Matrix Breakage Research Articles

Hybridization of thermoplastic/glass fiber reinforced epoxy composites for lightweight structures

Understanding how different hybrid composite designs under flexural, interlaminar shear and fracture is the objective of this study. The hybrid composite was manufactured utilizing the hand-layup process to produce three different laminate arrangements beside the neat composite. The effects of PC integration and position through the hybrid composites were evaluated, and an analysis of the damage mechanisms was performed. The results demonstrated that incorporating the PC sheet resulted in an improvement in overall performance. Additionally, delamination was determined to be the most prevalent type of failure, followed by fiber and matrix breakage and plastic deformation of PC sheet.

Assessment of damage sequence in additive manufactured composite laminates under quasi-static out-of-plane loading

The understanding of the impact behaviour of additive manufactured continuous fibre reinforced polymers must start from the analysis of the damage mechanisms. In this investigation, the impact damage in a 3D-printed continuous carbon fibre reinforced polymer is studied by means of quasi-static indentation tests. The coupons are manufactured with Fused Filament Fabrication (FFF) using a thermoplastic resin. Three indentation displacement levels were tested, analysing different phases of the impact using X-ray Computed Tomography. The effects of fibre orientation were considered, establishing a comparison between one laminate with conventional orientations (0, 90, ±45) and one with disperse orientations. Results show a progressive damage generation influenced by the inherent defects of the manufacturing process, characterized by delamination growth and stiffness reduction. Fibre and matrix breakage only appear at the final stages when the laminate peak load is reached. The considered dispersed laminate shows less delaminated interfaces compared to the conventional one.

Effect of impact and flexural loading on hybrid composite made of kevlar and natural fibers

In this work, four varieties of hybrid Fiber-Reinforced Polymer (FRP) panels made of kevlar-29 and natural fibers are studied. All panels have kevlar-29 face sheets and natural fiber core, such as jute, flax, sisal, and hemp. This research focuses on the behavior of these hybrid FRP panels under flexural and impact loading so that the panels can be explored for the structural/semi-structural members of army shelters, portable helipad, and roofing panels in high-altitude areas. Natural fibers are chemically treated with NaOH to improve hydrophobicity. The panels are vacuum bagged, the fiber volume fraction is 0.39, and the thickness is close to 4 mm. Three-point flexural loading using the universal testing machine and low-velocity impact loading up to 24 J under drop weight impact test setup is carried out to characterize the panels. Damage area, delamination, permanent deformation, indentation depth, energy absorbed, flexural strength, and modulus are measured. The hybrid flax/kevlar panel and hemp/kevlar panel, each resist impact with permanent deformation less than 0.5 mm up to 24 J. Without significant face sheet or core fiber breakage, the delamination is spread over a small radial distance of 18.5 and 24.5 mm, respectively. Interface matrix breakage causes delamination. The load vs deflection curve is almost linear under flexural loading, and specimens failed under compression at 240 MPa. The numerical simulation is also done using ANSYS and LS-DYNA for detailed study.

Mechanical anisotropy associated with beddings in shale under Brazilian test conditions: Insights from acoustic emission statistics

A comprehensive understanding of shale’s bedding anisotropy is crucial for shale-related engineering activities, such as hydraulic fracturing, drilling and underground excavation. In this study, seven Brazilian tests were conducted on shale samples at different bedding orientations with respect to the loading direction (0°, 45° and 90°) and the disc end face (0°, 45° and 90°). An acoustic emission (AE) system was employed to capture the evolution of damage and the temporal-spatial distribution of microcracks under splitting-tensile stress. The results show that the Brazilian tensile strength decreases with increasing bedding inclination with respect to the disc end face, while it increases with the angle between bedding and loading directions. Increasing the bedding inclination with respect to the end face facilitates the reduction in b value and enhances the shale’s resistance to microcrack growth during the loading process. Misalignment between the bedding orientation and the end face suppresses the growth of mixed tensile-shear microcracks, while reducing the bedding angle relative to the loading direction is beneficial for creating mixed tensile-shear and tensile cracks. The observed microscopic failure characteristics are attributed to the competing effects of bedding activation and breakage of shale matrix at different bedding inclinations. The temporal-spatial distribution of microcracks, characterized by AE statistics including the correlation dimension and spatial correlation length, illustrates that the fractal evolution of microcracks is independent of bedding anisotropy, whereas the spatial distribution shows a stronger correlation. The evolution features of correlation dimension and spatial correlation length could be potentially used as precursors for shale splitting failure. These findings may be useful for predicting rock mass instability and analyzing the causes of catastrophic rupture.

