Uniaxial Cyclic Loading Research Articles

Investigation of Fatigue Mechanics and Crack Evolution Characteristics of Jointed Specimens Under Cyclic Uniaxial Compression

ABSTRACTNonpersistent joints are prevalent in engineering rock masses and are sensitive to cyclic loads induced by geological movements and engineering disturbances. Therefore, studying the fatigue mechanisms of rock masses with nonpersistent joints under cyclic compressive loads is crucial for ensuring the rational design and long‐term stability of rock engineering structures. Based on laboratory experiments, this study employed the discrete element method to create specimens with different nonpersistent joints, and uniaxial compressive cyclic loading tests were conducted on these specimens with different maximum cyclic stress levels. The results show that the joint inclination significantly affects the characteristics of jointed rock, such as deformation modulus, irreversible strain, energy evolution, and crack characteristics. Increasing the maximum stress in the stress path results in a rapid release of hysteretic energy in the jointed regions of the rock, which leads to an exponential decrease in fatigue life while an increase in initial irreversible strain, final irreversible strain, and hysteretic energy density. Additionally, the shear fracture zones on both sides of the model expand, and the propagation and merging of cracks between joints become more extensive and complex. The results are significant for studying rock fatigue instability and structure engineering design.

Enhancing energy dissipation in mortar utilizing recycled brick fine aggregate impregnated with polymer emulsion under uniaxial cyclic load

Optimizing the damping properties of materials can enhance the energy dissipation capacity of structures and mitigate the negative effects of dynamic loads on building components. This study investigated the effects of the polymer emulsion-impregnated recycled brick fine aggregate (PRBFA) replacement rate, emulsion-impregnation treatment method, and emulsion solid content on the dynamic damping properties of PRBFA-prepared mortar (PBM). Combined with microscopic tests, the enhanced damping mechanism of PBM was discussed. The results show that under the same stress amplitude, the equivalent damping ratio and loss modulus of PBM increase with the PRBFA replacement rate and emulsion solid content. The drying treatment of PRBFA demonstrates superior damping characteristics of PBM, with the equivalent damping ratio and loss modulus increased by 84.9%–129.4 % and 71.0%–117.2 %, respectively, compared to those of PBM with undried PRBFA. The damping enhancement of PBM is attributed to the weak interface between the aggregate and cement matrix, which facilitates slippage and friction. The damping layer formed between the high viscoelastic emulsion and the aggregate, or between the emulsion and the cement matrix, is conducive to energy dissipation. The optimal PRBFA replacement rate for balancing the mechanical and damping properties of PBM is between 38% and 60 %.

Mechanical behaviour and instability mechanism of sandstones with impact tendency under different loading paths

ABSTRACT To reveal the instability and failure mechanism of pillars with impact tendency, the Brazilian test, uniaxial compressive test, cyclic loading and unloading (CLU) tests were performed on sandstones which had impact tendency. The stress drop phenomenon was obvious in the fracture stage during the Brazilian test. The main tensile crack with penetration type appeared. Under the CLU condition, the CLU had a significant effect in enhancing the mechanical character of rocks. Under the combined loading, the character stress of rocks tested with the CLU was greater than the uniaxial loading. Moreover, the greater the first cyclic threshold, the greater the character stress of rocks. Under the uniaxial loading, the failed samples showed tensile fractures. The damage location of the samples was closely related to the Poisson effect and the ending face effect. With the electron microscope which had the same magnification, the crack deterioration degree of samples under the uniaxial loading was greater than the CLU condition. Moreover, with the first cycle threshold increasing, the surface roughness of rocks gradually decreased. The quantity of secondary micro cracks gradually decreased. The propagation and penetration phenomenon gradually disappeared. The micro structure and loading properties of rocks were affected by the bonding force and structural characters between the internal structure and matrix. Based on the micro-seismic signal of the damaging threshold, the seismic source damage location can be located. Moreover, the pillar-typed burst area can be forewarned. This research benefits predicting the pillar-typed burst disaster.

Mechanical Properties of Latex-Modified Cement Stone under Uniaxial and Triaxial Cyclic Loading.

