Flexural Fatigue Research Articles

Mechanical properties and microstructure evolution of recycled sand concrete under high-frequency flexural fatigue load

In this paper, recycled sand (RS) was used in ballastless track concrete and the fatigue performance of recycled sand concrete (RSC) was studied. DIC and X-CT method were employed to investigate the fatigue strain and the microstructure evolution of RSC. The results indicate that the fatigue life of RSC follows the Weibull distribution. When the replacement ratio of RS in concrete is 50 wt.% (RSC40-50), the damage accumulation rate based on the fatigue strain is reduced by 12.7% and 7.0% compared to RS-free concrete (RSC40-0) and 100 wt.% recycled sand concrete (RSC40-100), respectively. The porosity of RSC exhibits a linear increase with loading cycles. Before fatigue loading, the porosity of RSC40-0, RSC40-50 and RSC40-100 was 0.91%, 1.08% and 3.01%, while it increased to 5.89%, 4.66% and 5.28% before the final failure. The increase in pore volume and the decrease in aspect ratio results in the formation of elongated pores and microcracks, ultimately leading to the fatigue failure.

Flexural Fatigue Performance of Hemp Fiber–Reinforced Concrete Using Recycled Concrete Aggregates as a Sustainable Rigid Pavement

Flexural Fatigue Performance of Hemp Fiber–Reinforced Concrete Using Recycled Concrete Aggregates as a Sustainable Rigid Pavement

Design of Two-Layer Roller Compacted Concrete with Joints by KENSLAB

Roller compacted concrete (RCC) is a type of rigid pavement that is designed in a similar way to conventional concrete pavements reflecting its mode of failure. The thickness design of RCC pavements is based on keeping the flexural stresses and fatigue damage in the pavement caused by wheel loads within allowable limits. As in all jointed concrete pavements, there is a greater effect from loads placed along edges and less at interior locations in the pavement. Joints in RCC pavement are clearly critical areas and form weak points. RCC is typically constructed with saw-cut joints to prevent random cracking, improve the appearance of the pavement surface, and maintain the highest possible load transfer across the joints. This paper presents an approach to designing the thickness of a two-layer RCC with induced cracks (i.e., joints) based on load transfer stiffness and fatigue damage, using the KENSLAB program to obtain pavement life, predict joint deterioration, and pavement damage.

A detailed investigation on assessing the introduction of hybrid fibres in Geopolymer composites for pavement application

ABSTRACT Geopolymer concrete (GPC) has been widely researched as an emerging sustainable construction material. As GPC possesses excellent mechanical and durability properties, it is highly recommended for the construction of rigid pavements. However, the brittle nature of GPC limits its utilisation in heavy traffic roads, reducing its fatigue life. This study aims to minimise the brittleness of Pavement quality GPC (PQGPC) by adding hybrid fibres (steel fibre + polypropylene fibre). Fresh, hardened and durability properties of hybrid fibre-reinforced pavement quality geopolymer concrete (HGPC) under ambient curing have been analysed. In addition, the experimental study also compared the flexural fatigue life of PQGPC with that of the best HGPC mix. Both fibres were added in the same % (by volume) up to a maximum dosage of 1.25% each. Results show that workability decreases with increased fibre addition, but compressive and flexural strength increases with an increment in the quantity of fibres up to 1%. It was observed that the abrasion resistance and shrinkage resistance also increase with the inclusion of hybrid fibres in HGPC. Fatigue results prove that the fatigue life of HGPC-3 (with 2% hybrid fibres addition) mix under medium and heavy loads is 40% and 28%, higher than PQGPC.

