin damage criterion, inter fiber failure in transverse tension for Puck.

Detailed Finite Element Models for the Simulation of the Laser Shock Wave Response of 3D Woven Composites

This paper presents a numerical study on the laser shock wave propagation in a 3D woven carbon-fiber-reinforced polymer (CFRP) material by means of detailed and homogenized finite element (FE) models. The aim of this study is to numerically characterize the shock wave response of the 3D woven CFRP in terms of back-face velocity profiles and the induced damage, and to investigate whether the detailed FE models could be effectively replaced by homogenized FE models. The 3D woven geometry was designed using the TexGen 3.13.1 software, while the numerical analyses were executed using the R11.0.0 LS-Dyna explicit FE software. A high-strain-rate behavior was considered for the matrix. The fiber bundles in the detailed models were modeled as a high-fiber-content unidirectional composite laminate, with its mechanical properties calculated by micromechanical equations. A progressive damage material model was applied to both the fiber bundles of the detailed model and the homogenized models. The results of the detailed model reveal a considerable effect of the material’s architecture on the shock wave propagation and sensitivity of the back-face velocity profile to the spot location. Consequently, the homogenized model is not capable of accurately simulating the shock wave response of the 3D woven composite. Moreover, the detailed model predicts matrix cracking in the resin-rich areas and in the bundles with high accuracy, as well as fiber failure. On the contrary, the homogenized model predicts matrix cracking in the same areas and no fiber failure.

Damage-tolerance design method for composite high-pressure hydrogen vessels of fuel cell vehicles and stacking-sequence optimization method based on the design method

An approach was proposed to design high-pressure composite hydrogen vessels for fuel cell vehicles with damage tolerance. In addition, a stacking-sequence optimization method was developed, which was built upon the damage tolerance design. A no-growth approach, damage categorization, and residual strength requirements were proposed for the damage-tolerance design method for high-pressure hydrogen vessels, which were implemented in the damage-tolerance design method for composite aircrafts. The initial burst pressure was set at 180% of normal working pressure (NWP) assuming that the structural health monitoring (SHM) system with acoustic emission (AE) testing would immediately detect the occurrence of fiber failure. Stacking-sequence optimization was then conducted to minimize vessel thickness and meet the residual strength requirements. As a result of the optimization, the calculations confirmed that the vessel thickness could be reduced by approximately 52% of the existing vessel stacking sequence. The results show that the thickness of the vessel can be reduced by introducing a damage-tolerant design. Moreover, the proposed method for an optimal design based on the damage-tolerance design method is effective.

A High-Capacity Optical Metro Access Network: Efficiently Recovering Fiber Failures with Robust Switching and Centralized Optical Line Terminal.

This study proposes and presents a new central office (CO) for the optical metro access network (OMAN) with an affordable and distinctive switching system. The CO's foundation is built upon a novel optical multicarrier (OMC) generation technique. This technique provides numerous frequency carriers that are characterized by a high tone-to-noise ratio (TNR) of 40 dB and minimal amplitude excursions. The purpose is to accommodate multiple users at the optical network unit side in the optical metropolitan area network (OMAN). The OMC generation is achieved through a cascaded configuration involving a single phase and two Mach Zehnder modulators without incorporating optical or electrical amplifiers or filters. The proposed OMC is installed in the CO of the OMAN to support the 1.2 Tbps downlink and 600 Gbps uplink transmission, with practical bit error rate (BER) ranges from 10-3 to 10-13 for the downlink and 10-6 to 10-14 for the uplink transmission. Furthermore, in the OMAN's context, optical fiber failure is a main issue. Therefore, we have proposed a possible solution for ensuring uninterrupted communication without any disturbance in various scenarios of main optical fiber failures. This demonstrates how this novel CO can rapidly recover transmission failures through robust switching a and centralized OLT. The proposed system is intended to provide users with a reliable and affordable service while maintaining high-quality transmission rates.

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.

