Fiber Failure Research Articles

Numerical Modelling of Hybrid Polymer Composite Frame for Selected Construction Parts and Experimental Validation of Mechanical Properties

This article is a numerical and experimental study of the mechanical properties of different glass, flax and hybrid composites. By utilizing hybrid composites consisting of natural fibers, the aim is to eventually reduce the percentage usage of synthetic or man-made fibers in composites and obtain similar levels of mechanical properties that are offered by composites using synthetic fibers. This in turn would lead to greener composites being utilized. The advantage of which would be the presence of similar mechanical properties as those of composites made from synthetic fibers along with a reduction in the overall weight of components, leading to much more eco-friendly vehicles. Finite element simulations (FEM) of mechanical properties were performed using ANSYS. The FEM simulations and analysis were performed using standards as required. Subsequently, actual beams/frames with a defined geometry were fabricated for applications in automotive body construction. The tensile performance of such frames was also simulated using ANSYS-based models and was experimentally verified. A correlation with the results of the FEM simulations of mechanical properties was established. The maximum tensile strength of 415 MPa was found for sample 1: G-E (glass–epoxy composite) and the minimum strength of 146 MPa was found for sample 2: F-G-E (G-4) (flax–glass–epoxy composite). The trends were similar, as obtained by simulation using ANSYS. A comparison of the results showed the accuracy of the numerical simulation and experimental specimens with a maximum error of about 8.05%. The experimental study of the tensile properties of polymer matrix composites was supplemented with interlaminar shear strength, and a high accuracy was found. Further, the maximum interlaminar shear strength (ILSS) of 18.5 MPa was observed for sample 1: G-E and the minimum ILSS of 17.0 MPa was observed for sample 2: F-G-E (G-4). The internal fractures were analyzed using a computer tomography analyzer (CTAn). Sample 2: F-G-E (G-4) showed significant interlaminar cracking, while sample 1: G-E showed fiber failure through the cross section rather than interlaminar failure. The results indicate a practical solution of a polymer composite frame as a replacement for existing heavier components in a car, thus helping towards weight reduction and fuel efficiency.

Cellulose-mediated mechanical property tuning in small intestinal submucosal matrix to enhance stem cell osteogenic differentiation.

Natural extracellular matrices (ECM) provide a more accurate simulation of the cellular growth environment, making them excellent substrate materials for in vitro cell culture. The porcine small intestinal submucosa (SIS) is one of the most widely used natural ECM that display superior bioactivity. However, decellularization operations often result in fiber breakage and failure to recover mechanical strength in the SIS. In the current study, 2,3-dialdehyde cellulose (DAC) was synthesized and cross-linked with SIS gel to form hydrogels. The introduction of DAC into the SIS matrix resulted in a tunable increase in stiffness, which was instrumental in promoting stem cell adhesion and spreading, crucial factors for osteogenic differentiation. The cytotoxicity assessment confirmed the biocompatibility of the SIS-DAC hydrogels indicating their suitability for prolonged cell culture. Moreover, the degradation rate of the hydrogel could be effectively controlled by adjusting the DAC content, addressing the rapid degradation issue associated with SIS gels. This work confirmed the feasibility of using cellulose derivatives to modulate the mechanical properties of matrix gels and influence cell differentiation which offers a valuable experimental foundation for the development of advanced matrix gels tailored for cell culture and regenerative medicine applications.

Investigation of the Flexural Behavior and Damage Mechanisms of Flax/Cork Sandwich Panels Manufactured by Liquid Thermoplastic Resin

