Damage Evolution Research Articles

Monitoring a mass timber—BRB braced mass timber frame under cyclic loading via acoustic emission

This article focuses on the acoustic emission (AE) monitoring of a new type of mass timber buckling restrained brace (T-BRB), consisting of a wood casing made of mass plywood panel and a steel core embedded in the casing, for improving seismic resilience of mass timber structures. The casing secures the steel core through a series of bolts. To investigate the failure mechanisms of T-BRBs, two cyclic loading tests are conducted on a mass timber frame braced by T-BRBs with and without carbon fiber-reinforced polymer wraps, and an AE system is deployed for structural health monitoring (SHM). Multiple AE signatures are analyzed to infer the yielding point and failure modes of the T-BRB. AE features, including AE hit rate and cumulative energy, can successfully identify the ultimate structural failures. Results from AE hits and measured area of rectified signal envelope (MARSE) per quarter cycle suggest that the first significant feature values correspond to the cycle when the embedded steel core yielded. The b-value analysis demonstrates a general decreasing trend through the loading process and can characterize the evolution of structural damages. By evaluating both the strain energy and AE energy to reflect damage severity, the sentry function can identify the load cycle of steel core yielding and ultimate structural failure. As the first work applying AE monitoring on structural experiments of T-BRB, this research provides general guidances for SHM of T-BRB braced mass timber structures.

Numerical Analysis on the Excavation Damage Evolutions of Layered Tunnels: Investigations on the Influences of Confining Pressure and Layer Angles.

The bedding structure of layered tunnels has a significant impact on the evolution of excavation damage, yet research on the relevant evolution mechanisms is scarce. In view of this, this paper develops a mesh-free numerical method to simulate the progressive damage process of tunnel excavation and proposes a method for applying stress boundaries within the SPH framework. Through this method, simulations of tunnel excavation damage under different bedding dip angles and stress ratios are conducted. The results show that the following: in the simulation of excavation damage of a tunnel without bedding structures, specific areas around the tunnel exhibit characteristics of tensile-shear composite failure and shear failure, verifying the rationality of the algorithm; under different bedding dip angles, a damage zone is first generated around the tunnel, and shear cracks appear at the tangent of the bedding plane and the tunnel, with the damage degree being the largest when α = 30° and the smallest when α = 45°; and under different stress ratios, the damage starts around the tunnel, continuously evolves, and finally forms a failure zone inside the bedding plane joints tangent to the tunnel, and the damage degree increases with the increase in the stress ratio. This study discusses the damage mechanisms under different calculation schemes and provides a reference for understanding the excavation damage mechanisms of layered tunnels.

Test and simulation of high temperature resistant polyamide composite with single lap single bolt connection

The advancement of next-generation aerospace vehicles has presented new requirements and challenges for ensuring the structural integrity of aircraft components in extreme environments. Consequently, the utilization of high temperature resistant polyamide composite materials has become pivotal in the manufacturing of aerospace vehicle parts that operate under high temperatures (250 °C). As a critical connection technology for these materials, the mechanical behavior of bolted connection structures under high temperatures requires further investigation. In this paper, a combination of experimental and numerical simulation is used to investigate the load carrying capacity and failure mechanism of T700/BMP316 composite bolted joints at room temperature and 250 °C. The experimental results show that the ultimate load carrying capacity of the structure at 250 °C is only 13.1 % lower than that of the room temperature environment, indicating that the temperature softening effect of such composites is not significant. Scanning electron microscope (SEM) and computed tomography (CT) results indicate that the structural damage modes were the crushing of the hole edge fibers and matrix due to the extrusion by the bolts, as well as the interlaminar delamination damage. Temperature effects were taken into account for the composite principal structure and finite element modeling was performed using a combination of Pinho criterion and Cohesive model. Numerical simulations allow accurate prediction of the load-displacement response and damage pattern throughout the damage evolution phase. The high temperature test results and the developed finite element model involved in this study can support the design of new-generation aerospace vehicles.