Biaxial fatigue failure of short glass fiber reinforced polyamide 6,6: An in-depth investigation of stiffness drop and microstructural evolution

In the automotive industry, short glass fiber-reinforced thermoplastics are widely used under the hood and subjected to dynamic vibrations of the engine in multiple directions resulting in fatigue failure. Under fatigue loading, a significant portion of the strain energy is stored within the material, while the remaining portion is lost due to internal frictions and the damage occurrence. Internal friction results in heat generation, which in turn causes an increase in external temperature. This increase in temperature leads to thermal degradation of the polymer. Investigations on the cause of the stiffness drop are not widely available in the literature. Therefore, this study explores the source of the stiffness drop under biaxial fatigue loading of a polyamide 6,6 reinforced with 30 wt. % short glass fibers (PA66GF30) and distinguishes the contributions of thermal degradation and damage accumulation. The thermal evolution of the specimens was captured by means of thermography. In addition, the digital image correlation (DIC) technique was used to measure the in situ strain field during the fatigue. Despite the temperature stabilization being observed around the 10,000th cycle, the reduction in the stiffness continued until failure which was attributed to the mechanical damage accumulation and cyclic creep during the fatigue tests. Dynamic mechanical analyses (DMA) were carried out to quantify the stiffness drop with the varying temperature. From the results, it is seen that the damage accumulation and cyclic creep during the fatigue tests were responsible for the major part of the stiffness drop. Finally, scanning electron microscopy (SEM) inspection of the fracture surface was performed to identify fatigue damage mechanisms. Four unique features associated with the fatigue damage were identified: (1) debonding of fibers from the matrix, (2) polymer matrix crazing, and (3) cavitation and porosities, (4) pull out fiber ends and break on the fiber.

Influence of co-deposition modification on mode I and II interlaminar toughness of epoxy laminates interleaved with waste textiles using experimental measurement and finite element technique

Interlaminar delamination has been a persistent problem that restricts the ability of fiber reinforced laminated composites under applied load. The influence of polyethyleneimine-catechol (PEI-CCh) co-deposition modification on the mode I (GIC) and II interlaminar fracture toughness (GIIC) of plain glass fiber fabric reinforced epoxy composites (PGFRECs) were discussed using double cantilever beam (DCB) and end notch flexural (ENF) tests. It was found that interfacial properties of PET/epoxy and PET/cotton/epoxy interfaces were substantially improved after co-deposited modification, which laid a solid foundation for enhancing the resistance to interlaminar delamination. GIC and GIIC in platform of crack propagation greatly increased with the introduction of co-deposition layer. The fracture surfaces of delaminated failure specimens were observed by scanning electron microscope. The higher propagation fracture toughness for co-deposition modified PGFRECs is due to the anchoring effect of functional layer combining waste fabrics with epoxy matrix to provide favorable stress transfer channel prior to macroscopic crack formation. In regard to the delamination crack, new crack generation and bridge fiber failure mainly dominated the mode I crack extension process, while zigzag sections were particularly common for mode II fracture specimens.

Prediction of fatigue limit stress in C/SiC composites: Effect of stochastic load spectrum

AbstractUnder cyclic‐fatigue loading, stochastic loading may occur and affect the fatigue limit stress (FLS) in C/SiC composites. In this paper, the FLSs in different C/SiC composites were predicted considering stochastic loading spectrums. Damage mechanisms of interface wear and fibers failure were considered in the global load sharing criterion to determine the fracture life and fiber's failure probability in three different stochastic loading spectrums, that is, constant, increasing and decreasing stochastic stress spectrum. Experimental FLS and fatigue life degradation rate were predicted using the developed micromechanical approach, and the effect of cyclic duration under stochastic spectrums on the FLS was analyzed. Relationships among the FLS, life degradation rate, stochastic spectrum, and cyclic duration were established.