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.

Contribution to the Microstructural Study of a Composite Material Based on Carbon Fibers for Use in Orthopedic Prostheses

The use of a carbon fiber composite material to make external prostheses in the form of a femoral socket was the subject of this laboratory study. According to the prior bibliographical studies, this material adapts well to this type of prosthesis. The objective of this research is to study its microscopic structure, in order to verify the good wetting of the fibers by the resin, the good cohesion and molding by infusion. The morphological study of the facies of the parallelepiped-shaped specimens was carried out after cuts perpendicular to the axis of the fiber strands, parallel according to the width and thickness of the specimen. This study was carried out using a scanning electron microscope (SEM), in order to determine, thanks to the typical microstructure of the composite, the various degradations, which appear as a result of the effect of static tension. The laminate used is based on three layers of carbon taffeta fabric and an orthocrylic resin. Tensile tests have been carried out at a speed of 1mm/min with a Zwick/Roell machine with a load cell of 50 kN. This speed was chosen to allow a comparative study with glass fiber specimens, which have been used previously for the production of prostheses, before those made of carbon. The microscopic study allowed to identify the four types of degradation; Matrix fracture, which manifested itself as fault lines, in preferred directions of different sizes. This contributed to interlaminar delamination. The decohesion that contributes to delamination in a different way from that of matrix breakage is visible at different levels. Interlaminar delamination results from the combined effect of matrix breakdown and decohesion and manifests itself as uneven strata. Fiber breakage was manifested by shearing. This study allowed to observing a degradation of the material imposed by static traction. As for the material used in orthopaedics, it has retained good cohesion and meets the requirements of prostheses, despite the defects detected by the microscopic study.

Anisotropic Composition and Mechanical Behavior of a Natural Thin-Walled Composite: Eagle Feather Shaft

Flight feather shafts are outstanding bioinspiration templates due to their unique light weight and their stiff and strong characteristics. As a thin wall of a natural composite beam, the keratinous cortex has evolved anisotropic features to support flight. Here, the anisotropic keratin composition, tensile response, dynamic properties of the cortex, and fracture behaviors of the shafts are clarified. The analysis of Fourier transform infrared (FTIR) spectra indicates that the protein composition of calamus cortex is almost homogeneous. In the middle and distal shafts (rachis), the content of the hydrogen bonds (HBs) and side-chain is the highest within the dorsal cortex and is consistently lower within the lateral wall. The tensile responses, including the properties and dominant damage pattern, are correlated with keratin composition and fiber orientation in the cortex. As for dynamic properties, the storage modulus and damping of the cortex are also anisotropic, corresponding to variation in protein composition and fibrous structure. The fracture behaviors of bent shafts include matrix breakage, fiber dissociation and fiber rupture on compressive dorsal cortex. To clarify, ‘real-time’ damage behaviors, and an integrated analysis between AE signals and fracture morphologies, are performed, indicating that calamus failure results from a straight buckling crack and final fiber rupture. Moreover, in the dorsal and lateral walls of rachis, the matrix breakage initially occurs, and then the propagation of the crack is restrained by ‘ligament-like’ fiber bundles and cross fiber, respectively. Subsequently, the further matrix breakage, interface dissociation and induced fiber rupture in the dorsal cortex result in the final failure.

