Cyclic Loading Research Articles

Surface condition driven fatigue performance of laser powder bed fusion H13 steel

Surface variation is an inherent imperfection in the laser powder bed fusion (LPBF) processed samples, comprising of primary roughness (PRR) from the melt pool solidification and secondary roughness (SER) from adhered powder particles. Components under cyclic loading are sensitive to surface defects, making surface finishing crucial for fatigue-bearing parts. However, this undermines LPBF’s advantage of creating high-performance and geometrically complex components. This study examines the effect of surface roughness on fatigue crack initiation in LPBF H13 steel, a high-strength alloy with a tensile strength of 1800 MPa. The focus is on scenarios where contour scanning strategies are not employed. Vertically deposited samples were subjected to three surface conditions: as-built (AB) with PRR + SER, half-polished (HP) with only PRR, and well-machined (M) with no PRR or SER. Optical and digital surface roughness characterization and stress-controlled fatigue testing were performed. Results revealed that while AB-samples showed significantly rough surface compared to HP-samples, their fatigue performance did not reduce. In contrast, M-samples had a slight improvement in roughness but exhibited a fatigue life increase by a factor greater than 17. This was attributed to the PRR, specifically the solidification valleys between the neighboring melt pools. Factographic analysis showed that the PRR-driven fatigue crack initiation is a critical determinant of fatigue performance.

Effect of impact loading and acidic drying-wetting cycles on fragmentation and energy dissipation characteristics of sandstone

Effect of impact loading and acidic drying-wetting cycles on fragmentation and energy dissipation characteristics of sandstone

A new design approach for predicting the required lap-splice length for new generation GFRP bars in concrete members under reversed cyclic loading

A new design approach for predicting the required lap-splice length for new generation GFRP bars in concrete members under reversed cyclic loading

Application of the Cyclic Strain Accumulation Method on Shallow Foundations under Eccentric Cyclic Loading in Sand

Application of the Cyclic Strain Accumulation Method on Shallow Foundations under Eccentric Cyclic Loading in Sand

Glass Fiber-Reinforced Polymer-Reinforced Concrete Columns with Varied Concrete Strength under Combined Bending-Torsion Cyclic Loading

Glass Fiber-Reinforced Polymer-Reinforced Concrete Columns with Varied Concrete Strength under Combined Bending-Torsion Cyclic Loading

Seismic performance on PSPC beam - concrete encased CFST column frame with a built-in reduced beam section

The concrete-filled steel tubular (CFST) column is widely used to connect with a steel beam owing to the quick dry connection and acceptable seismic performance. Therefore, a partially steel-reinforced precast concrete (PSPC) beam with an embedded H-beam was developed to combine the merits of both the prefabrication in the precast concrete beam and the quick assembly in the steel beam. In this study, the developed beam was proposed to connect the concrete encased CFST column with a reduced beam section. A half-scaled frame substructure specimen with two floors and two bays was designed and tested under the cyclic loading to investigate the seismic performance. A series of seismic properties were analyzed, including the failure phenomena, hysteretic performance, stiffness degradation, and energy dissipation capacity. The dog-bone configuration was found to benefit the beam hinge failure mechanism and an acceptable deformation capacity (the ductility coefficient up to 2.77). The function of the H-beam contributed to stable energy absorption (the equivalent damping coefficient from 0.33 to 0.37). Finally, the proposed frame was compared with a reinforced concrete frame and a steel-reinforced concrete frame through numerical analysis. The partial steel-reinforced configuration had a positive influence on the bearing capacity, hysteretic performance, and safety storage. In addition, it could improve the cost-effectiveness with little decrease in the bearing capacity.