This study investigates the flexural behavior of three sandwich panels composed of an agglomerated cork core and skins made up of cross-ply [0,90]2 flax or glass layers with areal densities of 100 and 300 g/m2. They are designated by SF100, SF300, and SG300, where S, F, and G stand for sandwich material, flax fiber, and glass fiber, respectively. The three sandwich materials were fabricated in a single step using vacuum infusion with the liquid thermoplastic resin Elium®. Specimens of these sandwich materials were subjected to three-point bending tests at five span lengths (80, 100, 150, 200, and 250 mm). Each specimen was equipped with two piezoelectric sensors to record acoustic activity during the bending, facilitating the identification of the main damage mechanisms leading to flexural failure. The acoustic signals were analyzed to first track the initiation and propagation of damage and, second, to correlate these signals with the mechanical behavior of the sandwich materials. The obtained results indicate that SF300 exhibits 60% and 49% higher flexural and shear stiffness, respectively, than SG300. Moreover, a comparison of the specific mechanical properties reveals that SF300 offers the best compromise in terms of the flexural properties. Moreover, the acoustic emission (AE) analysis allowed the identification of the main damage mechanisms, including matrix cracking, fiber failure, fiber/matrix, and core/skin debonding, as well as their chronology during the flexural tests. Three-dimensional micro-tomography reconstructions and scanning electron microscope (SEM) observations were performed to confirm the identified damage mechanisms. Finally, a correlation between these observations and the AE signals is proposed to classify the damage mechanisms according to their corresponding amplitude ranges.

Impact of Defects on Tensile Properties of Ancient and Modern Egyptian Flax Fibers: Multiscale X-Ray Microtomography and Numerical Modeling

Flax fibers, while offering numerous benefits, are susceptible to mechanical weakening due to the presence of kink-bands within their structure. The novelty of this study lies in linking mechanical behavior to fiber morphology and defects at multiple scales by utilizing X-ray microtomography to generate detailed 3D images of elementary flax fibers, enabling the creation of accurate finite element (FE) models for analysis. Aging reduces flax fibers’ strength, so both modern and ancient fibers were analyzed to understand their structural evolution over time. Static X-ray microtomography images were converted into 3D FE models for tensile simulations, and tensile tests provided essential properties for numerical modeling. Morphological analysis for both fiber types revealed that kink-bands contain multiple pores oriented ~45° to the fiber/lumen axis, with ancient fibers showing higher porosity (5.6%) and kink-band density (20.8 mm⁻¹) than modern fibers (3.3% and 16.6 mm⁻¹). SEM images confirmed that the intricate lumen and kink-bands lead to fiber failure under tensile loading. Numerical analysis highlighted higher stress concentrations at the kink-band region, particularly at pores in the kink-band region, which can initiate cracks and lead to rupture.

Effect of Nanofillers on the Flexural Performance of 3D Fibre-Reinforced Composites

The aim of this study is to improve the flexural performance and damage mechanism of nano-filled three-dimensional orthogonal woven E-glass/epoxy composites (3DOWC). The inherent brittleness of epoxy-based 3DOWC leads to the early onset of damage mechanisms such as matrix cracking, fibre-matrix debonding, and fibre failure. To overcome these limitations, epoxy resin has been modified with nano-fillers such as graphene nanoplatelets (GNP) and the novel nanostrength® (NS). The epoxy resin was infused in 3DOWC using VARI with different weight percentages of GNP (0.5, 1.0, and 1.5 wt.%) and NS (2.5, 5.0, and 7.5 wt.%). Three samples in each warp and weft direction of 3DOWC were tested in a three-point bend test. The results showed an increase of 48.4%, 56.2%, and 27.4% in flexural strength, final failure, and energy absorption under warp-loading with 0.5 wt.% GNP, respectively, whereas weft-loaded samples with 1.5 wt.% GNP exhibited 12.0% and 10.5% increases in flexural strength and final failure, respectively. However, 7.5 wt.% NS showed an increase in flexural strength in the warp and weft directions by 36.9% and 39.3%, respectively, and an increase in final failure and energy absorption in the warp direction by 39.4% and 12.3%, respectively. For weft-loaded samples, the final failure increased by 39.3% for the same weight percentage, but there was no significant increase in energy absorption in this direction. Scanning electron microscopy (SEM) of damaged samples revealed that crack reconnection by GNP and fibrils formation and plasticization by NS particles improved the overall flexural performance of 3DOWC.