Effect of hole interaction in the initiation of damage in laminates

In open-hole laminates, when a second hole is made, the stresses and the damage evolution are modified. The main failure mechanisms in laminates subjected to compressive loads are fibre microbuckling and matrix breakage. In this work, the influence of the presence of a second hole in these mechanisms is analysed for two distances between holes. The Serial/Parallel Mixing Theory was used to model the elastic behaviour of the material and a Continuum Damage Model to represent the fibre microbuckling and matrix failure. The equations were implemented in a FEM code developed by the authors. The proposed model has been validated with results from the literature for a laminate with two holes positioned transversally to the applied load. In this problem, it was shown that the growth of the fibre damage is different from that of the matrix.  The laminate is damaged mainly in the zone between the holes. When the distance between holes is reduced, both types of damage around the holes increase.

Low-velocity impact damages of filament-wound composite overwrapped pressure vessel (COPV)

Low-velocity impact tests were carried out on filament-wound composite overwrapped pressure vessel (COPV) specimens at different impact energies and impact points to determine the low-velocity impact damages of wound composite structures. The anti-impact performance of the filament-wound COPV was compared with that of composite laminated and filament-wound composite plates. Different impact damage modes and damage mechanisms inside the wound COPV were investigated through ultrasound scanning, X-ray, and scanning electron microscopy. Results showed that the impact force–time response curve of the wound COPV can be divided into an ascending area, a plateau area, and a descending area. The duration of the plateau area increased with the increase in impact energies. The impact resistance of the filament-wound COPV was the best, followed by that of the composite laminated plate, and the filament-wound composite plate was the worst. The major damage modes of the filament-wound COPV under low-velocity impact included matrix breakage, delamination, and fiber breakage. Delamination in the COPV tube section mainly occurred between the spiral wound and hoop layers. Delamination at the head of the COPV occurred between different winding layers. Fiber breakage inside the COPV mainly developed in the fiber overlapping zone inside the spiral layer. Results indicated that the fiber overlapping zone was the weak part in the filament-wound composite structure.

Monitoring of Plastic Straining Degree of Components Made of Interstitial Free Steel after Uniaxial Tensile Test by the Use of Barkhausen Noise Technique

The usability of the magnetic Barkhausen noise (MBN) technique for monitoring the critical state of plastic straining in the case of interstitial free (IF) steel is demonstrated. IF steels are frequently employed in the automotive industry (e.g., automotive body parts—doors, trunks, wheel arches, etc.), and rupture of components made of these steels occurs during cold forming. Alteration of microstructure expressed in many terms and the corresponding MBN features after the variable degree of plastic strains developed by the uniaxial tensile loading are investigated. It is reported that the effective value of MBN, as well as the shift of MBN envelopes toward higher magnetic fields, can be proposed as the suitable MBN features alerting the incoming matrix breakage. Moreover, the higher MBN in the direction of exerted load at the expense of the perpendicular direction can be found as a result of domain walls realignment.

Development and Characterization of a 3D Printed Cocoa Bean Shell Filled Recycled Polypropylene for Sustainable Composites.

Natural filler-based composites are an environmentally friendly and potentially sustainable alternative to synthetic or plastic counterparts. Recycling polymers and using agro-industrial wastes are measures that help to achieve a circular economy. Thus, this work presents the development and characterization of a 3D printing filament based on recycled polypropylene and cocoa bean shells, which has not been explored yet. The obtained composites were thermally and physically characterized. In addition, the warping effect, mechanical, and morphological analyses were performed on 3D printed specimens. Thermal analysis exhibited decreased thermal stability when cacao bean shell (CBS) particles were added due to their lignocellulosic content. A reduction in both melting enthalpy and crystallinity percentage was identified. This is caused by the increase in the amorphous structures present in the hemicellulose and lignin of the CBS. Mechanical tests showed high dependence of the mechanical properties on the 3D printing raster angle. Tensile strength increased when a raster angle of 0° was used, compared to specimens printed at 90°, due to the load direction. Tensile strength and fracture strain were improved with CBS addition in specimens printed at 90°, and better bonding between adjacent layers was achieved. Electron microscope images identified particle fracture, filler-matrix debonding, and matrix breakage as the central failure mechanisms. These failure mechanisms are attributed to the poor interfacial bonding between the CBS particles and the matrix, which reduced the tensile properties of specimens printed at 0°. On the other hand, the printing process showed that cocoa bean shell particles reduced by 67% the characteristic warping effect of recycled polypropylene during 3D printing, which is advantageous for 3D printing applications of the rPP. Thereby, potential sustainable natural filler composite filaments for 3D printing applications with low density and low cost can be developed, adding value to agro-industrial and plastic wastes.

