Fiber Responses Research Articles

Mechanical Response and Failure Mechanisms of Natural Bamboo Fiber Reinforced Poly-Benzoxazine Composite Subjected to Split-Hopkinson Tensile Bar Loading.

In this study, chopped natural bamboo fibers were successfully added in the benzoxazine matrix by the hot-pressing method to fabricate environmentally friendly bio-composite. The mechanical behaviors and failure mechanisms of neat benzoxazine matrix and its bamboo fiber composite under different tensile strain rates (quasi-static, 35/s and 110/s) were comparatively investigated using SHTB device (split-Hopkinson tensile bar), high-speed camera, DIC method (digital image correlation), and SEM observation (scanning electron microscopy). The results showed the composite exhibited 30.02% and 25.21% higher strength than that of neat benzoxazine under strain rates of 35/s and 110/s, respectively. However, under quasi-static tensile loading, the tensile strength of the composite was not higher than that of neat benzoxazine. The SEM and high-speed camera images showed the bamboo fibers displayed different reinforcing mechanisms under different strain rates. The chopped bamboo fibers could strengthen the composite effectively under dynamic tensile loadings. However, under quasi-static loading, the tensile strength of the composite was largely determined by the potential defects (such as small bubbles, pores, and fiber agglomerations) in the composite.

Mechanical properties and damage analysis of S-glass: A reactive molecular dynamics study

Glass fibers are widely used as reinforcements in composites for applications ranging from lightweight and damage tolerant structures to protective materials providing high levels of energy absorption during ballistic impact. Understanding the atomistic origin of mechanical response and damage modes under various strain rate loading conditions is important to improve the properties of glass fibers. In this paper, molecular dynamics (MD) simulations with a reactive potential relate the composition of S-glass fiber to the mechanical properties and progressive damage mechanisms. Stress-strain response of Magnesium Aluminosilicate S-glass fiber using our newly developed Mg/Al/Si/O ReaxFF interatomic potential is predicted from 1e7/s to 1e15/s. Overall strain rate dependent modulus and strength data exhibit a characteristic S-shaped curve on a semi-log plot indicating strain rate dependent properties followed by a steep rise in properties at approximately 1e12/s to a strain rate-independent plateau. Detailed analysis of the atomic structure during high strain rate tensile loading provides insight into the dependency of properties on the rate of atomistic reconstruction, suggesting that the characteristic time-to-reconstruct is an important factor governing strain rate-dependent progressive damage. The origin of the higher modulus of S-glass over silica arises from electrostatic interactions associated with Al-O and Mg-O bonds in S-glass. Investigation on Al-O-Mg, Mg-BO/NBO interaction, and Al/Si-O ring structure indicates that the reconstruction of local structure leads to a more ductile-type response and progressive damage evolution in S-glass fiber than silica glass . In addition, we introduce a methodology to construct stress-strain response for low strain rates (1E-3/s) from a series of high strain rate loading to prescribed strain levels followed by stress-relaxation to an equilibrium stress level. The method is computationally efficient, and the results agree with the quasi-static modulus of both S-glass and silica.

Impact behavior of hybrid-fiber reinforced concrete beams

The impact studies on concrete beams are primarily pertaining to the drop hammer impact, and studies involving projectile impacts on reinforced concrete beams are limited. In this research, the response of hybrid fiber reinforced concrete (HFRC) beams under quasi-static loading and the projectile impact was studied. The HFRC was produced using eight concrete mixes having different proportions and combinations of three fiber types (viz. polypropylene, steel, and Kevlar). The HFRC mixes had a total fiber volume fraction of 1.2% and 1.4%. In addition, plain concrete was used as a control. The beams were tested under the impact of hemispherical nose projectile at varying strike velocities. The projectile strike velocity was increased till the perforation of beams. The main flexural reinforcement in beams was provided on the back face. In order to assess the punching resistance of beams, the beams were tested under quasi-static punching load applied using the same projectile employed in impact tests. The use of hybrid fibers improved beams’ quasi-static punching resistance in terms of energy absorption and load–displacement behavior. The hybrid fibers also improved the impact response of beams by reducing damage levels, increasing perforation velocity, and reducing ejected mass. By modifying the earlier proposed model for slabs, the ballistic limit of HFRC beams is also predicted.

Compound Motor Action Potentials During a Modest Nerve Crush.