Shear performance and size effect of CFRP strengthened RC beams

In this study, a 3D meso-scale numerical simulation method is established for analyzing the shear failure of carbon fiber reinforced polymer (CFRP) strengthened RC beams without stirrups. The inhomogeneity of concrete, the bond-slip relationship between steel bars and concrete, and the interaction between CFRP and concrete are considered. Based on this method, effects of shear-span ratio and CFRP fiber ratio on the shear performance and nominal shear strength size effect of CFRP strengthened RC beams are investigated. Results indicate that the size effect of CFRP strengthened RC beams is obvious, however, the shear-span ratio has little impact on the size effect of nominal shear strength of RC beams. The CFRP fiber ratio enhances the shear strength of RC beams on the one hand, while weakens the shear size effect of RC beams on the other hand. However, its influence on the shear performance of RC beams remains basically unchanged with varying shear-span ratios, indicating that there is no coupling effect between the shear-span ratio and CFRP fiber ratio. The shear-span ratio significantly influences both the shear bearing capacity of RC beams and the shear contribution of CFRP sheets, with the increase in the shear-span ratio, the shear bearing capacity of RC beams decreases to varying degrees, and the shear contribution of CFRP sheets increases initially and then decreases. Finally, the shear strength size effect law (SEL) of CFRP strengthened RC beams is proposed, which can quantitatively describe the effects of the shear-span ratio and the CFRP fiber ratio.

Pseudo-ductile behaviour of fibrous composite Z-pins

This paper describes the development and characterisation of a novel type of composite Z-pin able to accommodate large deformation without exhibiting fibre failure. Three types of pseudo-ductile Z-pins are fabricated by means of micro-pultrusion of polybenzoxazole (PBO) fibres. Namely, unidirectional PBO fibre (uPBO) Z-pins in combination with a ductile (uPBO/DCT) and a brittle (uPBO/BT) matrix system are developed, together with a twisted PBO fibre Z-pin in combination with a ductile matrix (tPBO/DCT). Single pin bridging tests are carried out across the full mode mixity range from mode I (Φ = 0) to mode II (Φ = 1). The tests reveal that uPBO-based pins are able to pull out throughout the full mode mixity range, regardless of the ductility of the pin matrix. uPBO/DCT pins exhibit a 20-fold increase in energy dissipation per pin than traditional carbon fibre/bismaleimide (CF/BMI) pins at load mode mixities higher than Φ = 0.9. The mode I behaviour of all pins considered is comparable. All PBO pins exhibit an apparent delamination toughness enhancement superior to CF/BMI at mode mixities above Φ = 0.2, with a ductile matrix increasing the average energy dissipated per pin by a further 2–8 %.

Shear Buckling Mode and Failure of Flat Fiber- Reinforced Specimens in the Axial Compression 2. Numerical Method, Experimental and Numerical Investigations of the Specimens with a [0]s Layup

Shear Buckling Mode and Failure of Flat Fiber- Reinforced Specimens in the Axial Compression 2. Numerical Method, Experimental and Numerical Investigations of the Specimens with a [0]s Layup

An analytical model to predict bond behavior of fiber reinforced polymer bonded to concrete with an end anchorage system

The end mechanical anchorage system has been widely applied in the conventional externally bonded reinforcement (EBR) technology, to hinder the premature debonding failure of fiber reinforced polymer (FRP) laminate, especially for the reinforcement structures with prestressed FRP due to higher interfacial shear stress at the ends. Through the introduction of the hinge as the substitution of end anchorage, this paper presents a numerical model based on the bilinear bond-slip model and ordinary differential equations in elastic, elastic-softening, and elastic-softening-debonding stages. The bond behavior of the FRP-concrete interface under the end anchorage in different stages is predicted, obtaining the analytical expressions of interfacial load-slip relation, interfacial shear stress distribution, and the stress distributions of FRP. Additionally, two experimental programs from this group and previous literature were involved in this study to validate the accuracy of the numerical model. The comparison shows they are in good agreement. Moreover, it indicated that the strength increase is linear with the torque applied in the end anchorage, but bonding strength is not the case.