Numerical study on the dynamic progressive failure due to low-velocity repeated impacts in thin CFRP laminated composite plates

In this paper, the mechanical response of Carbon Fibre Reinforced Polymer (CFRP) plates subjected to repeated low-velocity impacts is numerically investigated. 3D models of composite plates subjected to repeated low-velocity impacts were developed in Abaqus/Explicit software. The numerical models were validated using experimental data obtained from impact tests on CFRP plates using drop weight tower methodology through the comparison of commonly used parameters (i.e., maximum contact force, maximum impactor displacement, and energy absorption). Damage is intended as several modes for intralaminar failure such us fibre or matrix breakage and interlaminar failure (i.e., delamination). Puck failure criterion with linear strain softening was employed for acknowledging intralaminar failure. Additionally, the bi-linear traction–separation cohesive zone model was employed to account for interlaminar damage by defining zero thickness cohesive elements at the interfaces. A sequence of impacts was applied to the composite plate at three different energy levels. It was found that the impact time and the peak force increase in the sequential impacts which indicates a change in the stiffness of the laminate in sequential impacts. The analyses of the results of the damage accumulation and delamination in CFRP plates showed that most of the intra-laminar and interlaminar damage is limited to a few initial impacts in a repeated impact scenario.

A Robust Numerical Methodology for Fatigue Damage Evolution Simulation in Composites.

Composite materials, like metals, are subject to fatigue effects, representing one of the main causes for component collapse in carbon fiber-reinforced polymers. Indeed, when subject to low stress cyclic loading, carbon fiber-reinforced polymers exhibit gradual degradation of the mechanical properties. The numerical simulation of this phenomenon, which can strongly reduce time and costs to market, can be extremely expensive in terms of computational effort since a very high number of static analyses need to be run to take into account the real damage propagation due the fatigue effects. In this paper, a novel cycle jump strategy, named Smart Cycle strategy, is introduced in the numerical model to avoid the simulation of every single cycle and save computational resources. This cycle jump strategy can be seen as an enhancement of the empirical model proposed by Shokrieh and Lessard for the evaluation of the fatigue-induced strength and stiffness degradation. Indeed, the Smart Cycle allows quickly obtaining a preliminary assessment of the fatigue behavior of composite structures. It is based on the hypothesis that the stress redistribution, due to the fatigue-induced gradual degradation of the material properties, can be neglected until sudden fiber and/or matrix damage is verified at element/lamina level. The numerical procedure has been implemented in the commercial finite element code ANSYS MECHANICAL, by means of Ansys Parametric Design Languages (APDL). Briefly, the Smart Cycle routine is able to predict cycles where fatigue failure criteria are likely to be satisfied and to limit the numerical simulation to these cycles where a consistent damage propagation in terms of fiber and matrix breakage is expected. The proposed numerical strategy was preliminarily validated, in the frame of this research study, on 30° fiber-oriented unidirectional coupons subjected to tensile–tensile fatigue loading conditions. The numerical results were compared with literature experimental data in terms of number of cycles at failure for different percentage of the static strength. Lastly, in order to assess its potential in terms of computational time saving on more complex structures and different loading conditions, the proposed numerical approach was used to investigate the fatigue behavior of a cross-ply open-hole composite panel under tension–tension fatigue loading conditions.