Effect of Flexural Fatigue Loading on Mechanical Properties, Permeability, and Rainstorm Resistance of Novel Pervious Concrete

Effect of Flexural Fatigue Loading on Mechanical Properties, Permeability, and Rainstorm Resistance of Novel Pervious Concrete

Flexural capacity and fatigue performance of full-scale FRP-concrete composite vehicular bridge girders

Since 2020, hybrid fiber reinforced polymer composite tub (CT) girders have been used in the construction of four in-service vehicular bridges in the United States and two additional bridges are under construction. However, despite their growing acceptance, there are very few FRP highway girder bridges throughout the world, only one full-scale destructive test of a CT girder has been conducted to-date, and girder fatigue life has not been explored. To provide additional strength data, a full-scale CT girder was manufactured and tested to failure in flexure. The results of this test confirmed the CT girder’s design efficiency, performance of its novel girder-deck shear connectors, and expected capacity determined through nonlinear moment-curvature analysis that accounts for the nonlinear compressive response and cracking of the concrete deck. A second identical CT girder specimen was subjected to 3,000,000 cycles of factored fatigue load and subsequently tested to failure in flexure to provide a direct assessment of cumulative fatigue damage. Full-scale fatigue tests of complex, vacuum-infused, hybrid glass-carbon members are unusual, making this test particularly valuable. The girder did exhibit damage accumulation during the first 1,500,000 cycles as evidenced by increasing deflection for the same applied load, but deflections remained relatively constant for the remaining cycles. The failure test of this specimen revealed a 33% loss in flexural strength due to flexural fatigue damage. However, the post-fatigue flexural strength still exceeded AASHTO capacity requirements by 43%, indicating a significant post-fatigue safety margin. The subsequent examination of girder fatigue life accounting for damage accumulation under realistic truck loading spectra indicates that in many applications, CT girder bridges have estimated fatigue lives in excess of 100 years, although caution must be exercised with when interpreting this result given that only one specimen was tested under specific laboratory conditions.

Assessing the flexural fatigue life of engineered cementitious composites exposed to freeze-thaw cycles

In cold regions, the infrastructure, particularly roads, bridges, and airport runways, faces prolonged exposure to the coupled effects of freeze-thaw (FT) cycles and fatigue loads. This makes the damage mechanism more complex, seriously affecting the durability of these structures. To investigate the influence of FT damage on flexural fatigue life, this study equated FT damage to the effect of increased stress levels and conducted FT cycles test, nuclear magnetic resonance test, and flexural fatigue test on engineered cementitious composites (ECC). The test results showed that the critical FT cycles number, predicted by using mass loss rate, relative dynamic elastic modulus, and porosity as characteristic parameters, was 507 cycles. The error in representing FT cycles using pore structure characteristic parameters was within 2.0 %. When the stress level S = 0.8, the flexural fatigue life gradually decreased from 22217 cycles to 724 cycles as the number of FT cycles increased. The Weibull distribution was used to obtain flexural fatigue life at different probabilities. Anderson-Darling test verified that the Weibull distribution is a reliable model for predicting material life. By equating FT damage to the effect of increased stress levels, the flexural fatigue equation based on different FT cycles number was established. The study found that the maximum error between the flexural fatigue equation and the Weibull-distributed flexural fatigue life was 18.76 %. Through the application of entropy weight method and grey relational analysis, it was found that the entropy weight grey incidence, euclidean grey correlation, fuzzy affiliation, and fuzzy grey correlation of stress level were 0.799, 0.888, 0.588, and 0.753, respectively. These values indicate that the influence of stress level on flexural fatigue life is greater than that of FT cycle numbers. This research aims to provide new insights for accurately calculating the flexural fatigue life of ECC in cold regions and improving the durability of structures.

Effects of Process Parameters and Process Defects on the Flexural Fatigue Life of Ti-6Al-4V Fabricated by Laser Powder Bed Fusion.

The fatigue performance of laser powder bed fusion-fabricated Ti-6Al-4V alloy was investigated using four-point bending testing. Specifically, the effects of keyhole and lack-of-fusion porosities along with various surface roughness parameters, were evaluated in the context of pore circularity and size using 2D optical metallography. Surface roughness of Sa = 15 to 7 microns was examined by SEM, and the corresponding fatigue performance was found to vary by 102 cycles to failure. The S-N curves for the various defects were also correlated with process window examination in laser beam power-velocity (P-V) space. Basquin's stress-life relation was well fitted to the experimental S-N curves for various process parameters except keyhole porosity, indicating reduced importance for LPBF-fabricated Ti-6Al-4V alloy components.