Cut resistance of climbing ropes – A comparative analysis of existing measurement methods and a simulated accident

The cut resistance of climbing ropes remains unsolved despite numerous attempts to address it over the past 20 years. Recently, new laboratory test methods have been developed to evaluate rope performance better. This paper compares the fiber failure modes induced by these tests to those observed after a simulated climbing accident. Characteristic fiber failure modes were identified for each test, depending on the position within the rope’s cross-section. The results show that current laboratory methods do not comprehensively replicate the breaking mechanisms in the sheath and core that can occur during actual climbing accidents. The UIAA 101 test, however, shows the most potential for accurately reproducing failure modes with certain modifications.

A study on fracture behavior of SEN natural hybrid composite specimen under tensile load

In this work, two reinforcements (natural jute fiber and glass fiber) hybridized with different volume fractions, are reinforced with a constant volume epoxy resin through hand layup method. The ASTM standard tensile specimen of jute natural epoxy composite of different volume fractions and orientations of fibers, with varied single edge notch (SEN) size were subjected to uniaxial tensile load in universal testing machine. Effect of jute volume fraction, notch size and fiber orientation on tensile strength and fracture toughness has been studied through experimental results. Increased percent of jute fibre showed decrease in tensile strength and fracture toughness. Also, with the increase in notch size, the tensile strength decreased and the fracture toughness increased. Further, the tensile strength and fracture toughness were superior in 0°/90° fiber orientation specimen than those with ±45° fiber orientation. Furthermore, experimental results were validated by conducting statistical and fractographic analysis. The jute fiber percentage was ranked as best level factor affecting the fracture behavior as per taguchi method. Morphological features of fractured surfaces were analyzed through scanning electron microscopic (SEM) images with respect to nature of jute fiber failure under uniaxial loading conditions.

Progressive Fatigue Modelling of Open-Hole Glass-Fibre Epoxy Laminates

The failure of composite laminates under cyclic fatigue loads is complex, as multiple failure mechanisms are in play at different scales and interact with each other. Predicting the remaining fatigue life as well as the residual capacities of a composite laminate or component is crucial, particularly for safety-critical applications. A progressive fatigue model is proposed to describe the catastrophic failure of open-hole laminates under tensile cyclic fatigue. To represent both intra-laminar and inter-laminar damage, a combination of a continuum damage mechanics model (CDM) and a discrete cohesive zone model (CZM) is implemented in the finite element (FE) software Abaqus. The CDM combines fibre- and matrix-dominated S-N curves with the Palmgren–Miner accumulation rule and Hashin’s residual strength to form a fatigue failure criterion differentiating between fibre failure (FF) and matrix failure (MF). The CZM implemented in this work is the CF20 model proposed by NASA. Fatigue cycling is simulated using an external cycle-jump scheme, where the stiffness degradation is conducted between the FE simulations outside of the implicit solver [90/0] s. Glass fibre reinforced polymer (GFRP) open-hole specimens were tested in tensile cyclic fatigue at a load ratio of 0.1. The experiments were reproduced numerically and the results compared. After calibration of a set of parameters based on one load level, the model was able to reproduce the experimental S-N curve very well, predicting a slope of −0.10, while the experimental value was −0.11. The failure sequence of the laminate was also successfully reproduced. The growth of the split from the hole, and its interaction with inter-laminar delamination, was successfully captured. The proposed approach was able to describe the fatigue failure of an open-hole laminate with a minimal set of material inputs using a simplified fatigue damage model while avoiding convergence issues.

Analysis of debonding mechanism and concrete cover failure of steel and steel fibre reinforced concrete composite beams

To solve the construction problems of steel reinforced concrete structures, the rebar cage was replaced by steel fibres, thus an innovative structure, steel and steel fibre reinforced concrete (SSFRC) structure, was proposed. Based on the four-point bending tests and numerical modelling of 18 SSFRC beams, the debonding mechanism and concrete cover failure were investigated. The results reflected that SSFRC beams experienced shearing failure, debonding failure and bending failure. Bonding cracks existed in most specimens, and the generation of abundant bonding cracks led to the sudden load decrease. The uncoordinated deformation between concrete cover and top flange appeared during the internal force transmission, making the bonding interface between them resist strong tensile stress and resulting in the debonding failure. After the chemical bond force at the bonding interface failed, the lateral concrete cover was firstly torn at the top flange tip, forming bonding cracks. The trapezoidal failure zone would form in the pure bending zone if bonding cracks developed sufficiently. Increasing the amount of steel fibres could prevent the trapezoidal failure zone from separation. Influenced by debonding failure, the extrusion action between bottom flange and bottom concrete cover was aggravated, generating longitudinal splitting cracks on the bottom surface of specimen.

