Fiber Tensile Failure Research Articles

Numerical study on the heat effect on the drilling damage of Ti/CFRP stacks

AbstractCarbon fiber reinforced plastics (CFRP) has strong sensitivity to temperature, as the stacking sequence is titanium alloy (Ti) to CFRP, the damage of CFRP is more severe due to the accumulation of cutting heat. In this study, a stress‐strain constitutive model of CFRP with the effect of thermal stress is proposed. On the basis, a simulation model of drilling Ti/CFRP stacks is established to explore the heat effect on the drilling damage. Based on the results, it can be concluded that the burr of Ti at hole exit is generally low due to the support of CFRP, and the burr height increases by 56.61% as the temperature rises from 182.02 to 355.69 °C. Besides, the intralaminar damage of CFRP is mainly caused by the fiber tensile failure and matrix tensile failure, and the matrix tensile failure is more affected by temperature. Moreover, delamination of CFRP decreases slightly with the reduce of drilling temperature. In addition, serious damage of CFRP on the hole wall usually occurs within the cutting angle of 90° to 135°, and pit defects can be reduced in a lower drilling temperature.Highlights A thermal effect stress‐strain constitutive model of CFRP is proposed. Ti/CFRP drilling model is developed based on the proposed constitutive model. Fiber and matrix tensile failure are main form of intralaminar damage of CFRP. Matrix tensile failure is more sensitive to temperature.

The penetration resistance behavior and corresponding size effects of ultra-high molecular weight polyethylene composite laminates

Focusing on the energy absorption characteristics of ultra-high molecular weight polyethylene (UHMWPE) fiber laminated panels, this study conducts ballistic tests and numerical simulations using 6 mm spherical projectiles to impact the UHMWPE laminated panels. The residual velocity characteristics, energy absorption patterns, and failure modes of the UHMWPE laminated panels under steel ball impacts were analyzed. The results show that the residual velocity of the steel ball increases with the increase of the incident velocity. In the velocity range near the ballistic limit velocity, the residual velocity of the steel ball increases sharply. When the incident velocity exceeds 340 m/s, the increase in residual velocity gradually slows down, tending towards a straight line. When the steel ball velocity is less than 330 m/s, the energy absorption of the UHMWPE laminated panels exhibits linear growth with increasing velocity, with a maximum energy absorption of 47.3 J. In the 327–340 m/s velocity range, the energy absorption of the laminated panels drops sharply from 47 J to around 30 J. In the 340 m/s–600 m/s velocity range, the decline in energy absorption gradually becomes more moderate, decreasing to around 20 J. Beyond 500 m/s, the energy absorbed by the UHMWPE laminated panels stabilizes with increasing velocity, and the fiber tensile failure is the main form of energy absorption of UHMWPE composite laminates under ballistic impact. The failure process of UHMWPE laminated panels presents a multi-stage failure mode, including fiber shear failure, tensile failure, and delamination. As the projectile’s incident velocity increases, the damage mechanism of the UHMWPE laminated panels transitions from tensile-dominated to shear plugging-dominated. Through similarity theory analysis, under certain conditions, the ballistic limit velocity and the dimensionless parameter of unit energy absorption for the UHMWPE laminated panels satisfy geometric similarity.

Experimental and numerical study on the dry/wet burst failure of reinforced thermoplastic pipes

AbstractThis paper investigates the burst failure of reinforced thermoplastic pipes (RTPs) via combined experimental and numerical research. Two completely different burst forms appeared during the experiments. The dry burst form occurs with matrix cracks, fiber breakage and crack of liner and coating, which is a common burst morphology. A new burst morphology, which is never reported in open literature, is observed in the experiments. This burst morphology, defined as wet burst form, presents a long dent in the coating and invisible composite damage. In order to simulate the burst failure of RTPs, a numerical model was proposed, in which element removal criteria and the nonlinear stiffness degradation model based on Hashin‐Yeh failure criterion were employed to conduct progressive failure analysis on 3D composites. It was found that the wet burst form has lower burst pressure and causes larger damaged area, which is more dangerous in engineering. For the damage propagation, progressive failure occurs on middle composites and induces the final burst when the dry burst form occurs. As for the wet burst form, water flows into the middle of RTPs, which causes the delamination, matrix crack and bulge of coating. During the process, fibers play few roles in bearing loads.Highlights The wet burst form of reinforced thermoplastic pipes is firstly observed. Element removal criteria and nonlinear stiffness degradation model were used to simulate the burst failure. The numerical model has a good performance on predicting the burst pressure and damage propagation of composites. The wet burst form has lower burst pressure compared with the dry burst form. Fiber and matrix tensile failure mode are dominant.