Nerve crush injury results in axonotmesis, characterized by disruption of axons and their myelin sheaths with relative sparing of the nerve’s connective tissue. Despite the widespread use of crush injury models, no standardized method for producing these lesions has been established. We characterize a crush model in which a narrow forceps is used to induce a modest and controlled compressive injury. The instantaneous compound motor action potential (CMAP) is monitored in situ and in real-time, allowing the characterization of neuromuscular response during and after injury. The tibial nerves of 11 anesthetized rats were surgically isolated. After the placement of electrodes, CMAPs were elicited and registered using a modular-data-acquisition system. Dumont-#5 micro-forceps were instrumented with a force transducer allowing force measurement via a digital sensor. Baseline CMAPs were recorded prior to crush and continued for the duration of the experiment. Nerve crushing commenced by gradually increasing the force applied to the forceps. At a target decrease in CMAP amplitude of 70%–90%, crushing was halted. CMAPs were continually recorded for 5–20 min after the termination of the crushing event. Nerves were then fixed for histological assessment. The following post-crush mean values from 19 trials were reported: peak CMAP amplitude decreased by 81.6% from baseline, duration of crush was 17 sec, rate of applied force was 0.03 N/sec, and maximal applied force was 0.5 N. A variety of agonal phenomena were evident post-lesion. Following the initial decrease in CMAP, 8 of 19 trials demonstrated a partial and transient recovery, followed by a further decline. Thirteen trials exhibited a CMAP amplitude near zero at the end of the recording. Twelve trials demonstrated a superimposed EMG background response during and after the crush event, with disappearance occurring within 4–8 min. Qualitative histology assessment at the lesion site demonstrated a correspondence between CMAP response and partial sparing of nerve fibers. By using a targeted decline in CMAP amplitude as the endpoint, researchers may be able to produce controlled, brief, and reproducible crush injuries. This model can also be used to test interventions aimed at enhancing subsequent regeneration and behavioral recovery.

Low-velocity impact response of MWCNTs toughened CFRP composites: Stacking sequence and temperature effects

Despite impressive specific mechanical properties, carbon fiber reinforced polymer (CFRP) composites are strongly susceptible to impact events due to their low interlaminar fracture toughness which fosters delamination phenomena detrimental to the residual mechanical properties of the laminate. The incorporation of nano-fillers in the neat matrix is a suitable way to improve both Mode I and Mode II CFRP fracture toughness. In view of this, the present work assessed the toughening effect of multi-walled carbon nanotubes (MWCNTs) on the impact and post-impact response of carbon fiber reinforced epoxy composites evaluating the effect of two key design parameters: ply stacking sequence and operating temperature. Two stacking configurations, i.e., cross-ply (CP) and quasi-isotropic (QI), and three testing temperatures, i.e. −40 °C, room temperature and +80 °C, were considered. The results highlighted a higher damage tolerance of QI laminates characterized by a superior residual flexural strength than CP for all impact energies and temperatures. Moreover, the toughening effect played by MWCNTs on QI samples was disclosed for all temperatures with an improvement in the normalized residual flexural strength up to 10%. The enhanced damage tolerance must be ascribed to the bridging effect and the pull-out phenomena provided by CNTs which delay matrix cracks opening and propagation.

Influence of Graphene Oxide Nanoparticles on Bond-Slip Reponses between Fiber and Geopolymer Mortar.

In this study, the influence of graphene oxide nanoparticles on the bond-slip behavior of fiber and fly-ash-based geopolymer paste was examined. Geopolymer paste incorporating a graphene oxide nanoparticle solution was cast in half briquetted specimens and embedded with a fiber. Three types of fiber were used: steel, polypropylene, and basalt. The pullout test was performed at two distinct speeds: 1 mm/s and 3 mm/s. The results showed that the addition of graphene oxide increased the compressive strength of the geopolymer by about 7%. The bond-slip responses of fibers embedded in the geopolymer mixed with graphene oxide exhibited higher peak stress and toughness compared to those embedded in a normal geopolymer. Each fiber type also showed a different mode of failure. Both steel and polypropylene fibers showed full bond-slip responses due to their high ductility. Basalt fiber, on the other hand, because of its brittleness, failed by fiber fracture mode and showed no slip in pullout responses. Both bond strength and toughness were found to be rate-sensitive. The sensitivity was higher in the graphene oxide/geopolymer than in the conventional geopolymer.