Fracture toughness of fibre failure modes in laminated composites under dynamic loading

Abstract The fracture toughness regarding fibre tensile failure and fibre compression kinking was measured using compact tension and compact compression specimens on a uniaxial bi-directional electromagnetic Hopkinson bar system. During the dynamic tests, the strain/displacement fields were monitored using the digital image correlation technique with a high-speed camera. Digital and scanning electron microscopy were used to investigate the fracture faces of the tested specimens. The initial fracture toughness for fibre tensile failure under quasi-static and dynamic loading was 166 kJ/m2 and 113 kJ/m2, respectively. For fibre compression kinking, the initial fracture toughness was approximately 120 kJ/m2 for both loading conditions. Less fibre pull-out may be responsible for the decrease in fracture toughness for fibre tensile failure under dynamic loading. Whereas for fibre compression kinking failure, there was no significant difference in the fracture faces of the damaged specimens at different loading rates.

Statistical safety evaluation method for composite high-pressure hydrogen vessels considering stacking sequence effect and fiber strength development rate

We developed a method to evaluate the failure rate (FR) for the cylindrical part of a composite high-pressure hydrogen vessel with arbitrary dimensions, number of layers, and stacking sequences by giving the mean and standard deviation of the fiber strength development rate and the stiffness reduction rate under various damage types. The FR is the rate at which the residual strength of a vessel is below the maximum service pressure (125%NWP). Assuming a case in which the vessel is designed with the damage-tolerance design, the FR was calculated for the case of all-layer matrix cracking (assuming beginning-of-life) and fiber failure in two layers in addition to the matrix cracking (assuming the most severe damage that is tolerable during service). The observations demonstrate the importance of improving the probability of detection for non-destructive testing in ensuring the safety of damage-tolerance-designed vessels after fiber failure. The mean strength of the fibers mainly affected the mean residual strength of the composite high-pressure hydrogen vessels when the dimensions and stacking sequence remained unchanged.

Multi scale systematisation of damage and failure modes of high-pressure hydrogen composite vessels in aviation, Part 1: Methodology

In the development of composite Compressed Gaseous Hydrogen (CGH2) storage vessels the multitude of design, material and manufacturing parameters introduce uncertainties. In addition with complex interacting failure modes such as delamination, matrix and fibre failure high safety margins are needed.The aim of this paper is to enable the decrease of safety margins by developing a fundamental methodology to systematise superimposed loads and their propagation across length scales and load domains to enable the reliability assessment and development of CGH2 vessels in aircraft with high reliability and maximum gravimetric storage density. Therefore, the objectives are to analyse existing development strategies, to derive requirements for a new development approach and to define its underlying logic and procedure. This results in a methodology to systematise potentially occurring load cases, corresponding stresses and resulting failure modes of CGH2 vessels in aircraft along the length scales from the aircraft super-system to the material level.

A novel PDA/POSS transition layer on the surface of UHMWPE fibers by co-depositing to improve the mechanical properties of composites

The surface treatment of ultra-high molecular weight polyethylene (UHMWPE) fibers is one of the key technologies for the application of UHMWPE fibers composites. In this paper, the interface transition layer of polydopamine (PDA) and polyhedral oligomeric silsesquioxane (POSS) co-deposited on the surface of corona pre-treatment fiber fabric is used to the uniform and efficient distribution of loads between the fibers and the resin matrix, especially to significantly improve the flexural modulus of UHMWPE fiber fabric composites. Under 2.5 kW corona pre-treatment, 4 g/L of dopamine hydrochloride and 2 wt% of γ-Aminopropyl triethoxysilane aqueous solution, the impact strength, flexural strength, and modulus of UH-C2.5@PDA/PA2 fiber fabric/epoxy composites are greatly improved to 218.6 kJ/m2, 151.7 MPa, and 7.8 GPa, respectively, which are 72 %, 106 % and 143 % higher than those of the untreated UHMWPE fiber composites. It may be attributed to: (1) the corona pre-treatment of UHMWPE fiber induces larger amount of active sites on fiber surface and higher surface energy, leading to a better wettability and adhesion with the matrix resin; (2) the mechanical interlocking engagement between the fibers and nano-POSS particles effectively prevents fibers extraction from the matrix resin and increases the friction of relative sliding; (3) POSS can strengthen the transition layer. The failure of UHMWPE fiber reinforced composites can be mainly attributed to energy absorption of matrix resin fracture, interface damage and relative sliding between matrix resin and fibers, fiber yield deformation and fiber fracture.