High-ductility basalt fiber reinforced cement composite with low CO2 emission by interface property transformation: Hydrogen bond transformed into covalent bond

Despite the beneficial features and reduced carbon footprint afforded by basalt fibers, the widespread use of basalt fiber-reinforced cement composite (BFRCC) has issues linked to decreased compressive strength beyond 28 days and insufficient toughness. This study aims to address these constraints by changing the chemical bonding between basalt fibers and the cement matrix from hydrogen bonds to covalent bonds via the use of a surface modification. In accordance with the results, a concentration of 2.5 % of the modifier yields the greatest improvement. The 2.5 % modified BFRCC has a compressive strength 1.88 times that of unmodified BFRCC and an elastic modulus 2.02 times that of unmodified BFRCC. Tensile strength and peak tensile strain are improved by 1.95 times and 2.99 times, respectively. The increased threshold for fracture initiation and the increased energy required for crack propagation are both attributable to the more uniform strain distribution within the improved BFRCC, which allows for higher load sharing. The weakening of the chemical bonds aids in reducing “Z”-type fiber failure. In comparison with conventional BFRCC, the use of modified BFRCC contributes to reducing reductions in cement consumption and greenhouse gas emissions.

Numerical study of the axial compression strength for nano-reinforced filament-wound riser considering curing residual stress

The present study is dedicated to the numerical analysis of progressive failure damage in multiangle nano-reinforced filament wound risers, with due consideration for process-induced residual stresses. Utilizing a multi-model coupling strategy, we introduce an integrated methodology predicated upon the time-varying material characteristics at a macroscopic scale. Initially, the process-induced residual stresses are anticipated via a sequential coupled numerical simulation methodology based on the time-varying attributes of the material. Subsequently, the curing residual stresses serve as the initial stress for the composite wound riser to prognosticate its axial compressive strength, grounded in the progressive damage model. Finally, the multiparametric effects on the strength properties of the composite risers are further investigated to reveal the intrinsic mechanism. The numerical findings evince that curing-induced residual stress retards both fiber and matrix failure while augmenting the axial compressive strength of the composite riser. Furthermore, the escalation in nanoparticle content diminishes the process-induced residual stresses. Additionally, the incorporation of 5 % nanoparticles yields an enhancement in the strength of the composite risers by approximately 16.26 % relative to those devoid of nanoparticles.

Analysis of fracture state and fatigue life of high modulus carbon fiber wrapped composite barrel

High-modulus Carbon Fiber-reinforced Polymer composites are widely used in critical industries due to their exceptional mechanical properties. However, the fatigue and fracture of high modulus carbon fiber materials are currently poorly studied. For this purpose, the NOL ring fatigue tensile testing is referenced and improved to investigate the performance and service life of high-modulus carbon fiber wound barrels. NOL ring specimens, made of M40 carbon fiber material, are subjected to quasi-static tensile and fatigue tests. The fracture state and characteristics of high modulus materials during fatigue are analyzed. Two-parameter Weibull distribution function is used to analysis statistically the fatigue life results of composite samples. Then, the life curve is drawn for different stress amplitudes. Additionally, the fiber fracture surface is observed under a high-power microscope. The fiber fracture model under brittle fracture is established. The results indicate that the fracture characteristics and mechanisms of high-modulus materials differ from those of high-strength materials, necessitating different fatigue life assessment methods. The fatigue failure of high modulus fibers exhibits brittle fracture similar to quasi-static loss, with flat fracture surfaces and minimal cumulative damage. The failure mechanism is accompanied by brittle fractures with a small amount of fiber pulled out.