Basic Study on the Proposal of New Measures to Improve the Ductility of RC Bridge Pier and Their Effectiveness

To enhance the seismic performance of reinforced concrete (RC) elements, it is essential to consider both strength and ductility post-yielding. This study proposed a novel method to improve the ductility of RC piers by using preformed inward-bending longitudinal reinforcements at the plastic hinges. Two full-scale model tests of standard and ductility-enhanced (DE) RC piers and numerical simulations were conducted. The lateral reversed cyclic loading experiments were conducted to assess the effectiveness of this new approach. The performance was evaluated regarding failure mode, plastic hinge distribution, hysteretic properties, normalized stiffness degradation, normalized energy dissipation capacity, bearing capacity, and ductility. Non-linear finite element method (FEM) analyses were also carried out to investigate the usefulness of the proposed method by DIANA, and simulation was validated against the experiment results by hysteretic curves, skeleton curves, failure mode crack pattern, ductility coefficient, and bearing capacity. The results indicated that the proposed method enhanced bearing capacity, resistance to stiffness degradation, energy dissipation capacity, and ductility. Additionally, it was observed that the preformed positions and curvature of the main steel bars influenced the plastic hinge location and the buckling of longitudinal reinforcements. FEM analysis revealed that it might be reasonable to deduce the other factors that influenced the ductility of the specimens by using the same material parameters and models.

Anisotropy and lateral compressive strength of large-size cement-stabilized macadam for bulging deformation resistance: A numerical analysis

Large-size cement-stabilized macadam (LCSM) base effectively hinders bulging deformation in asphalt pavements. Under vibratory compaction, the embedded skeleton structure and anisotropy of large-size aggregates (LSA) impact the mechanical properties of LCSM mixes. To reveal the mesostructure and anisotropy of LSA and determine the optimal volume percentage of LSA in LCSM mixes against bulging deformation, this study first characterized the bulging deformation resistance of LCSM mixes using lateral compressive strength (LCS). Next, the evolution of coordination number (CN) and distributions of contact force and contact normal for LSAs at different volume percentages under dynamic cyclic loading were investigated using the discrete element method (DEM). In particular, the induced anisotropic behavior was explored. Then, indoor tests and numerical simulations were conducted to assess the mixes’ LCS and vertical compressive strength (VCS); additionally, the compressive damage characteristics were analyzed. The results indicate that increasing the volume percentage of LSA and dynamic cyclic loading enhanced the CN, strong contact force, and contact normal density. LSAs at varying volume percentages exhibited pronounced anisotropic characteristics before and after loading, and the anisotropy factor of the LSA dropped after loading at a volume percentage of 65 %. Furthermore, the mixes’ VCS values exceeded LCS ones at the same LSA volume percentage, and there was a consistent relationship between the LSA anisotropy and the VCS/LCS ratio, suggesting that the optimal LSA volume percentage in LCSM mixes ranged from 60 % to 65 %. Finally, as the LSA volume increased, the skeleton effect became more pronounced than the interface attenuation effect, leading to higher VCS and LCS values in the mixes, thus improving their resistance to bulging deformation.

Effect of cyclic loading on microstructure and plastic deformation in heat-treated Co–28Cr–6Mo alloy fabricated via laser powder bed fusion: an in situ synchrotron X-ray diffraction study.

We present a systematic microstructure-oriented plasticity investigation of an additively manufactured cobalt-based alloy aiming to relate microstructural changes to the fatigue resistance. A load-controlled cyclic test in the low-cycle fatigue regime was utilized to study mechanical response and microstructural changes in the alloy after reverse phase transformation heat treatment. Deformation-induced FCC → HCP phase transformation was followed using in situ synchrotron X-ray diffraction combined with ex situ electron backscatter diffraction and scanning electron microscopy. Scanning transmission electron microscopy provided experimental evidence of the presence of precipitates in the solution annealed sample. It was found, that a stepwise increase in plastic deformation is attributed to nucleation and growth of different martensitic crystallographic variants. These insights into plasticity and microstructural changes suggest that the reverse phase transformation heat treatment is an effective approach for improving the fatigue resistance of low stacking fault energy alloys, that are susceptible to deformation-induced martensitic transformation.