Progressive Damage Model of Carbon-fiber Reinforced Polymer Laminates under Low-velocity Impact Loading

The study quantitatively investigates the mechanical structural behavior and damage mechanisms of composite laminates under low-velocity impacts using Abaqus software. A three-dimensional Puck criterion is utilized to identify the onset of fiber failure and matrix cracking under tensile and compressive loading conditions. Two progressive damage evolution models are implemented to simulate damage propagation during impact. The model also incorporates cohesive elements with a bilinear traction-separation law to represent interlaminar damage. The performance of the model is validated by comparing its predictions against experimental results for a composite laminate with a stacking sequence of [0°3/45°/-45°2/45°/0°3] subjected to different impact energies (2 J, 4 J, and 8 J). Despite a slight reduction in accuracy at higher energy levels, the model effectively predicts forcedisplacement curves and energy absorption. The deviation from experimental results is approximately ±6%. This research offers a basis for enhancing the impact resistance and energy absorption characteristics of composite materials.

Lightning ablation damage and residual bending performances of scarf-repaired composite laminates with copper mesh protection

The copper mesh provides effective lightning strike protection for composite structures, while its efficiency can be compromised in scarf-repaired composite structures. In this study, after verified by test results, a numerical analysis procedure was employed to predict the lightning ablation damage and residual bending performances of scarf-repaired composite laminates with copper mesh protection. Initially, the ablation damage and bending damage mechanisms of good repaired and poor repaired composite laminates were analyzed. Then, the impact of lightning strike attachment position and repair design parameters including overlap length and thickness of adhesive layer on the lighting protection performances was investigated. The results indicate that ablation damage of composite and adhesive materials near the repair area significantly compromises structural integrity and reduces the bending strength. The predominant bending failure mode of scarf-repaired woven composite laminates after lightning strike is fiber failure in warp direction, accompanied by small areas of matrix failure and delamination failure. The reestablishment level of the electrical path varies with overlap length and thickness of adhesive layer, subsequently affecting the ablation damage area and depth. This study can provide a reference for the design and process control of scarf-repair in copper mesh protected composite structures.

Green hybrid composites partially reinforced with flax woven fabric and coconut shell waste-based micro-fillers

This research is focused on hybrid green composites using flax woven fabric in which the matrix phase was further reinforced with coconut shell waste-based cellulosic microparticles as fillers. Mesoscale mechanical models were successfully developed to simulate the tensile properties of such hybrid composites based on hybridization of fibers and biobased materials using epoxy resin. S-glass fabrics with plain, twill and biaxial constructions, were used as the outer layers, while plain-woven flax fabric was used as the middle layer. A high level of agreement was observed between the experimental and predicted values. The static tensile tests were followed by cyclic tensile tests, microscopic analysis of fracture surfaces and dynamic mechanical analysis. The influence of the hybrid fabric geometry and combination with biowaste-based micro cellulosic material was observed to significantly influence the tensile properties determined by both experimental and numerical analysis. Dynamic mechanical analysis also validated the quasistatic measurements. A higher storage modulus and loss modulus were registered for the hybrid composites impregnated with a 1 % bio filler-based matrix. The damping factor (tan delta) was lower for the hybrid composites than for the nonhybrid samples and the control samples from the pure matrix. This difference is attributed to the stronger interface between the fibers and the particle-based matrix, which restricts the molecular mobility and increases the stiffness of the composites. Fractographic images were obtained by scanning electron microscopy (SEM) to study the failure modes and mechanisms of the composite samples. The microparticles were uniformly dispersed in the epoxy resin and thus enabled microcracking rather than macrocracks. The failure mainly occurred due to fiber failure, matrix cracking and delamination. Such hybrid composites are useful for exterior and interior components in automotive applications.