Analytical method of incorporating failure probability to predict the fatigue life of ultra-high-performance concrete (UHPC)

This study predicted the fatigue life (N) of UHPC incorporated with different volume fractions (Vf = 0.0%, 0.5%, 1.0%, 1.5% and 2.0%) of steel fiber under flexural cyclic loading at various stress levels (S). The Weibull distribution, a two-parameter model, was utilized to estimate the distribution of fatigue life in UHPC. Subsequently, three methods were employed to calculate the parameters: the graphical method, the method of moments, and the method of maximum likelihood. The averaged values of these parameters were then obtained to enhance the accuracy of the estimation. The results are presented in the form of S-N diagrams, which depict the quantitative relationship between stress (S) and fatigue life (N). This relationship was determined using the Wohler equation, the modified Wohler equation, and the power equation. By employing these equations, the flexural fatigue strength of UHPC can be accurately predicted. Subsequently, the fatigue failure probability (Pf) was incorporated to enhance the reliability of the S-N quantitative relation. The fatigue testing results were presented in the form of S-N-Pf curves, which comprehensively reflect the relationship between stress, fatigue life, and failure probability. Furthermore, the mathematical relation of the S-N-Pf curves was derived to predict the fatigue life of UHPC with a given failure probability, providing a more comprehensive and accurate assessment of its fatigue behavior.

Flexural fatigue behavior of ultra-high performance fiber reinforced concrete

Even though UHPFRC has been extensively utilized in infrastructures owing to its excellent mechanical properties, its fatigue behavior remains unclear because related research is very limited. In this study, the fatigue characteristics of UHPFRC were investigated using a four-point bending experiment. In this study, the fatigue characteristics of UHPFRC were investigated using a four-point bending experiment. To determine the fatigue load conditions, static tests were conducted at different loading speeds and ages before, during, and after the fatigue tests. The obtained mechanical properties exhibited a clear dependence on loading rate and age duration. Consequently, a loading frequency of 3 Hz, which is close to that experienced in real infrastructures, was employed in the fatigue tests. A linear S-N relation with a 0.87 fatigue endurance limit was obtained on a semi-logarithmic scale. Additionally, the fatigue life showed a close relationship with the initial cycle deformation. Correspondingly, threshold values of deformation indicators were proposed for predicting the occurrence of fatigue failure. Furthermore, a linear positive relationship was found between the density of multiple fine cracks and fatigue life, based on post-fatigue crack measurements using a microscope. The relatively narrow crack width compared to other cementitious composites demonstrated UHPFRC's superior resistance to corrosion factors. Consistent with the linear S-N relation, the structural degradation appears to be governed by a fiber slippage-to-pull mechanism, as no fiber rupture was observed.

Study on bending fatigue performance of recycled aggregate backfill subgrade

Recycled aggregate (RA), as a backfill subgrade material, has strong reproducibility and environmental protection, which cannot only effectively reduce resource consumption and environmental pollution but also achieve recycling of resources. Therefore, a study on the bending fatigue performance of RA backfill subgrade is proposed. Based on linear elastic state, softening state, and damage accumulation state, the variation law of bending fatigue damage variables is analyzed, and the stiffness of RA under cyclic load is calculated. According to the correlation between fatigue damage corresponding to two different load links and the constitutive relationship of RA, the identification results of bending fatigue damage state based on RA backfilling subgrade is obtained. The advantages of the fatigue damage model of RA are analyzed, and the fatigue life equation is established based on the damage evolution equation. Strain, stiffness modulus, asphalt saturation, and asphalt mixture adjustment coefficient are selected as model parameters to establish the fatigue damage model of RA. The flexural bearing capacity of the double-reinforced rectangular section is calculated, and the flexural fatigue performance of RA backfill subgrade is analyzed. The test results show that the high stress level in this method leads to a sharp decline in the fatigue life of the specimen, and the influence of fatigue damage gradually appears, which is helpful to improve the durability and safety of the subgrade structure. The range of change shows a small range, which is close to the reduction coefficient result, indicating that this method has high reliability in analyzing the bending fatigue performance of RA backfill subgrade.