Stiffness degradation and mechanical behavior of microfiber-modified high-toughness recycled aggregate concrete under constant load cycling

The mechanical properties of High-Toughness Recycled Aggregate Concrete (HTRAC) were investigated in this study as an innovative and environmentally friendly construction material, along with its potential applications in structural stability. Small-scale specimens with six levels of micro-steel fiber content were made, and a series of cyclic tests with constant loads were carried out. Using In-Situ 4D CT technology, the damage characteristics of the microstructure of HTRAC and the reinforcing effects of fibers on key mechanical parameters (peak stress, peak strain, ultimate strain, post-peak modulus, and toughness indicators) were analyzed. A comprehensive fiber reinforcing factor calculation model was proposed to assess its contribution to strength, deformability, and toughness, and the correlation between the number of cyclic loadings and stiffness degradation was also quantified. it is confirmed that HTRAC exhibits a significant advantage in toughness compared to traditional recycled aggregate concrete (RAC). The findings of this study provide crucial technical support for the further development and application of HTRAC, indicating its promising prospects in the field of sustainable construction materials

Research on fatigue life of carbon fiber reinforced polymer strengthened single-sided butt welded joints utilizing resin pre-coating for strong adhesive bonding

Single-sided butt welding is a common connection method used in box beam structures such as excavator booms. Single-sided butt weld joints are prone to fatigue failure since the structures are subjected to cyclic loads over extended periods. The purpose of this study is to improve the fatigue performance of single-sided butt welded joints. Carbon fiber reinforced polymer (CFRP) strengthened single-sided butt welded joint specimens with permanent backing plates were prepared by pre-coating method, and constant-amplitude tension–tension fatigue tests were carried out on the specimens. The effects of welding groove parameters and CFRP reinforcement on fatigue life were studied. The test results show that the CFRP-strengthened specimens without blunt edges and with a groove angle of 40° show the highest average fatigue life. The single-sided bonding of 10 layers of CFRP sheets effectively inhibits the propagation of fatigue cracks and significantly improves the fatigue life of welded joints. In the CFRP/welded joint composite structure, the strain monitoring results show that the peak strain of the interface is the largest in the middle position, and the peak strain rises sharply in the rapid crack propagation stage, which indicates that the real-time interface strain peak can reflect the fatigue crack propagation. It provides an early warning method for real-time monitoring of fatigue life failure of welded structures in practical engineering.

Temporal Homogenization Modeling of Viscoelastic Asphalt Concretes and Pavement Structures under Large Numbers of Load Cycles

Temporal Homogenization Modeling of Viscoelastic Asphalt Concretes and Pavement Structures under Large Numbers of Load Cycles

Influence of steam curing on cyclic triaxial characteristics of recycled aggregate concrete: Experimental analysis and DEM simulation

The engineering application of steam-cured recycled aggregate concrete (often in a cyclic triaxial stress state) can not only improve the recycling efficiency of resources, but also accelerate the construction progress. In this paper, we adopt a combination of laboratory experiments, theoretical analysis and numerical simulation to study the cyclic triaxial characteristics of recycled aggregate concrete (RAC) under different curing regimes (20℃, 40℃, 60℃ and 80℃). The results indicate that as the steam curing temperature increases, the internal damage caused by high temperature continues to intensify, and the cyclic triaxial failure mode of RAC transitions from shear failure to compression failure, and its peak strength, dynamic elastic modulus, and dilatancy angle all show a downward trend. A linear prediction model is established based on the strong correlation between peak strength and steam curing temperature. As the loading cycles increase, the dynamic elastic modulus and dilatancy angle of RAC show exponential and linear downward trends respectively, and the decline rate increases with the increase of steam curing temperature, and the prediction models for dynamic elastic modulus and dilatancy angle are established based on quantitative relationships between variables. On the basis of experimental analysis results, a cyclic triaxial DEM model considering real recycled aggregates is established by introducing steam-cured damage indexes into the mesoscopic parameters, and its applicability in predicting cyclic triaxial mechanical properties of RAC under different curing regimes is verified. The research outcomes can save a lot of test cost and time consumption for developing steam-cured concrete with better performance, and have important theoretical guidance and practical significance for the wide application of steam-cured concrete.