A novel continuum damage evolution model based on the concept of damage driving force for unidirectional composites

A novel damage evolution model for unidirectional (UD) composites is established in this paper in the context of continuum damage mechanics (CDM). It addresses matrix cracking and it is to be applied along with the damage representation established previously. The concept of damage driving force is employed based on the Helmholtz free energy. It is shown that the damage driving force can be partitioned into three parts, resembling closely three conventional modes of fracture, respectively. A damage evolution law is derived accordingly based on the newly obtained expressions of the damage driving force. The fully rationalised Tsai-Wu criterion is employed in the model for predicting the initiation of matrix cracking damage and fibre failure, assisted with the rationalised maximum stress criterion for identifying the damage modes. A mechanism is introduced to describe the unloading behaviour as a part of the proposed model. The predictions were validated against experimental results, showing good agreement with the experiments and demonstrating the capability and effectiveness of the proposed model.

Variability in individual native fibrin fiber mechanics

Fibrin fibers are important structural elements in blood coagulation. They form a mesh network that acts as a scaffold and imparts mechanical strength to the clot. A review of published work measuring the mechanics of fibrin fibers reveals a range of values for fiber extensibility. This study investigates fibrinogen concentration as a variable responsible for variability in fibrin mechanics. It expands previous work to describe the modulus, strain hardening, extensibility, and the force required for fiber failure when fibers are formed with different fibrinogen concentrations using lateral force atomic force microscopy. Analysis of the mechanical properties showed fibers formed from 1 mg ml-1and 2 mg ml-1fibrinogen had significantly different mechanical properties. To help clarify our findings we developed two behavior profiles to describe individual fiber mechanics. The first describes a fiber with low initial modulus and high extensible, that undergoes significant strain hardening, and has moderate strength. Most fibers formed with 1 mg ml-1fibrinogen had this behavior profile. The second profile describes a fiber with a high initial modulus, minimal strain hardening, high strength, and low extensibility. Most fibrin fibers formed with 2 mg ml-1fibrinogen were described by this second profile. In conclusion, we see a range of behaviors from fibers formed from native fibrinogen molecules but various fibrinogen concentrations. Potential differences in fiber formation are investigated with SEM. It is likely this range of behaviors also occursin vivo. Understanding the variability in mechanical properties could contribute to a deeper understanding of pathophysiology of coagulative disorders.

Multi-scale correlation of impact-induced defects in carbon fiber composites using X-ray scattering and machine learning

Impact-induced defects in carbon fiber-reinforced polymers (CFRPs)-spanning from nanometer to macroscopic length scales-can be monitored using an aggregate of X-ray-based methods, but this is impractical in typical field conditions. We report on a low-velocity impacted CFRP, which is mapped using small- and wide-angle X-ray scattering and X-ray computed tomography, and employ machine learning for correlating material parameterizations derived from these techniques. The observed 1 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu$$\\end{document}m to 1 mm-sized defects are parameterized in terms of relative density and fiber orientation indicative of fiber failures (kink bands), and the nanometer sized defects in terms of crystal size and unit cell frustration. The 30 to 300 nm defects are parameterized by a power-law scattering decay, differentiating fractal-like behaviors. We find three spatial domains experimentally and by K-means Clustering: Domains of severe damage (with a visual dent), intact domains (without visual or measurable defects) and a transition domain (defects measurable by X-rays). How the parameters are correlated and how they overlap between the domains are discussed. All parameters are able to point to the detrimental fiber breakage in the severe damage domain, and scattering decay also in the transition domain, for example. How individual parameters determined from one experimental technique can be predicted from that of another is also described.

Fracture Criteria for Matrix and Fibers in Unidirectional Polymeric Composites at Static Loadings

When analyzing the strength of structures made of layered fibrous polymer composite materials; the criteria for failure of a monolayer – a unidirectional reinforced composite – are used. A criterion of strength according to the conditions of matrix fracture is formulated, corresponding to conical limiting surfaces and the lowest destructive loads. The criterion of strength according to the condition of fiber failure, which does not allow the paradox of increasing strength in the region of transition from fiber destruction to matrix failure, is given. Experimental verification of the criteria for volumetric, planar, and one-dimensional loads is carried out. Their better correspondence to empirical data is shown and their advantages in comparison with known criteria are marked. A small number of easily detectable parameters of these criteria contribute to their reliability and stability in strength calculations of composite structural elements.