Making sense of sensibility: part 1.

Thermal and electric pulp sensibility tests are commonly used by the majority of clinicians when diagnosing endodontic disease. These tests indirectly determine the state of pulpal health by assessing the response of the Aδ nerve fibres within the pulp-dentine complex. A positive response to sensibility testing indicates that the nerve fibres are functioning but does not give any quantitative information on nerve function, pulpal blood flow or histological status of the dental pulp. These tests have inherent limitations, including a reliance on a patient's subjective response to the test and the dentist's interpretation of the patient's response. This two-part series aims to help clinicians to reach an accurate endodontic diagnosis by providing an overview of how to undertake common pulpal sensibility tests correctly, how to interpret their results and understand their limitations. This section provides an overview of pulp testing, definitions of terminology relevant to pulp testing, the diagnostic uses of pulp testing and a summary of the diagnostic accuracy of different pulp tests.

Tuning the lateral response of unbonded fiber reinforced elastomeric isolators (U-FREIs) through horizontal holes: Experimental and numerical findings

Fiber-Reinforced Elastomeric Isolators (FREIs) are elastomeric devices introduced as a low-cost alternative to the well-known Steel-Reinforced Elastomeric Isolators (SREIs). As common in rubber-based devices, the application of FREIs to lightweight structures is challenging as slender bearings tend to be unstable under large horizontal displacements. This paper discusses the effects of a simple modification, consisting of drilled horizontal holes through the elastomeric layers of the bearings, on the lateral response of FREIs. A desirable hardening response and a stability range up to 100% of shear strain has been obtained on modified bearings. This result has been confirmed by experimental tests and finite element analyses. Findings of this work show how the proposed modification allows (i) to reduce the horizontal stiffness of FREIs, (ii) to increase the stable range of lateral deformations of the devices and (iii) to obtain a desired hardening behavior under large horizontal displacements without instability.

Human discrimination and modeling of high-frequency complex tones shed light on the neural codes for pitch.

Accurate pitch perception of harmonic complex tones is widely believed to rely on temporal fine structure information conveyed by the precise phase-locked responses of auditory-nerve fibers. However, accurate pitch perception remains possible even when spectrally resolved harmonics are presented at frequencies beyond the putative limits of neural phase locking, and it is unclear whether residual temporal information, or a coarser rate-place code, underlies this ability. We addressed this question by measuring human pitch discrimination at low and high frequencies for harmonic complex tones, presented either in isolation or in the presence of concurrent complex-tone maskers. We found that concurrent complex-tone maskers impaired performance at both low and high frequencies, although the impairment introduced by adding maskers at high frequencies relative to low frequencies differed between the tested masker types. We then combined simulated auditory-nerve responses to our stimuli with ideal-observer analysis to quantify the extent to which performance was limited by peripheral factors. We found that the worsening of both frequency discrimination and F0 discrimination at high frequencies could be well accounted for (in relative terms) by optimal decoding of all available information at the level of the auditory nerve. A Python package is provided to reproduce these results, and to simulate responses to acoustic stimuli from the three previously published models of the human auditory nerve used in our analyses.

Properties of Fiber Bragg Grating in CYTOP Fiber Response to Temperature, Humidity, and Strain Using Factorial Design.

The characteristics of fiber Bragg grating (FBG) in cyclic transparent fluoropolymer (CYTOP) optical fiber have attracted more and more attention in recent years. However, different results of the FBG response to environmental parameters are reported. This work presents a three-variable two-level factorial experimental method to investigate the FBG response to temperature, humidity, and strain in CYTOP fiber. Two uniform FBGs are inscribed separately in CYTOP fiber with and without over-clad. With only eight measuring points, the interactions among three variable parameters are computed and the parameter sensitivities and cross-sensitivities are estimated. Similar temperature and strain sensitivities were found for both gratings, whereas significant cross-sensitivity between humidity and temperature was present only in FBG inscribed in CYTOP fiber with over-clad.