During the cyclic injection and extraction process in underground storage wellbores, the cement sheath undergoes loading and unloading stress cycles. In this study, we investigated the mechanical properties of latex-modified cement stone (LMCS), widely used in oil and gas wells, through uniaxial and triaxial cyclic loading and unloading tests. The aim of the study was to determine the effect of various loading conditions on the compressive strength and stress-strain behavior of LMCS. The results show that the stress-strain curve of LMCS exhibits a hysteresis loop phenomenon, with the loop intervals decreasing throughout the entire cyclic loading and unloading process. As the number of cycles increases, the cumulative plastic strain of the LMCS increases approximately linearly. Under uniaxial cyclic loading and unloading conditions, the elastic modulus tends to stabilize. However, under triaxial conditions, the elastic modulus increases continuously as the number of cycles increases. This result provides data for engineering predictions. Furthermore, a comparison of the uniaxial and triaxial cyclic loading and unloading of LMCS shows that its cumulative plastic strain develops rapidly under uniaxial conditions, while the elastic modulus is larger under triaxial conditions. These findings provide a valuable reference for constructing underground storage wellbores.

Precursors of rock failure under cyclic loading and unloading: From the perspective of energy and acoustics

The precursor characteristics of rock failure under cyclic loading and unloading are crucial to the prevention of underground engineering disasters. Taking sandstone as an example, this work conducted rock failure experiments under uniaxial cyclic loading and unloading combined with active wave velocity and passive acoustic emission (AE). The damage evolution process of rock was analyzed from the perspectives of energy, AE, and wave velocity. The results show that as the cyclic load stress level increases, the rigidity of the rock continuously increases, the proportion of elastic energy may reach a peak, and there will be an extreme time difference between the wave velocity and stress. The occurrence of the peak point of elastic energy proportion is a sufficient and unnecessary condition for the precursor characteristics of rock failure. The appearance of numerous AE events with high amplitude and high count is an effective precursor characteristic of rock failure. The stress continues to increase while wave velocity decreases is a key precursor characteristic of rock failure. There is a clear linear relationship between wave velocity drop and dissipated energy, it implies that both the which can quantitatively evaluate the rock damage under cyclic loading and unloading. The variation of wave velocity exhibits obvious anisotropic characteristics. This paper is not only a beneficial supplement to the theoretical system of rock failure precursors, but also provides new ideas and methods for rock stability monitoring and failure disaster early warning in underground engineering.

Study on fatigue characteristics of red sandstone under extremely high stress in the hydro-chemical environment

To study the failure of red sandstone under extremely high stress during the service life of tunnels, an in-depth study was conducted on the mechanical properties of red sandstone under uniaxial loading and cyclic loading and unloading processes at different pH values using the AG-250kNIS electronic precision material testing machine and MTS815 mechanical testing machine. The results show that as the acidity and alkalinity increase, the peak stress under uniaxial loading decreases and the axial strain increases,The peak stress at failure is 9.40, 12.37, 7.18, and 5.36 MPa, respectively, accounting for 74.19%, 68.91%, 40.38%, and 36.21% of the uniaxial compressive strength; The number of cycles significantly decreases during cyclic loading and unloading fatigue failure, and the stress required for sandstone failure gradually decreases. The peak strength and elastic modulus of sandstone show a decreasing trend, indicating that the hydrochemical environment plays an accelerating role in rock degradation. During the cyclic loading and unloading process of sandstone, there is a continuous increase in dissipated energy and finally a sudden increase, the Ud/U and Ue/U ratios at the peak point of sandstone in the natural state are 0.399 and 0.601, respectively, while the overall elastic energy shows an increasing trend; and a damage evolution model was established based on dissipative energy, which can better describe the degradation process of red sandstone.

Investigating infrared Radiation, Energy, and fracture evolution features of dry and wet coal under cyclic loading

The continuous mining activities at the working face cause periodic disturbances to the surrounding coal rock mass. Investigating the response characteristics of surface infrared radiation temperature, energy evolution features, and fracture development patterns in coal rock under cyclic loading and unloading is crucial for enhancing our understanding of the mechanisms of damage, degradation, and instability in rocks associated with mining operations. In this research work, we conducted infrared radiation observation experiments on both dry and wet coal samples subjected to uniaxial cyclic loading and unloading. Furthermore, we carried out a thorough analysis of the resulting temperature variations, energy changes, and fracture evolution patterns. It was found that the average infrared radiation temperature (AIRT) generally increases during the loading phase and decreases during the unloading phase, with the variance of successive minus infrared image temperature (VSMIT) exhibiting a sharp change just prior to failure. Energy analysis indicates that dissipated energy during the pore compaction and elastic deformation stages is minimal, while in the plastic deformation stage, the proportion of dissipated energy to total energy increases, displaying a “concave” upward trend. Additionally, fitting results show that the AIRT follows a single exponential decay relationship with dissipated energy, with wet coal exhibiting a greater decay coefficient, highlighting that moisture accelerates the rate of temperature decline. The Particle Flow Code (PFC) simulation results further demonstrate that the number of cracks in dry coal samples significantly exceeds that in wet coal samples, showing a single exponential relationship between the number of fractures and dissipated energy, which indicates that the development of fractures in dry coal rock occurs at a faster rate with increasing dissipated energy compared to wet coal rock.