Aortic stenosis and the evolution of cardiac damage after transcatheter aortic valve replacement

Abstract Aims Cardiac damage staging has been postulated as a prognostic tool in patients undergoing transcatheter aortic valve replacement (TAVR). The aim of our study is to show the echocardiographic and clinical outcome of patients one-year after TAVR. Methods and results Patients undergoing TAVR from 2017 to 2021 were included in a single-centre prospective registry. Transthoracic echocardiography was performed in all patients before TAVR and at one-year. Patients were classified according to a previously published staging model.1 496 patients (mean age 82.1±5.9 years, 53% female) were included. At baseline, Stage 0 included 24.5% of patients, Stage 1 included 42.8%, Stage 2 included 16.5%, and Stage 3 included 16.2% of patients. One-year overall mortality was 17.7% (n=88). Among patients who survived, after one-year of follow-up, the higher the baseline stage of cardiac damage, patients showed larger LVEDV (p= 0.223), LV mass (p= 0.207) and LAVI (p= <0.001); higher E/e’ ratio (p= 0.284) and PASP (p= <0.001). As for LVEF, at one-year; it was significantly lower the higher the baseline stage of cardiac damage (p= 0.005); the same was observed with GLS (p= <0.001) and right ventricle-arterial coupling (p= <0.001), Table 1. Conclusions The higher the stage of initial cardiac damage, the lower the possibility of morphological and functional improvement, despite undergoing TAVR. The use of staging systems and earlier intervention could help improve the prognosis of these patients.

The importance of taste salt sensitivity in the development of kidney damage in patients with high-risked arterial hypertension

Abstract Purpose of the study to evaluate the diagnostic significance of determining taste salt sensitivity in kidney damage development in patients with high-risked arterial hypertension. Material and methods The study included 1021 patients with arterial hypertension (AH), 60% women, 40% men, aged 58.05±7.95 years. All patients underwent the R.Henkin test to determine the threshold of taste sensitivity to table salt in the family polyclinics of Aral Sea region. All patients underwent a complete blood count, a complete urinalysis, biochemical tests, determination of serum creatinine with calculation of glomerular filtration rate, microalbuminuria, urine albumin-to-creatinine ratio and uric acid level. Results Low and medium thresholds of taste salt sensitivity were determined in 149 patients (14.6%, group 1), the average NaCl concentration was 0.15±0.02%. A high threshold of taste salt sensitivity was detected in 872 patients (85.4%, group 2), the average NaCl concentration was 0.64±0.57% (p=0.0001). Patients of the 1st and 2nd groups differed in the level of systolic and diastolic blood pressure (SBP and DBP): 150.8±10.0 mmHg. versus 172.0±16.7 mmHg. p=0.0001 for SBP, 91.4±3.8 mmHg versus 100.7±10.13 mmHg, p=0.0001 for DBP in the 1st and 2nd groups respectively. At the same time, there was a noticeable direct correlation between hemodynamic parameters – SBP / DBP and NaCl concentration in the test for determining the taste sensitivity to table salt threshold (r = 0.646; r = 0.610, respectively). As a result, were detected significantly differences in GFR: 97.22±11.42 versus 70.33±16.56 (p=0.0001); MAU: 58.64±35.45 vs. 215.9±126.65 (p=0.0001); albumin to creatinine ratio: 47.88±42.73 vs. 268.46±261.05 (p=0.0001); uric acid: 227.67±43.75 vs. 337.17±86.52 (p=0.0001), for 1st and 2nd groups respectively. Conclusion A high threshold of taste salt sensitivity, determined by the R.Henken method, is associated with the level of SBP, DBP, markers of kidney damage and the level of uric acid, which increases the diagnostic significance of determining taste salt sensitivity in patients with hypertension.

Oliguria caused by dehydration in combat trauma (case series)

Background. A combat gunshot wound is significantly different from a civilian trauma. It is characterized by the prevalence of penetrating injuries, which increases the volume of blood loss at the pre-hospital stage, and the destruction of large masses of muscle tissue (rhabdomyolysis), which leads to acute kidney injury. Moreover, combat trauma occurs in conditions of chronic background stress as a result of severe emotional and physical strain, uncomfortable weather conditions, and deprivation of sleep, drinking and food. So, such a phenomenon as voluntary dehydration is common among soldiers in combat conditions. In wounded, oliguria is often considered a result of acute kidney injury, but it can also be a symptom of severe dehydration. The purpose of our work was to analyze three clinical cases of oliguria caused by dehydration in wounded with combat trauma to better understand the severity of the condition of such victims and to improve medical aid for them. Materials and methods. The article describes three cases of men aged 35, 50 and 44 years with combat gunshot wounds to the extremities, who were admitted to the tertiary care hospital on the second day after the injury with oliguria (0.18–0.19 ml/kg/hr) and high creatinine (333 to 457 μmol/L). Results. All three patients were conscious, breathing spontaneously, had stable hemodynamics, and moderate anemia after pre-hospital blood transfusions. Focused ultrasound study revealed hyperdynamic left ventricle and small inferior vena cava with complete inspiratory collapse, which suggested hypovolemia. Upon further investigation of the medical history, patients admitted not drinking any liquid for one to two days prior to injury. Tissue hydrophilicity test was conducted which showed severe dehydration in all three cases. Infusion volume was calculated using P.I. Shelestiuk nomogram (modified by O.V. Kravets et al.) and amounted to 60 ml/kg of balanced crystalloid solutions. Upon starting rehydration, diuresis was restored within two hours and amounted to 0.7–2.1 ml/kg/h in all three patients. Creatinine levels normalized in 2–4 days. Patients were transferred to another hospital in a moderate condition in 4–5 days. Conclusions. Oliguria is a frequent complication of combat gunshot injury. Although it is most often associated with acute kidney injury from rhabdomyolysis, it should also be considered that in a combat environment, soldiers’ access to water may be limited and the injury may be accompanied by dehydration. In the cases presented, the differential diagnosis of the causes of oliguria in the wounded made it possible to detect signs of severe dehydration, abstain from the inappropriate use of saluretics, quickly compensate for the fluid deficit, and to avoid the development of kidney damage and the need for renal replacement therapy.