Loss of central mineralocorticoid or glucocorticoid receptors impacts auditory nerve processing in the cochlea

SummaryThe key auditory signature that may associate peripheral hearing with central auditory cognitive defects remains elusive. Suggesting the involvement of stress receptors, we here deleted the mineralocorticoid and glucocorticoid receptors (MR and GR) using a CaMKIIα-based tamoxifen-inducible CreERT2/loxP approach to generate mice with single or double deletion of central but not cochlear MR and GR. Hearing thresholds of MRGRCaMKIIαCreERT2 conditional knockouts (cKO) were unchanged, whereas auditory nerve fiber (ANF) responses were larger and faster and auditory steady state responses were improved. Subsequent analysis of single MR or GR cKO revealed discrete roles for both, central MR and GR on cochlear functions. Limbic MR deletion reduced inner hair cell (IHC) ribbon numbers and ANF responses. In contrast, GR deletion shortened the latency and improved the synchronization to amplitude-modulated tones without affecting IHC ribbon numbers. These findings imply that stress hormone-dependent functions of central MR/GR contribute to “precognitive” sound processing in the cochlea.

On the response of flax fiber reinforced composites under salt-fog/dry conditions: Reversible and irreversible performances degradation

Despite their scarce resistance to humid or wet conditions, natural fiber reinforced composites (NFRCs) seem to be able to partially recover their performances under discontinuous exposition to marine environment. To investigate this peculiarity, flax fiber reinforced composite was at first subjected to salt-fog spray condition at 35 °C for 15 and 30 days, respectively, and then stored in ‘‘dry” condition (i.e., 50% R.H. and 22 °C) between 0 and 21 days. The performances evolution was evaluated through flexural tests, water uptake and contact angle measurements. Moreover, the morphology of fractured mechanical samples was examined by using 3D optical microscope and scanning electron microscope (SEM). Flax fiber reinforced composite experienced phenomena of both reversible and irreversible degradation during the wet phase thus evidencing a relevant mechanical recovery thanks to the drying. Quite interestingly, the laminate showed an almost complete recovery of the flexural strength, meaning that this property is more strictly related to mainly reversible aging phenomena whereas the greater stiffness loss is more probably due to irreversible ones.

Comprehensive Characterization of PVDF Nanofibers at Macro- and Nanolevel.

This study is focused on the characterization and investigation of polyvinylidene fluoride (PVDF) nanofibers from the point of view of macro- and nanometer level. The fibers were produced using electrostatic spinning process in air. Two types of fibers were produced since the collector speed (300 rpm and 2000 rpm) differed as the only one processing parameter. Differences in fiber’s properties were studied by scanning electron microscopy (SEM) with cross-sections observation utilizing focused ion beam (FIB). The phase composition was determined by Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The crystallinity was determined by differential scanning calorimetry (DSC), and chemical analysis of fiber’s surfaces and bonding states were studied using X-ray photoelectron spectroscopy (XPS). Other methods, such as atomic force microscopy (AFM) and piezoelectric force microscopy (PFM), were employed to describe morphology and piezoelectric response of single fiber, respectively. Moreover, the wetting behavior (hydrophobicity or hydrophilicity) was also studied. It was found that collector speed significantly affects fibers alignment and wettability (directionally ordered fibers produced at 2000 rpm almost super-hydrophobic in comparison with disordered fibers spun at 300 rpm with hydrophilic behavior) as properties at macrolevel. However, it was confirmed that these differences at the macrolevel are closely connected and originate from nanolevel attributes. The study of single individual fibers revealed some protrusions on the fiber’s surface, and fibers spun at 300 rpm had a core-shell design, while fibers spun at 2000 rpm were hollow.

Multiscale mechanobiology: Coupling models of adhesion kinetics and nonlinear tissue mechanics

The mechanical behavior of tissues at the macroscale is tightly coupled to cellular activity at the microscale. Dermal wound healing is a prominent example of a complex system in which multiscale mechanics regulate restoration of tissue form and function. In cutaneous wound healing, a fibrin matrix is populated by fibroblasts migrating in from a surrounding tissue made mostly out of collagen. Fibroblasts both respond to mechanical cues, such as fiber alignment and stiffness, as well as exert active stresses needed for wound closure.Here, we develop a multiscale model with a two-way coupling between a microscale cell adhesion model and a macroscale tissue mechanics model. Starting from the well-known model of adhesion kinetics proposed by Bell, we extend the formulation to account for nonlinear mechanics of fibrin and collagen and show how this nonlinear response naturally captures stretch-driven mechanosensing. We then embed the new nonlinear adhesion model into a custom finite element implementation of tissue mechanical equilibrium. Strains and stresses at the tissue level are coupled with the solution of the microscale adhesion model at each integration point of the finite element mesh. In addition, solution of the adhesion model is coupled with the active contractile stress of the cell population. The multiscale model successfully captures the mechanical response of biopolymer fibers and gels, contractile stresses generated by fibroblasts, and stress-strain contours observed during wound healing. We anticipate that this framework will not only increase our understanding of how mechanical cues guide cellular behavior in cutaneous wound healing, but will also be helpful in the study of mechanobiology, growth, and remodeling in other tissues.