On the cyclic elastoplastic shakedown behavior of an auxetic metamaterial: An experimental, numerical, and analytical study

This article presents the first experimental, numerical, and analytical study of the elastoplastic shakedown response of an auxetic metamaterial structure that elucidates interactions between auxeticity and maximum shakedown loading capacity. The study aims to determine the safe elastoplastic shakedown limit of perforated auxetic aluminum sheet structures (AA5083-TO) with fixed void fraction (16.4%) under ambient cyclic asymmetric uniaxial loading conditions. The motivation is that shakedown-based designs can be used to expand the feasible design space under cyclic loading conditions compared to conventional yield-limited designs. Finite element analyses with calibrated hardening models are used to develop Bree load-interaction diagrams that are experimentally validated. It is found that shakedown occurs at stress levels up to almost four times the elastic limit of the structure for a fixed allowable equivalent strain level near three percent. This shakedown multiplier is also sensitive to the extent of auxeticity in the structure and a parametric study and analytical model are used to identify underlying mechanisms and a potential maximum condition.

Study on the mesoscopic mechanical behavior and damage constitutive model of micro-steel fiber reinforced recycled aggregate concrete

This study employs in-situ 4D CT experimental techniques to investigate the mesostructured changes and mechanical behavior of micro steel fiber-reinforced recycled aggregate concrete (MSF-RAC) under uniaxial compression and cyclic loading conditions. The research aims to address the scientific problem of limited understanding of how micro steel fibers affect the mesoscopic mechanical behavior and structural damage characteristics of recycled aggregate concrete. High-resolution CT scanning technology was utilized for real-time observation of crack initiation and propagation, revealing the micro-mechanisms by which micro steel fibers enhance RAC. The study found that incorporating micro-steel fibers significantly improves the density of the interfacial transition zone (ITZ), inhibits crack development, and enhances the mechanical properties of the concrete. Based on these observations, an improved stiffness degradation damage constitutive model was proposed, which comprehensively considers the distribution orientation of micro steel fibers and ITZ characteristics. The model effectively predicts the stress-strain relationship of MSF-RAC under various conditions, demonstrating high accuracy and practicality. These findings provide important theoretical support and experimental evidence for the optimal design of RAC, showcasing significant engineering application value by promoting the sustainable use of recycled materials in construction.

Damage evolution, acoustic emission and electromagnetic radiation of rock under uniaxial cyclic loading

Uniaxial cyclic loading compression experiments are conducted with synchronous monitoring of acoustic emission (AE) and electromagnetic radiation (EMR). The AE and EMR characteristics of rocks during cyclic loading are analyzed. Subsequently, the Kaiser and Felicity effects of AE and EMR are disclosed. Moreover, the b-value and fractal dimension are calculated to explore the cracking mechanism of rock materials. These results show that the AE and EMR are active during the 1st and 2nd loading cycles, and sparse during the 3rd and 4th loading cycles where the AE and EMR are only generated when the stress exceeds the previous peak stress due to the Kaiser effect. In the 5th loading cycle, AE and EMR accelerate and peak at rock failure. The variation of EMR-based FR is consistent with that for AE under cyclic loading. Hence, the FR associated with EMR is also well correlated with stress memory. The AE and EMR-based FR is greater than 1 in the 2nd-4th loading cycles, and less than 1 in the 5th cycle, indicating that FR can be used to reflect the damage evolution of rocks. The b-value and fractal dimension increase in the 1st-4th loading cycles, and turn to decrease in the 5th loading cycle. This pattern serves as a precursor to identify the rock failure.