Microstrain partitioning, transformation induced plasticity, and damage evolution of a third generation medium Mn advanced high strength steel

An experimental Medium Mn (med-Mn) steel (0.15C-5.8Mn-1.8Al-0.71Si) with a martensitic starting microstructure, intercritically annealed at 685 °C for 120s, was discovered to have a large true strain at fracture (ɛf = 0.61) while also meeting established (strength x elongation) targets (28,809 MPa%), sustained monotonic work hardening and prolonged Transformation Induced Plasticity (TRIP) kinetics. This was found by varying the intercritical annealing (IA) temperature within a narrow temperature interval in order to isolate its impact on TRIP kinetics and damage development on such med-Mn steel. A comprehensive understanding of the microstructural damage processes leading to fracture is presented using quasi in-situ Scanning Electron Microscope tensile testing as well as X-ray Computed Microtomography. In addition, we precisely evaluated the TRIP kinetics of this steel using a combined Digital Image Correlation (DIC) and synchrotron-sourced High Energy X-ray Diffraction technique. With these methods, we demonstrate that an abundance of voids nucleate during deformation, but their growth can be suppressed by prolonging TRIP over a large strain range. Moreover, novel post-processing techniques to assess DIC acquired data at the microscopic scale have been used to gauge the severity of strain partitioning amongst phases and strain gradient evolution across dissimilar phase interfaces. By comparing it to another 3G TRIP-assisted steel and an ultrafine grained Dual Phase steel. Overall, it has been found that, in addition to carefully moderating TRIP kinetics, the introduction of polygonal ferrite, as is conventional in med-Mn steels, enhances the local forming properties and damage tolerance in 3G TRIP-assisted microstructures.

Investigation of the hygrothermal effects on in-plane failure mechanisms of fine Z-pinned laminates

Hygrothermal effect on the in-plane behavior of fine Z-pinned laminates were studied and the failure mechanisms were explained. Artificial seawater aging experiments were carried out on Z-pinned laminates prepared by ultrasonic vibration equipment. A compression progressive damage numerical model of fine Z-pinned laminates based on moisture-induced interface degradation was proposed to analyze the damage initialization and development of composites. The mechanical results show that the unpinned and Φ0.11 mm Z-pinned laminates have similar in-plane strength retention after 6 months of aging, and the tensile and compressive strengths decrease by 20% and 29%, respectively. EDS analysis confirms that Z-pin provides an additional moisture channel, leading to more elements with high relative atomic mass inside the laminates. It is found through the simulation studies that moisture leads to matrix compression and interlaminar interfacial damage regions to localized areas, weakening the interlayer effect of Z-pins and leading to the decrease of the ultimate bearing capacity of laminates. It denotes that Φ0.11 mm fine Z-pin has the potential to be used in composite marine structures.

Influence of a suboptimal environment and sintering temperature on the mechanical properties of fused filament fabricated copper

Metal injection molding (MIM) processes are generally more cost-effective for the generation of metallic AM components. However, the thermal processing required to remove the polymer and sinter the metal powder is not well understood in terms of resulting mechanical response and damage evolution, especially in ambient atmospheres where contamination is present. This study aims to provide a range of achievable mechanical properties of copper produced using a MIM-based method called fused filament fabrication (FFF) that is post-processed in a nonideal environment. These results showed direct correlations between sintering temperature to multiple aspects of material behavior. In addition, Nondestructive Evaluation (NDE) methods are leveraged to understand the variation in damage evolution that results from the processing, and it is shown that the higher sintering temperatures provided more desirable tensile properties for strength-based applications. Moreover, these results demonstrate a potential to tailor mechanical properties of FFF manufactured copper for a specific application.