Investigation on the bending behaviors of reinforced thermoplastic pipes using a strain energy equivalence method and a continuum damage numerical model

AbstractThis paper investigates the bending stiffness and progressive failure of reinforced thermoplastic pipes (RTPs) under bending loads, in which a theoretical method based on the strain energy equivalence of multi‐layered anisotropic cylinders, is proposed. The bending stiffness and stress field was derived from the equilibrium between the work done by bending moments and the strain energy. This new method could consider the hybrid of isotropic and anisotropic materials and improve computation efficiency significantly. To verify the theoretical method, Abaqus/Explicit quasi‐static analysis on 3D composite elements was performed, in which the progressive failure was considered by using a VUMAT subroutine. The degradation of composites was implemented by a nonlinear stiffness degradation model based on the Hashin‐Yeh failure criterion. The comparison showed that the theoretical results are slightly conservative as the theoretical method neglects the contribution of interlayer interactions. Meanwhile, it can accurately predict the dominant stresses of each composite lamina. According to numerical simulations, the fiber tensile failure, the matrix tensile and compressive failure are the dominant failure modes of RTPs under bending loads. Furthermore, the effects of the winding angles of fibers on damage propagation and the effects of the initial ovality on the bending stiffness are also discussed.

Efficient and Validated Framework for Probabilistic Progressive Failure Analysis of Composite Laminates

In this paper, a finite element-based framework is presented to model the probabilistic progressive failure of fiber-reinforced composite laminates with high fidelity and efficiency. The framework is based on the semidiscrete modeling approach that can be seen as a good compromise between continuum and discrete methods. The enhanced semidiscrete damage model (ESD2M) tool set comprises a smart meshing strategy with failure mode separation, a new version of the enhanced Schapery theory with a novel generalized mixed-mode law, and a novel probabilistic modeling strategy. These three joined components make the model efficient in capturing failure modes such as matrix cracks, fiber tensile failure, and delamination, as well as their interactions with high fidelity, while taking material nonuniformities into account. The model capabilities are demonstrated using single-edge notched tensile cross-ply laminates as an example. The ESD2M was not only capable of capturing the complex damage progression but also provided insights and explanations for some of the failure events observed in the laboratory. The presented framework efficiently integrates failure mode predictions with probabilistic modeling and enables Monte Carlo simulations to predict the ultimate failure strength with good accuracy, as well as its scatter.

An efficient hyper-elastic model for the preforming simulation of Carbon-Kevlar hybrid woven reinforcement

An efficient hyper-elastic model that can reflect the primary mechanical behaviors of Carbon-Kevlar hybrid woven reinforcement was developed and implemented with VUMAT constitutive code for preforming simulation. The model parameters were accurately determined through the uniaxial and bias-extension tests. To calibrate the simulation code, preforming experiments of hybrid woven reinforcement over the hemisphere mold and tetrahedron mold were respectively conducted to validate the proposed hyper-elastic model. The comparison between the simulations and experiments shows that the model can not only accurately capture shear angle distribution and geometry shape after deformation, but also accurately predict the force–displacement curve and potential fiber tensile failure during the preforming process. This result indicates that the proposed model can be used to predict the preforming behavior of Carbon-Kevlar hybrid woven reinforcement, and simulate its manufacturing process of complicated geometry.