6827 Pharmacological PPARα Activation In Combination With Ketogenic Nutrition Aggravated Muscle Weakness By Metabolic Failure In Septic Mice

Abstract Disclosure: C. Lauwers: None. M.P. Casaer: None. W. Vankrunkelsven: None. S. Derde: None. I. Derese: None. S. Vander Perre: None. P. Vermeersch: None. G.H. Van Den Berghe: None. L. Langouche: None. Introduction: In septic mice, infusion of ketone bodies (beta-hydroxybutyrate (BHB)) attenuated muscle weakness, a debilitating complication of critical illness. Interestingly, in critically ill children, fasting-induced ketosis also improved outcomes, but in adults ketosis upon fasting was impaired, likely due to suppression of PPARα, a key transcriptional regulator of ketogenesis. In septic mice, pharmacological induction of PPARα by pemafibrate (PF) alone, however, was ineffective in promoting ketosis. Therefore, we here hypothesized that PPARα activation by PF combined with ketogenic nutrition can more effectively induce ketosis and hereby reduce muscle weakness in sepsis. Methods: In a fluid-resuscitated and antibiotic-treated mouse model of prolonged (5 days) sepsis (male C57BL/6J), the impact of PF (1mg/kg/d) combined with 4 types of parenteral nutrition (PN) was studied. Mice were either allocated to PF + total PN (composed of glucose, long-chain triglycerides (LCTs) and amino acids) (TPN, n = 18), PF + TPN with an extra LCT emulsion (TPN + LCTs, n = 18), PF + a pure low dose LCT emulsion (Low LCT, n = 16) or PF + a pure high dose LCT emulsion (High LCT n = 18). Healthy control mice on standard chow served as a reference (HC, n=19). After 5 days of sepsis, ex vivo muscle force (aurora scientific®), plasma BHB and lipids (TG, FFA, LDL- and HDL-cholesterol; commercial assays), and liver gene expression levels were measured. Metabolomics of muscle tissue was assessed by LC-MS and plasma acylcarnitines by LC-MS-MS. Results: Liver PPARα gene expression was higher in all PF-treated mice than in HCs. Compared to HCs, specific muscle force was reduced in all septic mice, but mostly so in both PF + LCT groups (PF + Low LCT: 10.7%, PF + High LCT: 25.0%, PF+TPN + LCTs: 44.6%, PF+TPN: 58.4% of HC: 124.7 mN/mm²; p = 0.0001). PF + TPN + LCTs did not induce ketosis, whereas BHB plasma levels increased 95-fold in the PF + High LCT and 10-fold in the PF + Low LCT group (p < 0.0001 vs. other groups). Glycemia was lower in both PF + LCT groups relative to the other septic mice (PF + Low LCT: 52 mg/dl; PF + High LCT: 80 mg/dl; PF + TPN + LCTs: 108 mg/dl; PF + TPN: 102 mg/dl; p < 0.0001). Compared to the PF + TPN group, plasma lipids and long-chain acylcarnitines were increased in all other septic mice with the highest levels in the PF + High LCT group. Muscular glycolytic intermediates and ATP levels were depleted in both PF + LCT groups in comparison with all other septic mice and HCs. Conclusion: In septic mice, PF-induced PPARα activation combined with TPN, irrespective of the amount of LCTs, was unable to induce ketosis and did not attenuate muscle weakness. By contrast, PF-induced PPARα activation in combination with pure LCTs resulted in ketosis, but aggravated rather than improved muscle weakness, irrespective of the dose. In these groups, metabolic analyses suggested a bioenergetic failure of muscle fibers with an accumulation of plasma lipids. Presentation: 6/1/2024

Structural response of glass fiber-polymer composite bending-active elastica beam under long-term loading conditions