Interventional effect of asiaticosdide on rats exposed to silica dust

Objective: To investigate the effect of asiaticoside for fibrosis in lung tissues of rats exposed to silica and to explore its possible mechanism. Methods: 144 SD male rats were randomly divided into control group, model group, positive drug control group, asiaticoside high-dose group, medium-dose group and low-dose group, each group included 24 rats. Rats in the control group were perfused with 1.0 ml of normal saline, and the other groups were given 1.0 ml 50 mg/ml SiO(2) suspension. Gavage of herbal was given from the next day after model establishment, once a day. Rats in the positive drug control group were administration with 30 mg/kg tetrandrine and rats in the low-dose group, medium-dose group and high-dose group were given 20 mg/kg, 40 mg/kg and 60 mg/kg asiaticoside for fibrosis respectively. Rats in the control group and the model group were given 0.9% normal saline. The rats were sacrificed in on the 14th, 28th and 56th day after intragastric administration and collect the lung tissues to detect the content of hydroxyproline, TGF-β(1) and IL-18, observe the pathological changes of the lung tissues by HE and Masson staining and determine the expressions of Col-I, a-SMA, TGF-β in lung tissues by Western Blot. Results: On the 14th day, 28th day and 56th day after model establishment, the lung tissues of rats in the model group showed obvious inflammatory response and accumulation of collagen fibers, and the degree of inflammation and fibrosis increased with time. The intervention of asiaticoside could effectively inhibit the pathological changes of lung tissues. The contents of hydroxyproline, IL-18 and TGF-β1 in lung tissues of model group were higher than those in the control group (P<0.05) , while the level of hydroxyproline, IL-18 and TGF-β1 in asiaticoside groups were significantly decreased, and the difference was statistically signicant (P<0.05) . Compared with the control group, the expression levels of Col-I, TGF-β1and α-SMA in lung tissue of model group were increased (P<0.05) , while the expression level of Col-I, TGF-β1 and α-SMA were decreased after the intervention of asiaticoside, and the difference was statistically signicant (P<0.05) . Conclusion: Asiaticoside can inhibit the increase of Col-I, TGF-β1 and α-SMA content in the SiO(2)-induced lung tissues of rats, reduce the release of TGF-β1 and IL-18 inflammatory factors in lung tissue, and then inhibit the synthesis and deposition of extracellular matrix in rat lung tissue, and improve silicosis fibrosis.

In-plane Shear Response of a Flax Fiber-epoxy Resin Composite Subjected to Repeated Loading and Creep-recovery Cycles

The present paper is aimed at studying the in-plane shear response of a flax fiber - epoxy resin composite laminate. Rectangular specimens, with �45� laminate orientation with respect to loading direction were used for the experimental procedure. Tensile testing up to failure allowed to extract the shear strain-shear stress curve, which have shown a linear domain, up to approximately 25 MPa, where a shear modulus was calculated, of 1.67 GPa and a Poisson ratio of 0.7, value which is typical for off axis laminates. Strain measurement during these tests, using Digital Image Correlation, have shown that, at high stress levels, concentrators occur in the specimen in the region of failure. Repeated loading tests have shown that the material stiffens approximately 9% when increasing loading speed, leading to conclude that a viscoelastic component of the deformation is present during loading. Repeated creep-recovery tests showed that, for longer periods of time, viscoplastic deformations appear as well, with an exponential evolution with respect to the creep duration.