An investigation of deformation and failure mechanisms of fiber-reinforced composites in layered composite armor

This paper aims to study the deformation characteristics and failure mechanisms of fiber-reinforced polymer composites used in layered composite armor under ballistic impact. A Kevlar-29/epoxy composite and an ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced composite backed bilayer ceramic armor were respectively impacted against 7.62 mm APM2 projectiles at several different velocities. The dependence of failure mechanisms on impact velocity was analyzed both experimentally and numerically. Ballistic tests revealed that the Kevlar-29/epoxy composite backed armor displayed a lower perforation velocity than the UHMWPE fiber reinforced composite backed armor. However, under non-perforated impacts, the UHMWPE fiber reinforced composite exhibited a much higher back face deflection (BFD). According to the post-mortem visual and SEM analysis, the failure of the Kevlar-29 fiber was dominated by shear plugging in the front layers and fiber tensile breakage in the rear layers, whereas in the UHMWPE fiber reinforced composite, failure was dominated by shear plugging initiated from the front layers. These results suggest that the UHMWPE panel is more effective in resistant fiber tensile breakage which usually occurs on the back side of the panel. Using the Ls-dyna explicit dynamic finite element (FE) program, the ballistic behavior of a layered armor backed by a hybrid panel with varying mix ratios was studied numerically. The results show that using high tensile resistant fiber in the rear layers can effectively prevent fiber tensile failure and using high shear resistance fiber in the front layers can effectively prevent shear failure. These results are valuable in making the best use of fiber-reinforced composites in advanced armor design.

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.

Progressive Failure Analysis of Laminates with Embedded Wrinkle Defects Based on an Elastoplastic Damage Model.

Out-of-plane wrinkling has a significant influence on the mechanical performance of composite laminates. Numerical simulations were conducted to investigate the progressive failure behavior of fiber-reinforced composite laminates with out-of-plane wrinkle defects subjected to axial compression. To describe the material degradation, a three-dimensional elastoplastic damage model with four damage modes (i.e., fiber tensile failure, matrix failure, fiber kinking/splitting, and delamination) was developed based on the LaRC05 criterion. To improve the computational efficiency in searching for the fracture angle in the matrix failure analysis, a high-efficiency and robust modified algorithm that combines the golden section search method with an inverse interpolation based on an existing study is proposed. The elastoplastic damage model was implemented in the finite-element code Abaqus using a user-defined material subroutine in Abaqus/Explicit. The model was applied to the progressive failure analysis of IM7/8552 composite laminates with out-of-plane wrinkles subjected to axial compressive loading. The numerical results showed that the compressive strength prediction obtained by the elastoplastic damage model is more accurate than that derived with an elastic damage model. The present model can describe the nonlinearity of the laminate during the damage evolution and determine the correct damage locations, which are in good agreement with experimental observations. Furthermore, it was discovered that the plasticity effects should not be neglected in laminates with low wrinkle levels.

High-velocity impact response of CFRP panels reinforced with stiffeners

With a goal of reducing the weight of fan blade containment system for jet engine, the high-velocity impact response of carbon fiber reinforced polymer (CFRP) panels reinforced with stiffeners were tested and analyzed. Ballistic impact tests on stiffened panels have been carried out with cylindrical Ti-6Al-4V projectiles at different velocities (210 m/s, 70 m/s and 90 m/s). Results showed there was a significant influence observed due to different impact velocities on the response of the panel skin and the stiffener, and the middle stiffener played an important role in impact energy absorption. Numerical simulations were conducted to provide further insight into the target response by employing a user subroutine VUMAT with revised Hou criteria in commercial finite element (FE) software ABAQUS. The stiffened CFRP panel was found to possess a 14% higher critical penetrating velocity than the CFRP laminated plates with same mass by using validated FE models. Combining with detailed discussion of high-velocity penetration process, the energy absorption mechanism of the stiffened panel under high-velocity impact was analyzed, indicating that the improvement on high-velocity impact response is due indirectly to structural alteration induced better energy absorption by less punch-shear laminate breakage and more fiber tensile failure.

Simulation Study of the Effect of Projectile Length-Diameter Ratio on Anti-Penetration Performance of Composite Armor

We studied the failure modes of 55 g cylindrical projectile penetrating ceramic/titanium alloy/gap/polyethylene/gap/921A steel composite armor structure by numerical simulation, obtained the influence of projectile length-diameter ratio on the anti-penetration performance of structure by analysis. The results showed that, ceramic breaks in-plane and forms ceramic cone, titanium alloy target shows shear failure and bending deformation, 921A steel target shows adiabatic shear failure mode when it is penetrated, bulging when it is not penetrated, the front polyethylene target shows compressive shear deformation, the rear polyethylene target shows bending deformation, and fiber tensile failure is the main failure mode, the impact fiber layer has obvious delamination and degumming phenomenon. Under the same mass condition, the larger the length-diameter ratio of the projectile, the smaller the size of the breach and the greater the penetration depth. With the further increase of the length-diameter ratio, the impact of the projectile on the penetration effect is weakened.