Laboratory investigation on static and dynamic properties, durability, and microscopic structure of Nano-SiO2 and polypropylene fiber cemented soil under coupled seawater corrosion and cyclic loading

Cemented soils in coastal harbors are susceptible to adverse factors such as seawater corrosion and cyclic dynamic loading, which may consequently reduce their stability and durability. In recent years, Nano-SiO2(NS) has been widely used to enhance the mechanical properties of cemented soil. However, this enhancement may potentially lead to a reduction in ductility. Conversely, polypropylene fibers (PP) have attracted widespread attention for their potential to enhance the ductility of cemented soils, but their ability to improve the strength of cemented soils is limited. To address these issues, this study focused on utilizing five different nano-dosages combined with four different fiber dosages to enhance cemented soils. These enhanced soils were then subjected to curing periods of 7, 28, and 60 days in seawater environments. The study employed various tests including unconfined compressive strength tests (UCS), uniaxial cyclic loading tests, scanning electron microscopy tests (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) to investigate the potential impacts of these additives on durability, strength, corrosion resistance, and microstructure evolution. The results of the study indicate that seawater corrosion and cyclic loading contribute to a reduction in the stability of cemented soils. However, the addition of NS and PP effectively enhances the compressive strength and durability of these soils. The optimal combination ratio is achieved when the dosages of NS and PP are 3.6 % and 0.8 %, respectively. In this case, the growth rate of unconfined compressive strength of cemented soils surpasses the sum of each individual dosage, increasing by 137.7 %, 245.6 %, and 235.3 % after 7, 28, and 60 days of curing, respectively. Furthermore, the growth rate of PP on the compressive strength of cemented soils remains largely unaffected by seawater corrosion. The optimal composite dosage of cemented soils effectively mitigates the increase in porosity caused by seawater corrosion. C-S-H enhances the mechanical interlocking between hydration products and PP by encapsulating PP, reducing energy transfer losses in cemented soils, and increasing their dynamic modulus. The volcanic ash reaction and nucleation effect of NS further enhance this effect, and their combined use significantly improves the seawater corrosion resistance of cemented soils.

Thermal conductivity loss in WC-Co hard metal due to high-temperature cyclic loading damage as a function of microstructure and temperature

Many structures made of WC-Co hard metal are subject to thermo-mechanical loading and have to conduct heat in order to function properly in industrial application. The current work provides results on a significant drop in thermal conductivity of WC-Co hard metals as a function of material volume damage that accumulates during cyclic high-temperature loading of the materials depending on material microstructure. Average WC grain size and Co binder metal content of the investigated grades ranged from submicron to medium and from 10 to 12 wt%, respectively. The hard metals were subjected to uniaxial cyclic loading in a vacuum for different numbers of load cycles at 700 °C and 800 °C. Damage features accumulated in the material volume were documented by means of scanning electron microscopy. Thermal conductivity properties of virgin and damaged materials were determined via laser flash analysis. The results indicated a significant decrease depending on the materials' microstructure, i.e. the defects' predominant location within the microstructure. The damage features that occurred mainly between WC grains in the coarser-grained grade led to larger drops in thermal conductivity with rising temperature compared to damage features that occurred within the Co binder metal in the finer-grained grade. The presented results are of high relevance to the thermo-mechanical load situation of e.g. milling tools since the heat conduction away from their cutting edges is hindered by the documented effect and deemed to lead to a self-acceleration of the damage accumulation.

Heat exchange and damage of carbon black‐filled styrene‐butadiene rubber under uniaxial cyclic loading

AbstractIn this paper, we present an original experimental approach combining infrared thermography, analysis of voiding, and swelling tests to investigate damage mechanisms in carbon black (CB)‐filled styrene‐butadiene rubber (SBR). Heat exchange and voiding under uniaxial cyclic loading have been observed. A mechanical and electrical percolating filler network was identified by atomic force microscopy and electrical conductivity for the SBR with highest content of fillers (60 phr). SBR materials with a non percolating filler network show a reversible thermal energy dissipation during a series of cyclic loading, concomitant with reversible voiding mechanisms, through the successive formation and closing of voids. The SBR with the percolating network undergoes, during the series of cyclic loading, a high dissipation of energy under the form of heat, concomitantly with irreversible voiding mechanisms. Such mechanisms are shown to be due primarily to (i) the alteration of the filler network and/or filler/rubber interface and to a lower extent to (ii) the rubber matrix alteration (chains scission and/or crosslink breakage) as demonstrated by ex‐situ swelling.