An Enhanced Progressive Damage Model for Laminated Fiber-Reinforced Composites Using the 3D Hashin Failure Criterion: A Multi-Level Analysis and Validation.

This paper presents a progressive damage model (PDM) based on the 3D Hashin failure criterion within the ABAQUS/ExplicitTM 2021 framework via a VUMAT subroutine, enhancing the characterization of the mechanical performance and damage evolution in the elastic and softening stages of composite materials via the accurate calculation of damage variables and accommodation of non-monotonic loading conditions. In the subsequent multi-level verification, it is found that the model accurately simulates the primary failure modes at the element level and diminishes the influence of element size, ensuring a reliable behavior representation under non-monotonic loading. At the laminate level, it also accurately forecasts the elastic behavior and damage evolution in open-hole lamina and laminates, demonstrating the final crack band at ultimate failure. This paper also emphasizes the importance of correct characteristic length selection and how to minimize mesh size impact by selecting appropriate values. Compared to ABAQUS's built-in 2D model, the 3D VUMAT subroutine shows superior accuracy and effectiveness, proving its value in characterizing the mechanical behavior and damage mechanisms of fiber-reinforced polymer (FRP) materials. The enhanced 3D PDM accurately characterizes the softening processes in composite materials under simple or complex stress states during monotonic or non-monotonic loading, effectively minimizes the mesh dependency, and reasonably captures failure crack bands, making it suitable for future simulations and resolutions of numerical issues in composite material models under complex, three-dimensional stress states.

Determination of the REV size for heterogeneous rocks with different grain sizes: Deep learning and numerical approaches

Accurate determination of the representative elementary volume (REV) size plays a pivotal role in analysing the mechanical properties and failure processes of heterogeneous rocks in complex engineering environments. In this study, a novel microstructure modelling strategy (NMMS) for determining the REV size is proposed by combining deep learning and an improved phase-field method (PFM). Micro- and macroscale experiments are systematically conducted to determine the real microstructural characteristics and mechanical properties of heterogeneous rocks with different grain sizes. On the basis of this experimental evidence, geometric models of different sizes were reconstructed through deep learning to avoid the limitations of human-based methods, and an improved PFM was used for numerical calculations. These models were then employed to perform numerical tests under uniaxial loading conditions, and the coefficient of variation was introduced to determine the REV size of heterogeneous rocks with different grain sizes. The research findings indicate that the final REV size is the maximum value of the REVs defined by the evaluation properties within an acceptable coefficient of variation. At a criterion of 5% for the coefficient of variation, the REV sizes are 60 mm×60 mm, 70 mm×70 mm, and 90 mm×90 mm for fine-medium-grained (FMG), medium-grained (MG), and coarse-grained (CG) rocks, respectively. Furthermore, the REV determined by the NMMS was applied to investigate the effects of microstructure on macromechanical properties and damage evolution under triaxial loading conditions. The numerical results show that the NMMS can accurately predict the macromechanical properties and microcracking patterns of heterogeneous rocks, especially the intracrystalline cracks in feldspar, the interfacial cracks in gravel, and the “voids” of cracks in biotite. This research can provide some basic references for the optimal choice of the REV size of heterogeneous rocks.