Hygrothermal aging effects on the mechanical properties of 3D printed composites with different stacking sequence of continuous glass fiber layers

The present work studied the effects of hygrothermal aging on the flexure behaviors of 3D printed composites reinforced with continuous glass fibers. Composites filled with different stacking sequence of continuous glass fiber layers were prepared. Printed laminated composites were subjected to the hygrothermal environment for up to 30 days. Moisture absorption processes and the corresponded microstructure changes were monitored along with the flexural responses of specimens. Multi-scale morphological investigation was applied to reveal the underlying deformation and failure mechanisms of the specimens under flexion with the consideration of different staking sequence of continuous glass fiber layers. The results showed that the evolution of mechanical properties induced by hygrothermal aging was influenced by the competition of different mechanisms. Polyamide matrix crystallization and the elimination of partial residual stress provided the strengthening effect, while the loss of intralayer and interlayer bonding as well as breakage of glass fiber and matrix weakened the mechanical properties of printed composites. The flexural behaviors of composites with separated distribution of continuous glass fiber layers exhibited higher hygrothermal stability in the early stage of aging. However, this advantage weakened with increasing aging time due to gradual delamination between glass fiber layer and matrix layer.

Conversion of Lignocellulosic Sugarcane Bagasse Waste into Bioethanol Using Indigenous Yeast Strain

The article explores a novel way towards effective utilization of solid waste generated from sugarcane bagasse towards maximum energy extraction. Adopting acid treatment coupled with steam explosion deconstructed the hemicelluloses and lignocellulosic material maximizing the fermentable sugar production. The pretreatment of bagasse was optimized with respect to sulphuric acid dosage and steam explosion period. Sugarcane bagasse being source of second generation feedstock proved its capability in bioethanol production based on the effectiveness of pretreatment process. The fermentation of bagasse was carried out at an initial pH 4.5 using indigenous yeast strain isolated from the bagasse. The results showed that pretreated bagasses produced a fermentable sugar of 74±3 g/l. The bioethanol production was found to be 34±2 g/l during a fermentation period of 36 h. Steam exploded acid bagasse led to the efficient breakage of hemicelluloses and lignocellulosic matrix, thus paving the way for scaling-up towards bioethanol production at industrial level.

Assessment of the Length and Depth of Delamination-Type Defects Using Ultrasonic Guided Waves

Fiber-reinforced composite laminates are being increasingly used in various engineering components in the sectors of aerospace and green energy. Due to impacts throughout the service life of the structure, matrix breakage and delaminations significantly altering the structural integrity of the laminate can occur. Hence, robust guided wave structural health monitoring systems are required to ensure continuous safety of engineering structures. In this paper, the ultrasonic method based on the analysis of A0 mode reflecting within the defected area has been proposed to extract the length and the depth of the delamination-type defect. The technique proposed in this study extracts the depth of the damage by analyzing the magnitude variations of direct A0 mode which are caused by the difference of wave velocities in the upper and lower sub-laminates. This results in an altering and frequency-dependent forward-scattered amplitude of direct A0 mode. Furthermore, the proposed approach uses previously obtained information about the depth of the defect, which allows for the determination of the phase velocities of A0 and S0 modes in the upper and lower sub-laminates. As a result, the accuracy of the damage length estimation is increased. The performance of the proposed method was proven with 2D and 3D numerical simulations and experiments on samples with artificial defects. The method validation results showed that the proposed method with some limitations is capable of extracting the length of delamination with an approximate error below 6%.