Build Orientation Effect on Bending Fatigue Performance and Impact Toughness of Laser Powder Bed Fusion Manufactured Ti6Al4V Without Heat Treatment

Titanium alloys are highly valued in various industries due to their exceptional qualities. This study examines how the build orientation affects the mechanical and fatigue properties of Laser Powder Bed Fusion (PBF-LB) produced Ti6Al4V, without heat treatment. The research shows mechanical properties vary based on build orientation with vertically oriented specimens exhibiting the highest yield and tensile strengths, while vertical orientation excels in ductility, measured through elongation at break. Impact toughness sees variations with horizontal orientation performing the best. However, build orientation has minimal influence on flexural bending fatigue performance. Both diagonal and vertical orientations show similar fatigue limits at around 40 MPa. Dry electropolishing proves to be an effective technique, significantly enhancing fatigue performance with limits stabilizing at about 150 MPa. This study underscores the importance of considering build orientation in PBF-LB manufacturing for specific mechanical and impact properties and the potential of dry electropolishing in improving the fatigue performance of Ti6Al4V components. These findings offer valuable insights for the additive manufacturing industry, aiding in the optimization of Ti6Al4V component production.

Bending Fatigue Properties of Ultra-High Toughness Cementitious Composite (UHTCC).

Ultra-High Toughness Cementitious Composite (UHTCC) represents a composite material meticulously engineered on the foundation of micromechanical principles. The multi-crack cracking and strain-hardening characteristics of UHTCC enable it to be applied to orthotropic steel decks to control the crack width. Different from most studies which only focus on hybrid fiber or fatigue characteristics, this paper studies the influence of hybrid fiber content on static mechanical properties, flexural toughness, and flexural fatigue characteristics of UHTCC under different stress levels. The compressive and flexural strength, bending toughness, and fatigue damage of UHTCC under different fiber ratios were compared, and the fatigue properties of hybrid fiber UHTCC were verified. The results reveal that hybrid fiber exerts a more pronounced effect on toughness, augmenting the maximum folding ratio by 23.7%. Single-doped steel fiber UHTCC exhibits a characteristic strain-softening phenomenon attributable to inadequate fiber content, whereas the bending toughness index of hybrid fiber UHTCC surpasses that of SF1.5P0 by 18.6%. Under low-stress conditions, UHTCC demonstrates a nearly threefold increase in bending fatigue life with a mere 1% steel fiber content, while the influence of polyvinyl alcohol (PVA) fiber on fatigue life is more significant: with an increase of only 1/5 volume content, the fatigue life increased by 29.8%, reaching a maximum increase of 43.2% at 1/4 volume content. Furthermore, the fatigue damage accumulation curve of UHTCC follows a three-stage inverted S-shaped trajectory. The inclusion of PVA fiber facilitates early initiation of stable cracking during the fatigue failure process, thereby advancing the entire strain stability development stage and mitigating external load forces through the proliferation of micro-cracks. Consequently, compared to SF1P0, the ε0 of SF1P5 experiences a significant increase, reaching 143.43%.

Variability of strength and stiffness assessment for non-profile beam structures

Introduction. Traditional ways to increase the structural strength and stiffness of beams are now almost exhausted, and optimization of production and operation technologies is mostly based on the use of new materials and increasing their reliability as bearing elements of a complex geometric profile. Bearing elements of building structures operate under high loads and, even despite their predominantly static nature, experience a complex volumetric stress and strain state, which can scarcely ever be confirmed empirically and statistically.Aim. To propose an approach to assessing the strength and stiffness of beam structures operating under conditions of transverse bending of a complex geometric profile.Materials and methods. Classical energy methods, including Castigliano, Maxwell–Mohr and Vereshchagin methods (moment area method), have been used to assess the strength and stiffness of non-profile beam structures, initial parameters, differential equations of the deflection curve.Results. The similarity parameters (fitting criteria) of Mises–Hencky and Zhurkov reflect the behavior of a brittle or plastic beam material reasonably well. These characteristics are proposed to be combined in the Arrhenius–Zhurkov durability functions.Conclusions. The dependencies given in the calculations can be recommended for improving the flexural static and fatigue strength, as well as the stiffness of the bearing elements of building structures.