Contemporary issues of the birth trauma

Background. Birth trauma is a group of diseases caused by mechanical factors during childbirth. Birth trauma is an interdisciplinary problem, affecting various fields of medicine, such as obstetrics, pediatrics, child neurology and other sciences. Birth trauma occupies an important place in the structure of perinatal morbidity and mortality. Birth injuries of newborns during vaginal birth occur in 3.6% of cases, during cesarean section — in 1.2%. However, at present, despite a comprehensive study of the problem, the incidence of birth trauma in newborns remains high. Along with obstetric birth trauma, spontaneous birth trauma also occurs — not associated with any obstetric care.Purpose of review. To summarize and analyze the available data on the causes of birth trauma in newborns depending on the type of birth injury.Materials and methods. The review includes published data over the past 10 years regarding the study of the causes of the main types of birth injuries in newborns. The literature search was conducted in Web of Science, Google Scholar, PubMed, and ELibrary databases.Results. The problem of fetal-pelvic disproportion in the genesis of the development of risk factors for maternal-fetal trauma remains relevant. Fetal macrosomia is one of the most significant factors in birth trauma. The most common skull injury in newborns is cephalohematoma. According to the mechanism of occurrence, birth trauma is divided into spontaneous — occurring during physiological childbirth — and obstetric — associated with any obstetric benefits. The degree of configuration of the fetal head plays a significant role in the pathogenesis of birth trauma. Birth trauma is considered as a systemic reaction on the part of the newborn’s body, which leads to a breakdown of compensatory and adaptive mechanisms and the development of critical damage to the central nervous system and is differentiated from birth damage, which includes only local changes.Conclusion. To search for preventive measures aimed at preventing birth injuries in newborns, it is necessary to systematize the groups of causes that influence the increased risk of birth injury. Timely assessment of the pathological configuration of the fetal head is extremely important when deciding on the advisability of using obstetric aids during vaginal operative delivery, since it is an early predictor of the formation of fetal-pelvic disproportion — a significant factor in birth trauma in the newborn. In recent years, taking into account the active study of molecular genetic mechanisms in the genesis of the formation of various pathological conditions, the search for various genetic and epigenetic factors that influence the risk of developing birth traumatic injuries in a newborn against the background of individual susceptibility to the effects of any physical factors during childbirth.

Questioning the Representativeness of Damage Mechanisms in Single-Fiber Composites via In Situ Synchrotron X-Ray Holo-Tomography.

In fiber-reinforced polymer composites, the fiber-matrix interface controls stress transfer mechanisms, thereby affecting mechanical performance. Interfacial properties are often extracted via single-fiber composite tests. In these tests, the load is transferred from the polymer to the fiber through interfacial shear stresses, necessitating the evaluation of interfacial shear properties. To adopt these properties in the design of industrially relevant composites, one must assume that the damage mechanisms in single-fiber composites are representative of those in multi-fiber composites, consisting of highly aligned, unidirectional plies with high fiber volume fractions. That assumption, however, has never been validated. In this paper, the real-time damage development is monitored in single-fiber and multi-fiber composites using in situ X-ray holo-tomography at 150-nm pixel size. The technique enables the first-ever 3D detection of longitudinal interfacial debonding in carbon and glass single-fiber composites. This mechanism is not detected in multi-fiber composite specimens, suggesting that single-fiber composites are intrinsically unrepresentative of realistic composite behavior.

Investigation on fatigue damage of buton rock asphalt mixtures using semi-circular bending (SCB) and digital image correlation (DIC) techniques

The fatigue performance evaluation indices of Buton rock asphalt (BRA) modified asphalt mixture struggles to accurately characterize damage evolution process under repeated loads of the traffic. This study employs digital image correlation (DIC) technology to assess the fatigue behavior of BRA modified asphalt mixture, quantify the correlation between macroscopic response and local deformation, and verify the accuracy of evaluation indices. By capturing strain and displacement fields, the fatigue damage evolution of BRA modified asphalt is analyzed. Based on fracture mechanics theory, BRA’ s improvement of fatigue performance is quantified. Results show that vertical displacement captured by DIC can divide the three stages of fatigue cracking. The global horizontal strain(GExx)and cumulative horizontal strain(CExx) proposed in this study better characterize the nonlinear fatigue damage evolution compared to horizontal strain(Exx). Adding BRA delays crack initiation, reduces propagation rate, and enhances fatigue performance. Strain field evolution was quantitatively analyzed, and horizontal strain density(DE) and global horizontal strain density(GDE) were proposed as fatigue damage indicators. At the same load level, these indicators in BRA modified asphalt mixture, both pre- and post-aging, exceeded those of neat asphalt mixture. These findings provide a novel and accurate approach for evaluating the fatigue damage behavior of BRA modified asphalt mixture, laying the foundation for future performance-based designs.