Mechanical behaviors and progressive fracture processes of dry basalt after Martian cryogenic freeze-thaw cycles

The steep Martian terrain features numerous notches and alcoves that could potentially be adapted as temporary shelters. By sealing their entrances and modifying the interior space, these alcoves can be transformed into habitable structures. Given their prolonged exposure to Martian temperature fluctuations, it is crucial to understand the mechanical properties of alcove rocks to design appropriate shelter parameters. This study investigates the mechanical behavior of basalt specimens subjected to Martian cryogenic freeze-thaw (F-T) cycles (−143∼35 °C) and subsequent uniaxial cyclic loading tests. The test results indicate that the longitudinal wave velocity, peak stress, and elastic modulus of basalt specimens degrade to varying degrees with an increasing number of F-T cycles. At higher stress levels, the ratio of dissipated energy density to elastic energy density in basalt specimens subjected to different F-T treatments converges to approximately 0.25. During the uniaxial cyclic loading tests, both cumulative acoustic emission (AE) counts and average maximum principal strains of the specimens increase stepwise. For specimens after F-T treatment, the spectral-domain characteristics can be classified into three frequency bands, with the middle and high frequencies predominating. The application of the Gaussian Mixture Model (GMM) clustering algorithm enhances the analysis of AE results, facilitating the identification of tensile and shear cracks. As the number of F-T cycles increases, the percentage of shear cracks in basalt specimens decreases from 76.5% (0 cycle) to 53.5% (7 cycles).

Experimental Investigation on Freeze–Thaw Damage Mechanism of Xiyu Conglomerate Under Uniaxial Cyclic Loading

Experimental Investigation on Freeze–Thaw Damage Mechanism of Xiyu Conglomerate Under Uniaxial Cyclic Loading

Mechanical properties and acoustic emission characteristics of soft rock with different water contents under dynamic disturbance

Uniaxial compression tests and cyclic loading acoustic emission tests were conducted on 20%, 40%, 60%, 80%, dry and saturated muddy sandstone by using a creep impact loading system to investigate the mechanical properties and acoustic emission characteristics of soft rocks with different water contents under dynamic disturbance. The mechanical properties and acoustic emission characteristics of muddy sandstones at different water contents were analysed. Results of experimental studies show that water is a key factor in the mechanical properties of rocks, softening them, increasing their porosity, reducing their brittleness and increasing their plasticity. Under uniaxial compression, the macroscopic damage characteristics of the muddy sandstone change from mono-bevel shear damage and ‘X’ type conjugate bevel shear damage to a roadway bottom-drum type damage as the water content increases. Dynamic perturbation has a strengthening effect on the mechanical properties of samples with 60% and less water content, and a weakening effect on samples with 80% and more water content, but the weakening effect is not obvious. Macroscopic damage characteristics of dry samples remain unchanged, water samples from shear damage and tensile–shear composite damage gradually transformed into cleavage damage, until saturation transformation monoclinic shear damage. The evolution of acoustic emission energy and event number is mainly divided into four stages: loading stage (I), dynamic loading stage (II), yield failure stage (III), and post-peak stage (IV), the acoustic emission characteristics of the stages were different for different water contents. The characteristic value of acoustic emission key point frequency gradually decreases, and the damage degree of the specimen increases, corresponding to low water content—high main frequency—low damage and high water content—low main frequency—high damage.

Mechanistic model for hydrogen accelerated fatigue crack growth in a low carbon steel

Fracture by hydrogen accelerated fatigue crack growth is a severe type of environmental failure. Although fatigue crack growth has been the subject of intense investigation over several decades, a complete mechanistic and predictive model is still lacking. Such a crack growth model is even more rare in the case of hydrogen in view of the lack also of constitutive models for material deformation under cycling loading that account for the hydrogen effect. In this study, we present a model for fatigue crack propagation induced by alternating crack tip plastic blunting and re-sharpening, which in the presence of hydrogen can be accelerated by hydrogen enhanced dislocation motion and generation. The Chaboche constitutive model, which is a nonlinear kinematic hardening model capable of capturing many features of material behavior under cyclic loading, is used for the calculation of the stress and strain fields at the propagating crack tip. The Chaboche model is calibrated using a sequence of experimental data from uniaxial strain-controlled cyclic loading tests and uniaxial stress-controlled ratcheting tests with a low carbon steel, JIS SM490YB, in the absence and presence of hydrogen. The numerical simulation results indicate that the proposed crack propagation model can predict Paris law behavior and can successfully demonstrate acceleration of fatigue crack growth in the presence of hydrogen. Significantly, the profiles of the steady-state opening stress and strain ahead of the fatigue crack tip in a compact tension (C(T)) specimen were found to have sections over which they vary as ln(1/r) with distance r from the crack tip, consistent with the crack-tip strain field for a non-stationary crack.