Tensile properties of 3D multi-layer wrapping braided composite: Progressive damage analysis

An experimental and numerical study on mechanical properties and damage behavior of 3D multi-layer wrapping braided composite under axial tensile load is presented. The braiding process of this material is introduced and its tensile properties are obtained in tensile tests. Numerical simulations employ periodical boundary conditions, with interface elements between yarns and matrix added to improve the accuracy of prediction. 3D Hashin-type criteria and Von-Mises stress criterion are employed as damage initiation criteria for yarns and matrix, respectively. The obtained numerical results show a good agreement with the experimental data. The load-bearing capacity and failure mechanisms of 3D multi-layer wrapping braided composites under axial tensile loading are also discussed. A stress distribution shows that the axial yarns are the main load-bearing component of the composite. The main failure mode of the yarns is the yarn-matrix tensile cracking in the width direction, followed by the yarn-matrix tensile cracking in the thickness direction and fibre tensile failure. When the fibres in axial yarns begin to break, the material loses its load-bearing capacity.

Recycling of Commercial E-glass Reinforced Thermoset Composites via Two Temperature Step Pyrolysis to Improve Recovered Fiber Tensile Strength and Failure Strain

Economic and regulatory pressures on the global composites industry have encouraged the research and development of technology for the recycling of fiber reinforced polymer composites. Although significant advancements have been made in the recycling of carbon fiber composites, more progress is needed in the recovery of glass fibers, which make up the overwhelming volume of the composites market. In this study, wind turbine blades and automotive sheet moulding compound (SMC) were subjected to a two temperature step pyrolysis. This multistep process yielded improvements in the recovered E-glass fiber’s tensile strength, by as much as 19%, and strain to failure, by as much as 43%, over a single high temperature step pyrolysis. Despite these gains, pre-pyrolysis fiber measurements indicate that pre-existing damage may inherently limit the quality of glass fiber recoverable from pyrolysis without any post processing.

Interlaminar fracture toughness of CFRPs interleaved with stainless steel fibres

Ductile stainless steel fibres were used as interlayers to enhance the interlaminar fracture toughness of carbon fibre reinforced plastics (CFRPs). The stainless steel fibres were placed at the mid-plane of CFRPs either longitudinally or transversely to the crack growth direction. Mechanical properties and fracture toughness of the CFRPs were studied using uniaxial tensile test and double cantilever beam test, respectively. The Young’s modulus and tensile strength of CFRPs remained essentially the same due to the incorporation of steel fibres longitudinally to the loading direction, and decreased slightly for adding steel fibres transversely to the loading direction. Significant improvements in the fracture energy of CFRPs were achieved for adding stainless steel fibres, i.e. the mean fracture propagation energy increased from 482 J/m2 for the control to 2295 J/m2 for CFRPs with transverse steel fibres at a density of 320 filaments/mm. The main toughening mechanisms of the steel fibres were investigated to be extensive steel fibre bridging and tensile failure. A more pronounced toughness increment was observed for adding steel fibres transversely to the crack growth direction due to the additional mechanisms of carbon fibre delamination and breakage.

Research on the Numerical Simulation of the Properties of Bamboo Bundle Glulam

The properties of bamboo bundles Glulam are directly related to the thickness and binding properties of bamboo bundles. In this paper, a three dimension finite element model of bamboo bundles Glulam is established. The model used Hashin criterion and continuous damage mechanics to analyze the failure and damage evolution of bamboo bundles, cohesive zone model to analyze the failure in adhesive layer between bundles. The stress changes in different layers of bamboo bundles at different time under displacement load were studied. Fiber tensile failure of bamboo bundles mainly occurs in two 0° bamboo bundles layers. The stress peak value of 0° bamboo bundles layer reaches 160MPa.There is no tensile failure in the 90° bamboo bundles layer. Cracking occurs in all three adhesive layers, and the first and third adhesive layer occurs before the second layer. The model established is helpful for the design and application of bamboo glulam.