Performance Investigation of Diatomite Modified Asphalt Mixtures for Different Diatomite Ratios and Grinding Sizes

Modification of asphalt mixtures has become almost mandatory today due to increased stresses in pavements, shortening of load cycle times, and decreases in binder quality. For this reason, many additives can be added to bitumen or asphalt mixture. Industrial material wastes can also be among these additives. When diatomite material is used as a performance enhancer in asphalt mixtures, it significantly improves the main performance indicators of the asphalt mixture. However, low temperature cracking of diatomite-modified asphalt mixtures is still controversial in the literature. This study evaluated the asphalt mixture in terms of low-temperature cracking, water damage, and rutting, depending on the diatomite grinding size (gradation) and addition ratio. Three different sizes of diatomite additives (106, 212 and 300-micron maximum diameter) were used at three addition ratios (5, 10 and 15% by weight of bitumen). According to the test results, it was seen that the mechanical properties of asphalt mixtures were significantly affected by the addition ratios and diatomite sizes, and the use of 300-micron maximum diameter diatomite at the rate of 10% and 15% was more effective. However, according to the BBR test results, the use of diatomite additives with a maximum size of 106 µm at 5% slightly increased the low temperature cracking resistance.

A New Method for Predicting Dynamic Pile Head Stiffness Considering Pile–Soil Relative Stiffness Under Long-Term Cyclic Loading Conditions

Under long-term horizontal cyclic loading, the evolution characteristics of the loading and unloading stiffness of piles are an important representation of pile–soil interaction. However, research in this area is limited, particularly regarding the impact of factors like pile–soil relative stiffness. In this study, laboratory tests with a long-term horizontal cyclic loading strategy were conducted to study various factors, including different cyclic amplitude ratios (ζb), cyclic load ratios (ζc), and pile–soil relative stiffness (T/L) in sandy soil, on dynamic pile head stiffness. The results show that the normalized cumulative displacement increases with the number of cycles and the ratio of T/L but tends to decrease as ζc increases. As ζb increases, the normalized cyclic loading stiffness also rises, while it has little effect on the normalized cyclic unloading stiffness. On the other hand, as ζc or T/L increases, the cyclic loading stiffness increases while the unloading stiffness decreases. Based on these observations, prediction formulas for normalized cumulative displacement and cyclic loading and unloading stiffness were established and confirmed with test results. The findings of this study provide methodological references for establishing models of pile–soil interaction under cyclic loading and for predicting loading and unloading stiffness under different influencing factors.

In-Plane Cyclic Mechanical Properties of CF/PEEK/TPU Flexible Composite with Zero Poisson Ratio.

This paper presents the in-plane deformation and cyclic mechanical properties of CF/PEEK (Carbon Fiber-Reinforced Polyetheretherketone)-reinforced TPU (thermoplastic polyurethanes) flexible composites with a zero Poisson ratio. A novel CF/PEEK honeycomb reinforcement with a zero Poisson ratio was fabricated by using 3D-printing technology. Then, TPU was bonded in the two sides of the CF/PEEK honeycomb reinforcement. The in-plane deformation ability and cyclic mechanical properties were evaluated. The results show that the zero Poisson ratio flexible composite can achieve a large in-plane plastic deformation of more than 50% and can better maintain the zero Poisson ratio superstructure. By collecting and comparing the mechanical characteristic values of the CF/PEEK flexible composite under a cyclic load, the CF/PEEK flexible composite MH22-t0.6-CT has the best structural stability. The length of the structure was increased by about 12.53%. By studying the deformation mechanism and failure mechanisms of the flexible composites, the in-plane recyclability of the flexible composites was evaluated, which provides the basic research basis for large-scale in-plane deformation composites.

Ion Identification and Ultralow Concentration Sensing with Liquid Flexoelectricity.

The isolation and concentration of electrical charges at ionic-electronic interfaces are prevalent phenomena that impede effective communication between ionic and electronic systems. Detecting these concentrated charges at the interface is crucial for applications, such as signal transmission and ion detection. Current electrical detection approaches introduce additional ionic-electronic interfaces via metallic electrodes with an external stimulating voltage, which alters the initial ion distributions at the interfaces. In this work, we introduce the flexoelectricity of liquids to examine the electrical charge aggregation at ionic-electronic interfaces under cyclic mechanical loads. The measured electrical responses reflect the coupling phenomena between the flexoelectricity and the electric double layer. This proposed approach demonstrates the capability to quantify ion types and concentrations at interfaces. Furthermore, it can identify ion types in mixed solutions and offers high sensitivity at ultralow concentrations. This work promotes a nonchemical, general mechanical method for charge detection at ionic-electronic interfaces.