Role of the microstructure and the residual strains on the mechanical properties of cast tungsten carbide produced by different methods

Cast tungsten carbide (CTC) is a biphasic, pearlitic-like structure composed of WC lamellae in a matrix of W2C. Besides excellent flowability, spherical CTC powders exhibit superior hardness and wear resistance. Nevertheless, the available literature generally fails to explain the physical mechanisms behind such a phenomenon. In the present work, the microstructure and the mechanical properties of the novel centrifugally-atomized spherical CTC have been extensively investigated. This material exhibited an extremely fine microstructure, with WC lamellae of 27–29 nm in thickness and bulk lattice strains of 1.0–1.4 %, resulting in a microindentation hardness of 31.4 ± 1.6 GPa. The results of this study clearly show that centrifugally-atomized CTC is mechanically superior to both spheroidized CTC and conventional cast-and-crushed CTC. In addition, the effect of a series of heat treatments on the bulk fracture toughness and the fatigue life of entire CTC particles was also investigated. The reduction of residual stresses in the bulk of particles upon annealing dramatically increased the indentation fracture toughness, whereas the bulk microindentation hardness remained essentially unaffected. Regarding the fatigue life of entire particles under uniaxial cyclic compressive loading, local phase transformation phenomena at the surface of the particles upon heat treatment were concluded to play the most critical role. Indeed, the cumulative fatigue damage was minimized in surface-carburized CTC powders, where compressive stresses were induced at the outermost surface.

Design strategy of porous elastomer substrate and encapsulation for inorganic stretchable electronics

ABSTRACT The emergence of stretchable electronic technology has led to the development of many industries and facilitated many unprecedented applications, owing to its ability to bear various deformations. However, conventional solid elastomer substrates and encapsulation can severely restrict the free motion and deformation of patterned interconnects, leading to potential mechanical failures and electrical breakdowns. To address this issue, we propose a design strategy of porous elastomer substrate and encapsulation to improve the stretchability of serpentine interconnects in island-bridge structures. The serpentine interconnects are fully bonded to the elastomer substrate, while segments above circular pores remain suspended, allowing for free deformation and a substantial improvement in elastic stretchability compared to the solid substrates. The pores ensure unimpeded interconnect deformations, and moderate porosity provides support while maintaining the initial planar state. Compared to conventional solid configurations, finite element analysis (FEA) demonstrates a substantial enhancement of elastic stretchability (e.g. ≈9 times without encapsulation and ≈ 7 times with encapsulation). Uniaxial cyclic loading fatigue experiments validate the enhanced elastic stretchability, indicating the mechanical stability of the porous design. With its intrinsic advantages in permeability, the proposed strategy has the potential to offer insightful inspiration and novel concepts for advancing the field of stretchable inorganic electronics.

Understanding seawater-induced fatigue changes in glass/epoxy laminates: A SEM, EDS, and FTIR study

Composite polymeric materials have exhibited significant advantages when operating in hostile conditions such as the marine environment. However, there is a lack of information concerning three-dimensional variations induced by prolonged exposure to seawater in composite structures and their impact on fatigue performance. Thus, this study aims to investigate the effects of long-term exposure to natural seawater on both the fatigue strength and three-dimensional chemical changes of GFRP laminates. Fatigue tests were conducted under uniaxial cyclic loading at a stress ratio R = 0.1, considering three groups of specimens: a control group not immersed in natural seawater, a group immersed for 230 days in natural seawater, and a group immersed for 910 days in natural seawater. After the tests, fracture surfaces were analysed using scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). SEM examination revealed the microstructural occurrence of fibre-matrix debonding, reducing the load transfer between the fibre and matrix, contributing to the fatigue life decrease in immersed specimens. The fatigue results revealed that the reduction in fatigue life of the specimens immersed for 230 days was approximately 66 % of that observed in the control specimens increasing to 95 % when the immersion period extended to 910 days. Moreover, the effect of immersion time on the chemical structure of various regions within the specimens was assessed using Fourier-transform infrared (FTIR) spectroscopy. The main findings suggest the existence of a concentration gradient within the laminate and that regions near permeable surfaces are more vulnerable to chemical changes compared to regions located further away, even after reaching saturation.