Finite Element Analysis and Comparison of the Machinability of SiCp/Al Composite and CNT/Al Composite

Metal matrix composites are widely used in aerospace and automotive industries due to their extraordinarily attractive physical and mechanical behavior. In order to compare the machining property of SiCp/Al composite and CNT/Al composite, the two-dimensional orthogonal cutting finite element models were developed by the finite element analysis software ABAQUS/Explicit. The comparison of SiCp/Al composite and CNT/Al composite on the basis of surface quality, sub-surface damage and edge quality was tried out in order to know the machinability of two materials. The results show that the machined surface defects such as small pits, large voids, tear of the matrix and particle breakage are commonly observed during machining of SiCp/Al composite, and the surface residual stress changes from compressive stress to tensile stress. However, there are some large holes, bulges matrix fracture and particle fracture on the machined surface of CNT/Al composite, and the residual stress is mainly compressive stress. Therefore, at the equal reinforcement effect, the machinability of CNT/Al composite is better than that of SiCp/Al composite.

Green Synthesis of Aluminium Oxide Nanoparticles and its Applications in Mechanical and Thermal Stability of Hybrid Natural Composites

In the current scenario, biosynthesis has a major trend in the world due to its eco-friendly approach, effectiveness and low cost. In this experiment Aluminium Oxide nano powder was extracted from ‘Muntingia Calabura’ leaf with aluminium nitrate as precursor. An attempt has been made to develop the properties of sisal/coir, sisal/banana and banana/coir based hybrid composite with addition of aluminium oxide (Al2O3) nano powder. Compression moulding technique was adapted to fabricate the epoxy based natural fiber composites. Nano Al2O3 powder was added in 0, 1, 2 and 3 wt%. The results demonstrate that addition of nano powder up to 3 weight (wt) percentage improvise the tensile, flexural and impact properties for all incorporated hybrid fibers. Residual wt% for sisal/coir, sisal/banana and banana/coir hybrid composites enhanced from 27.15 to 29.14, 26.07 to 31.33% and 23.76 to 27.50% by 3% nano substitution. Degradation temperature improved in different stages of hybrid combinations. Scanning electron microscope (SEM) images clearly showed the reduction of fiber breakage, matrix breakage and void gaps due to alumina nano powder addition.

Updating the probability of failure of rock wedges

In hard rock masses, discontinuities control the slope stability, rather than block matrix breakage. The relative position of joints and slope face defines the most likely mechanisms of failure. Among these mechanisms, the wedge failure is one of the most common ways of failure in which joint sets dip and dip direction, slope geometry and direction, external forces (including water pressure and earthquake) and rock and joints mechanical properties control the stability. The determination of these input parameters is not straightforward, mainly due to their variability and the limited amount of information available. Besides, in most projects, input parameters come from different sources (e.g., expert opinion, back-calculation, laboratory tests, field test or different project stages). Therefore, this limited information from different sources should be appropriately incorporated into the stability analysis to assist the design and decision-making process. In this context, random sets arise as a powerful tool to combine different sources of information and to perform a reliability assessment under limited information. This feature makes it possible to update the probability of failure as new evidence is available. With this framework, this paper presents a reliability assessment of wedge stability in a rock slope of a sandstone quarry, located in Une Cundinamarca, where information on mechanical and geometrical parameters has been collected for 20 years.

Cross-Influence between Intra-Laminar Damages and Fibre Bridging at the Skin-Stringer Interface in Stiffened Composite Panels under Compression.

In this paper, the skin–stringer separation phenomenon that occurs in stiffened composite panels under compression is numerically studied. Since the mode I fracture toughness and, consequently, the skin–stringer separation can be influenced by the fibre bridging phenomenon at the skin–stringer interface, in this study, comparisons among three different material systems with different fibre bridging sensitivities have been carried out. Indeed, a reference material system has been compared, in terms of toughness performance, against two materials with different degrees of sensitivity to fibre bridging. A robust numerical procedure for the delamination assessment has been used to mimic the skin–stringer separation. When analysing the global compressive behaviour of the stiffened panel, intra-laminar damages have been considered in conjunction with skin–stringer debonding to evaluate the effect of the fibre and matrix breakage on the separation between the skin and the stringer for the three analysed material systems. The latter are characterised by different toughness characteristics and fibre bridging sensitivities, resulting in a different material toughness.