Determination of the crack resistance curve for intralaminar fiber tensile failure mode in polymer composites under high rate loading

This paper presents the determination of the crack resistance curve of the unidirectional carbon-epoxy composite material IM7-8552 for intralaminar fiber tensile failure under dynamic loading. The methodology, proposed by Catalanotti et al. (2014) for quasi-static loading conditions, was enhanced to high rate loading in the order of about 60 s−1. Dynamic tests were performed using a split-Hopkinson tension bar, while quasi-static reference tests were conducted on a standard electromechanical testing machine. Double-edge notched tension specimens of different sizes were tested to obtain the size effect law, which in combination with the concepts of the energy release rate is used to measure the entire crack resistance curve for the fiber tensile failure mode. Digital image correlation is applied to further verify the validity of the experiments performed at both static and dynamic loading. The data reduction methodology applied in this paper is suitable for intralaminar fiber failure modes without significant delamination. Sufficient proof is given that quasi-static fracture mechanics theory can also be used for the data reduction of the dynamic tests. It is shown, that the intralaminar fracture toughness for fiber tensile failure of UD IM7-8552 increases with increasing rate of loading.

Determination of the strain-energy release rate of a composite laminate under high-rate tensile deformation in fibre direction

In order to successfully model design-critical impact loading events on laminated composite structures, the rate-dependency of the composite material has to be correctly reflected. In this context, the rate-dependency of the strain-energy release rate for fibre tensile failure under high-rate loading conditions has not yet been satisfyingly explored. This study employed compact tension specimens consisting of IM7/8552 for dynamic testing on a split-Hopkinson tension bar system. Data reduction was based on the area method. The obtained strain-energy release rate for testing under high-rate conditions was determined to GIc,dynf+=82.0±20.8kJ/m2, exhibiting a salient drop compared to its counterpart obtained under quasi-static loading (GIc,QSf+=195.8±18.0kJ/m2). Analysis of the strain field surrounding the crack tip using digital image correlation (DIC) suggested a more extensive damage zone for testing under quasi-static than for high-rate loading. A fractographic analysis of the specimens did not indicate any pronounced difference in terms of fracture surface morphology across the two loading rate regimes.

On the translaminar fracture toughness of Vectran/epoxy composite material

The mode I fracture toughness associated with fibre tensile failure was investigated for a Vectran/MTM57 composite system. A modified compact tension specimen was designed and manufactured to mitigate compressive and buckling failure due to the low compressive properties which are an inherent characteristic of Vectran fibres. On average, the mode I translaminar fracture toughness for Vectran/MTM57 was found to be approximately 130–145 kJ/m2 for initiation and 250–260 kJ/m2 for propagation. In contrast with other composite systems such as carbon and glass fibre, the fracture toughness of Vectran/MTM57 was found to be relatively higher, with up to 48.26% and 95.27% for initiation and propagation, respectively for some carbon fibre composite system; 9.93% and 68.6% for initiation and propagation, respectively for S2-Glass/epoxy system.

The effect of matrix shear strength on the out-of-plane compressive strength of CFRP cross-ply laminates

The failure mechanism of ‘indirect tension’ is explored for cross-ply IM7/8552 carbon fibre/epoxy laminates subjected to quasi-static, out-of-plane compressive loading. The sensitivity of compressive response to strain rate and to the state of cure is measured, motivated by the hypothesis that the out-of-plane compressive strength is sensitive to the matrix shear strength. A pressure-sensitive film is placed between specimen and loading platen, and reveals that a shear lag zone of reduced compressive traction exists at the periphery of the specimen, giving rise to a size effect in compressive strength. The width of the shear lag zone reduces with increasing shear strength of the matrix. The laminates fail by the indirect tension mechanism: out-of-plane compressive loading generates tension in the fibre direction for each ply and ultimately induces fibre tensile failure. Finite element (FE) simulations and an analytical model are developed to account for the effect of matrix shear strength, specimen geometry, and strain rate on the out-of-plane compressive strength. Both the FE simulations and the analytical model suggest a recipe for increasing the through-thickness compressive strength.