Bending-active elastica beams represent structural members which are initially installed as straight beams and then bent into arched shapes by applying horizontal displacements to one support. Designing such members for permanent structures made of fiber-polymer composites involves complex viscoelastic responses, which have not yet been thoroughly investigated. An experimental investigation of medium-scale bending-active elastica beams, consisting of pultruded glass fiber-polymer composite profiles, was thus conducted to investigate the long-term structural behavior of such members under imposed sustained bending and axial compression. The results revealed that viscoelastic responses are based on an interaction of stress relaxation and creep with their effects increased with increasing bending degree and time of exposure to sustained strains and stresses. The imposed horizontal displacement to one of the supports to maintain the bent beam shape induced sustained bending stresses in the beam. Beneficial relaxation of these stresses occurred with relaxation predicted to reach 12 % during a targeted 50-year design service life. Furthermore, the likelihood of the curved beam exhibiting in-plane deformations under sustained stresses enabled creep to occur simultaneously, with associated in-plane creep deformations and strength reduction. While creep deformations remained insignificant, progressive creep rupture occurred at highest bending degrees, exhibiting sequential creep rupture in the outer combined mat layers, delamination, crack opening and final fiber failure. Creep rupture can be prevented by postponing crack initiation in the combined mat layer beyond the targeted design service life. This can be achieved by limiting the bending degree to 50 % of the bending degree at which short-term crack initiation occurs.

3D mesoscale model of steel fiber reinforced concrete based on equivalent failure of steel fibers

Steel fiber reinforced concrete (SFRC) is widely used in civil engineering. Investigating the mechanical properties and failure mechanisms of SFRC materials using mesoscopic models holds significant theoretical and practical importance. The bond-slip interaction between steel fibers and the cementitious matrix is crucial, yet current computational capabilities struggle to simulate the interactions among the numerous components within concrete containing a large number of steel fibers. This paper establishes an equivalent failure model to replace the bond-slip interaction. Based on this model, a multiphase mesoscopic model (including aggregates, the interfacial transition zone (ITZ), mortar, and steel fibers) is developed to predict the mechanical properties and failure modes of SFRC. The accuracy and validity of the model are verified by comparing the simulation results with the experimental results from four-point bending tests on SFRC beams, focusing on load-displacement curves, failure modes, and crack propagation. The results indicate that under load, the ITZ at the sharp edges of large aggregates in the SFRC beam is the first to be damaged, forming microcracks. Subsequently, these cracks bypass the large particles and propagate towards weaker regions with fewer steel fibers, forming macrocracks. At this stage, the steel fibers take over the load from the cementitious matrix and limit crack propagation. The simulated crack propagation trend and crack width during the loading process of the SFRC multiphase mesoscale model match well with the experimental observations. A higher fiber content can mitigate stress concentration within SFRC beams and enhance the fiber bridging effect, significantly improving the flexural load-bearing capacity and toughness of the beams. A smaller steel fiber inclination angle can effectively inhibit the propagation of vertical cracks, thereby increasing the load-bearing capacity and toughness of SFRC beams and extending the service life of the structure.

Puck 3D-based modeling and validation of progressive failure in instrumented glass fiber-reinforced polypropylene via the split-disk test

This study analyzes the mechanical behavior and damage progression of filament-wound thermoplastic composite rings, focusing on the effects of embedded fiber optic (FO) sensors. Utilizing a split-disk test, the study evaluates both experimental and numerical approaches to examine the impact of FO sensors in glass fiber-reinforced polypropylene composite rings. The split-disk test is employed to measure key mechanical properties such as hoop tensile strength, stiffness and failure strain using strain gauges and 3D Digital Image Correlation (DIC). The research specifically examines two extreme configurations of FO sensor placement: parallel and perpendicular to the reinforced fibers. The objective is to propose sensor integration that minimizes potential negative effects on the material's properties. Both instrumented and non-instrumented samples are analyzed numerically and experimentally. The experimental phase involves detailed mechanical characterization using the split-disk test, while the numerical approach uses a developed UMAT finite element model based on the 3D Puck failure criterion and an element weakening method for progressive failure analysis. The numerical models adopt real microstructural details according to optical microscopic analysis. The study concludes that parallel embedded FO sensors are preferable as they enhance the ultimate strength to failure and avoid creating resin-rich zones near the sensor, thereby improving the overall mechanical performance of the composite rings. The 3D Puck failure criterion combined with the element weakening method provides accurate predictions of fiber failure initiation and growth in the composite rings.