Исследование радиационного отклика оптического волокна при воздействии импульсного ионизирующего излучения

We have studied the radiation response of a single-mode optical fiber under the influence of pulsed photon and gamma-neutron radiation. The recovery time of the characteristics of the same optical fiber for one dose per pulse can vary within a wide range from a few milliseconds to several seconds, depending on various influencing factors. It is for the first time that we have experimentally recorded an increase of radiation-induced attenuation (RIA) of an optical fiber in the short-wavelength region after exposure to a pulsed neutron flux, simultaneously with RIA decrease in the long-wavelength region after the end of exposure and a subsequent RIA decrease in the entire studied wavelength range. This may mean a reversible rearrangement of the glass structure of the optical fiber. The RIA curves of the optical fibers under the influence of pulsed ionizing radiation are analyzed using the approaches of chemical kinetics. It has been established that the reaction order of the relaxation processes of short-lived radiation-induced color centers (RTCs) is fractional, which indicates a complex, possibly multi-stage process. After a few microseconds after exposure, all relaxation processes are in the diffusion region. The paper is the first to show that the characteristic RTCs relaxation time is directly related not only to temperature but also to the level of the stress-strain state of the optical fiber, and for an optical fiber with a pure-silica core, it is additionally related to the input optical power.

An analytical studies on static and fatigue response of steel fibre and re-cycled aggregate integrated high strength concrete beam

Many researchers have examined the reaction of structural elements made of High Strength Concrete (HSC). HSC performance and efficiency under static and impact loading have been improved in the recent years. The objective of this research paper is to analyse the HSC beams incorporated with 30% of Re-Cycled Aggregate (RCA) with partial replacement of coarse aggregate and adding 1% of steel fibres beneath static loading condition and the behaviour is identified. The HSC beam is evaluated with static load condition analytically. A Finite Element Modelling (FEM) with the well-known finite element ANSYS program is proposed for the analyse of HSC beam. The static load will be implemented and the effects will be addressed. The fatigue load is used for the HSC beam efficiency estimation in the model. The S-N Curve for continuous loading of amplitude is defined in fatigue analysis. The ANSYS program was used to investigate the ultimate load and deformation for HSC beams with steel fibres and recycled aggregates under static loading as well as the evolution of the S-N curve during fatigue loading.

Pseudo-ductility under tensile and compressive loading in ±45º laminates

This work focuses on analyzing the uniaxial response of carbon fiber reinforced polymer matrix laminates with the configurations [&plusmn;45]2S under tension and [&plusmn;45]4S under compression. These present non-linear stress-strain evolutions that allow them to withstand large deformations before losing their load-carrying capacity. Both responses are characterized by a first linear stage, followed by a plateau in which the strain grows without increasing the stress level, and finally by a re-stiffening phase. But there are quantitative differences that lead to different failure patterns, which are explained with the help of the state of stress in the plane of maximum shear stress. For a better understanding of the process, tensile load-unload-reload tests are performed to verify if the energy recovered in each cycle could be related to the loss of the apparent stiffness. During the first two stages of the mechanical response, the laminate suffers a progressive damage with a reduction in stiffness related to the dissipated energy, but this pattern is not repeated in the last stage of strain hardening. Based on the experience of other authors, it is assumed that the re-stiffening stage follows a different pattern due to possible microstructural changes in the matrix during the plateau. These are promoted by a narrowing process under tensile loads and a local widening of the test zone under compression. The dimensional changes perpendicular to the load direction are observed thanks to the strain fields obtained by Digital Image Correlation.

Nonlinear response under several multiaxial loading states in fibre reinforced polymer laminates

The present work includes a summary of the doctoral thesis entitled &quot;Complexity of the structural response of fibre reinforced polymer matrix composites&quot;. This PhD thesis focused on analyzing the nonlinear mechanical response of a set of stacking sequences, with main interest in angle-ply laminates, to detail the stress-strain behaviour under a range of loading states: uniaxial tension/compression, loading-unloading-reloading tensile tests, three-point bending and plane stress states. The aim is to delve into the mechanisms of coupling and damage and their influence on the mechanical behaviour, in some cases highly nonlinear, aiming to achieve that the material withstands large strains with the consequent delay of the final failure and the increase in energy absorption capacity. Thanks to the characterization through standard testing, it is possible to calibrate material models based on progressive damage, providing two different numerical approaches which are tested against the different experimentally generated states of plane stress. In addition, it is worth mentioning the biaxial tests on cruciform specimens under different loading ratios, which provide experimental data closer to the actual response of composite structures in service. These tests, due to their greater complexity and lack of standardization, are analyzed in detail by applying numerical simulations and analytical models that ensure the validity of the results, highlighting the possible instabilities generated in the presence of compressive loads.