Cyclic Performance of Reinforced Concrete Columns Strengthened with Basalt-Fibre-Reinforced Cementitious Matrix (BFRCM)

The purpose of this experimental investigation was to confirm whether the Basalt-Fibre-Reinforced Cement Matrix (BFRCM) effectively enhances the cyclic performance of columns made of reinforced concrete (RC). The BFRCM system, which comprises basalt fabric mesh reinforced with a cementitious matrix containing polyvinyl alcohol (PVA) fibre, has significant practical implications. In the testing phase, concrete and steel reinforcement were used to create RC column specimens, which were then strengthened with three, four, and five layers of BFRCM. The horizontal cyclic and constant axial loads were applied and tested to evaluate the performance of RC columns with and without strengthening. By improving the energy dissipation by approximately 9 to 32% and increasing stiffness by roughly 24 to 44%, the column specimen with three, four, and five layers of BFRCM performed better than the control specimen. Furthermore, incorporating short fibre into the matrix effectively improved the tensile properties of the FRCM systems and decreased the shrinkage-induced cracks. The increased stiffness indicates that the column with BFRCM has better structural strength because it can sustain higher loads with less deflection. The thorough comparative analyses examined the RC column specimens’ failure modes, hysteretic responses, stiffness degradation, and energy dissipation, providing a reliable basis for the conclusions. The test results confirmed that the BFRCM effectively enhanced the seismic capabilities and has been promised a way to strengthen RC elements, providing valuable insights for civil engineering and materials science.

Experimental study on the seismic behavior of a novel type of precast column‐steel beam connection with grouted corrugated metallic duct

AbstractConsidering the complicated joint details and installation difficulties of beam‐column joints, a novel type of precast joint that utilizes grouted corrugated metallic ducts was proposed. Four full‐scale specimens were prepared and subjected to the low cyclic loading test, including two precast specimens (interior beam‐column joint and exterior beam‐column joint) and two cast‐in‐place specimens for comparison. The seismic behavior of the joint was evaluated based on failure modes, hysteretic behaviors, ductility, bearing capacity, and energy dissipation. From the test results, all specimens experienced bending failures at the beam end, which kept the plastic hinge away from the joint core area. The precast assembly joints showed excellent seismic behavior, especially in terms of the bearing capacity, ductility, and energy dissipation capacity, which are better than the cast‐in‐place ones. The bearing capacity measured for each specimen was greater than the design standard, indicating that the joints are reasonably designed, and the members are safe and reliable. Parametric analysis was also conducted by finite element modeling and design advice was given accordingly.

Evaluation of the Mechanical Properties and Fatigue Resistance of the ZrO2CeYAl2O3 Composite

This work aimed to evaluate the fatigue limit of the zirconia ceramic composite stabilized with yttria and ceria reinforced with alumina platelets (ZrO2CeYAl2O3) and characterize the mechanical properties of sintered specimens. Bar-shaped specimens were compacted by uniaxial pressing in a rigid die and sintered at 1500 °C-2 h. Subsequent characterizations included quantitative phase analysis by X-ray diffractometry, determination of density, modulus of elasticity, microhardness, fracture toughness, four-point flexural strength, and fatigue limit. Observations of fracture mechanisms were carried out using confocal and scanning electron microscopy (SEM). The sintered samples presented values above 98% of relative density. Complex microstructures with equiaxed, homogeneously distributed submicrometer grains and planar alumina platelets were observed by SEM. The composite samples showed high values of fracture toughness due to the transformation, during the test, from the tetragonal to monoclinic phase, causing an increase in volume and creating compression zones around the crack, making it difficult to propagate. The average flexural strength reached 445.55 MPa, with a Weibull modulus (m = 16.8), revealing low flexural rupture stress data dispersion. In the composite evaluated in this work, the occurrence of the tetragonal → monoclinic transformation that occurs in the Ce-TZP present at the triple points and grain boundaries during cyclic loading produces “crack tip shielding”, that is, a restricted elastic zone (zone shielding) that surrounds the crack tip. This phenomenon leads to a reduction in the stress intensity factor at the tip of the crack and slows down its growth, generating an increase in the fatigue resistance of the composite.