Investigation on the fatigue crack propagation of rock-concrete interface under fatigue loading below the initial cracking load

The fatigue crack propagation of the composite rock-concrete interface under constant-amplitude flexural fatigue loading below the initial cracking load was investigated in the present study. Fatigue pre-crack initiation and propagation tests were first conducted on three types of rock-concrete interfaces under three-point bend loading. It was shown that for the rock-concrete interface, the damage evolution throughout the fatigue loading process can be divided into deceleration and acceleration stages according to the rate curves of flexural stiffness, deformation and crack propagation. The crack propagation rate exhibited two distinct regions when plotted on a log scale, namely the small-crack growth region and the long-crack growth region. The small-crack growth region for the studied rock-concrete interfaces was not particularly pronounced. The long-crack growth region was the Paris’ law region and included both the acceleration and part of the deceleration stages. Based on the experimental results, the fatigue crack propagation rate in the Paris’ law region was then described using the empirical Paris’ law. The exponent m1 in the Paris’ law was found to be approximately constant, with a value of m1 ≈ 21 for the rock-concrete interface. The pre-factor C1 was found to be dependent on both the load ratio R and the type of the rock-concrete interface (represented by an elastic mismatch parameter α). By introducing R and α into the empirical Paris’ law, an adjusted Paris’ law was proposed. The adjusted Paris’ law can describe the fatigue crack propagation rate in a unified way for the same rock-concrete interface of different R and different interfaces in the scope of this research. Based on the adjusted Paris’ law, the fatigue cycles during the crack propagation and fatigue lifetimes of all tested rock-concrete interface specimens were reasonably predicted. For practical applications, an approach was suggested involving a combination of the adjusted Paris’ law and a material coefficient β (approximately β ≈ 0.143 in this study) to estimate the fatigue lifetimes of structures or specimens with existing pre-cracks at the rock-concrete interface.

Experimental study on the flexural fatigue performance of slag/fly ash geopolymer concrete reinforced with modified basalt and PVA hybrid fibers

Geopolymer, owing to its inherent low-carbon emission advantages, emerges as a potential substitute to diminish reliance on high-carbon-emitting Portland cement. Nonetheless, similar to ordinary Portland cement concrete, geopolymer concrete tends to exhibit brittle fracture under cyclic bending loads. To improve its flexural fatigue performance, this paper incorporated the modified basalt (MB) fiber and PVA fiber in hybrid form into the geopolymer concrete. The flexural fatigue behavior of hybrid fibers reinforced geopolymer concrete was investigated, with a focus on the influence of varying hybrid fibers volume fractions. Digital Image Correlation technology was utilized to accurately track the evolution of crack length and the local strain field during the fatigue failure process. The results revealed that the incorporation of both MB and PVA fibers effectively delayed the initiation and propagation of cracks, leading to a more complex path of fatigue cracks. The PVA fiber demonstrated significant efficacy in inhibiting microcracks, while the MB fiber played a crucial role in controlling the expansion of macroscopic cracks. When the proportion of MB fiber was predominant in the hybrid mix, the crack development pattern mirrored that of samples containing MB fiber alone, exhibiting a greater extent of crack length. At a volume fraction of 0.9% for MB fiber and 0.2% for PVA fiber, a significant improvement in the fatigue life of the concrete was observed, resulting in a remarkable 136.23% increase compared to the control. This study has developed geopolymer concrete featuring enhanced crack resistance and superior flexural fatigue endurance under cyclic loading, promoting the application of environmentally friendly building materials in practical engineering.

Improved mechanistic performance of natural rubber latex modified pavement concretes in sulfate environments

ABSTRACT Sulfate attack causes significant degradation in the concrete matrix, including softening, expansive cracking, and other disruptive processes. This research examined the impact of incorporating a Natural Rubber Latex (NRL) additive on the mechanical and durability improvement of concrete pavements. The study evaluated the influence of water to cement (w/c) ratios and dry rubber to cement (r/c) ratios on compressive and flexural strengths, as well as flexural fatigue characteristics, before and after immersion in a 5% sulfate solution at various intervals. Optimal r/c ratios for the highest flexural strength and fatigue life were 0.58, 1.16, and 1.73 for w/c ratios of 0.3, 0.4, and 0.5, respectively. The highest durability was achieved at an r/c ratio of 5.78, resulting in a compressive strength loss of 4.2–7.7 times lower compared to that of normal concrete, hence extending the service life against severe environment. The fatigue model equation proposed by the Portland Cement Association (PCA) was utilised to predict the fatigue life of both normal and NRL-concretes. The outcome of this research will lead to a fundamental knowledge in the development of a design guideline of sustainable concrete pavements, and eventually promote the usage of NRL, which is abundant in Southeast Asia, including Thailand.

Optimizing the Utilization of Steel Slag in Cement-Stabilized Base Layers: Insights from Freeze-Thaw and Fatigue Testing.

This paper presents a study on the mechanical properties of cement-stabilized steel-slag-based materials under freeze-thaw cycles for a highway project in Xinjiang. Using 3D scanning technology the specimen model conforming to the real steel slag shape was established. The objectives of the study are as follows: to explore the sensitivity between the macro- and micro-parameters of the specimen and to establish a non-linear regression equation; and to study the changes in mechanical properties of materials under freeze-thaw cycles, fatigue loading, and coupled freeze-thaw cycle-fatigue loading. The results show that there are three stages of compression damage of the specimen, namely, linear elasticity, peak plasticity, and post-peak decline. Maximum contact forces between cracks and particles occur mainly in the shear zone region within the specimen. The compression damage of the specimen is a mixed tensile-shear damage dominated by shear damage. When freeze-thaw cycles or fatigue loads are applied alone, the flexural strength and fatigue life of the specimens show a linear relationship of decline. The decrease in flexural modulus at low stress is divided into the following: a period of rapid decline, a relatively smooth period, and a period of fracture, with a tendency to change towards linear decay with increasing stress. In the case of freeze-thaw-fatigue coupling, the flexural modulus of the specimen decreases drastically by about 50% in the first 2 years, and then enters a period of steady decrease in flexural modulus in the 3rd-5th years.

Improvement of fatigue life of Ti-6Al-4V alloy treated by double-sided symmetric oblique laser shock peening

To improve the anti-foreign object damage (FOD) ability of Ti-6Al-4V alloy blisk blades, a blade simulation specimen was designed and subjected to double-sided symmetrical oblique laser shock peening (DSOLSP) treatment. Surface roughness, residual stress distribution, and microstructural evolution of simulated specimens of Ti-6Al-4V alloy without and with DSOLSP were investigated, and the strengthening effect was evaluated by flexural fatigue test. The results showed that after DSOLSP treatment, surface roughness of simulated specimens was reduced from Ra0.97 µm to Ra0.6 µm. DSOLSP treatment generated a compressive residual stress (CRS) field along the entire thickness direction of the simulated specimen. Nanostructures with a depth of ∼500 nm was observed at topmost surface layer, and the average size of the nanograins was about 35.2 nm. Compared with the base material, the flexural average fatigue life of the simulated specimen was increased by 8.45 times. Moreover, mathematical statistical analysis confirms that DSOLSP has a significant effect on the fatigue life of simulated samples. The development of CRS fields throughout the entire thickness direction, the grain refinement on the surface, and the reduction of surface roughness are primarily responsible for the enhancement of the flexural fatigue life of the DSOLSP simulated specimen.

Flexural fatigue performance of recycled sand concrete for high-speed railway track bed

To investigate the applicability of recycled sand concrete in high-speed railway ballastless track bed, in this study, the fatigue life, strain evolution curve and calculated stiffness of C40 concrete incorporating 0, 50 % and 100 % recycled sand were explored. Digital image correlation (DIC) and the nanoindentation test were used to explore the influence of recycled sand on the performance of concrete. The results show that the flexural fatigue life of recycled sand concrete conforms to a two-parameter Weibull distribution. The fatigue strain progression and calculated stiffness demonstrate a distinct three-stage trend. Compared to natural aggregate concrete, the first-stage strain contribution of recycled sand concrete decreases by approximately 10 %. With the increase of fatigue cycles, the calculated stiffness decreased significantly, the dissipated energy increases gradually. Compared with recycled sand-free concrete and full recycled sand concrete, the concrete containing 50 % recycled sand possesses the highest elastic modulus and lowest thickness of the interfacial transition zone (ITZ), thus the average fatigue life of recycled sand concrete increased by 4.9 and 10.2 times.