Multiscale image-based modeling for failure prediction of sheet molding compound composite under uniaxial tension

Carbon fiber reinforced polymer (CFRP) composites are extensively utilized as primary load-bearing components in various engineering applications due to their superior strength-to-weight ratio and excellent mechanical properties. However, their intricate microstructural interactions within composite present a significant challenge for failure analysis of CFRP. Although finite element (FE) simulations have been proven feasible to conduct the failure analysis, the classical FE models are developed based on homogeneous fiber characteristics, ignoring the influence of internal structures on the damage evolution process. This paper presents a multiscale image-based modeling approach to predict the tensile failure procedure of chopped carbon fiber sheet molding compound (SMC) composite. To accurately reconstruct the representative volume element (RVE) model of the SMC composite, synchrotron micro-X-ray computed tomography (μXCT) was adapted to explore the SMC internal microstructure. Then microscale RVE models with different fiber volume fractions were constructed to predict the corresponding microcosmic mechanical properties, which were used as the inputs for mesoscale RVE models to determine the constitutive parameters of fiber chips having varied fiber volume and orientations. Finally, the YOLOv5_Seg algorithm was employed to extract the geometric feature parameters of the fiber chips for mesoscale RVE modeling and then the failure location and sequence under uniaxial tension were predicted. It is found that the final simulated failure behaviors were consistent with the experimental observations, confirming the feasibility of this approach for understanding the failure mechanisms of CFRP composites. Thus, once the internal microstructure is determined using experimental techniques or predicted by simulating the composite manufacturing process, this approach can also be utilized for design optimization and performance evaluation for CFRP composites.

Experimental and numerical investigation on normal strength and high strength RC arches subjected to underwater explosions

As a common structure in engineering, reinforced concrete (RC) arch may be subjected to explosion load in its life cycle. However, there are few studies on the blast resistance of RC arch against underwater explosion. A normal strength reinforced concrete (NSRC) arch and a high strength reinforced concrete (HSRC) arch were designed, and two sets of underwater explosion tests were carried out. Multi-media coupling models of the two RC arches subjected to underwater explosions were established based on the Arbitrary-Lagrangian-Eulerian (ALE) algorithm. The propagation characteristics of shock wave, the acceleration response and damage evolution of the arches were experimentally and numerically investigated. The reliability of the numerical method was verified by comparing the numerical results with the test results. Employing the verified numerical method, the effects of standoff distance and explosive weight on the dynamic response and damage distribution of the NSRC and HSRC arches were further studied. Based on extensive numerical simulations, the prediction formulas for the peak displacement of the given NSRC and HSRC arches due to specific underwater explosions were proposed. The results show that the arch vault and both sides of hance are the most vulnerable to failure when suffering the explosions centrally above the arch. The blast resistance of the HSRC arch is much stronger than that of NSRC arch. The failure modes of RC arches can be summarized as: arch vault cracking, global bending failure, combination of global bending failure and local damage, combination of global bending failure and penetration failure.

Experimental Study on Direct Shear Behavior of New-to-Old Interface for Recycled Aggregate Concrete with Different Replacement Ratios

The large amount of construction waste produced by the construction industry brings severe natural resource consumption and environmental pollution, elevating the awareness of sustainable development. Recycled aggregate concrete, crushed from construction waste, is recognized as an eco-friendly material and the current optimal solution for the environmental problem. The interface shear failure between substrate recycled coarse aggregate concrete (RAC) and overlay natural aggregate concrete becomes vital for structural safety. In order to study the direct shear performance, a total of 19 specimens were designed to carry out the direct shear test with different replacement ratios, interface types and curing ages. The whole process and failure mode were recorded. The relationships between the shear capacity and deformation, ductility, damage evolution, and energy dissipation were evaluated and discussed. The results demonstrate that the RAC component in the interface was the weak line in the shear plane, accelerating the damage evolution. In the early curing stage, the replacement ratio had a slight influence on the shear properties. Increasing the recycled aggregate replacement ratio from 0 to 100% improved the normalized strength ratio by 8.94% and 14.62%, respectively, for curing ages of 3 days and 7 days. A regression equation was proposed to predict the shear strength, accounting for the curing ages. With the increase in the replacement ratio, the ductility and energy dissipation gradually enhanced.

Damage evolution and acoustic emission characteristics of hard rock under high temperature thermal cycles

Damage evolution and acoustic emission characteristics of hard rock under high temperature thermal cycles

Study on Multi-Crack Damage Evolution and Fatigue Life of Corroded Steel Wires Inside In-Service Bridge Suspenders

The parallel steel wires used in arch bridge suspenders experience random corrosion damage on their surfaces during service. Corrosion damage, including micro-cracks, pitting, and a combination of both, leads to significant stress concentration under axial loading, which affects the performance of the steel wires. The change in the stress field caused by surface damage alters the stress intensity factor at the crack tip, and the presence of adjacent crack tips significantly amplifies the stress intensity factor, thereby accelerating crack propagation. The development of small surface damages in the steel wires is difficult to control and observe through experiments. By utilizing finite element methods for simulation, it is possible to intuitively analyze the crack propagation process, the trend of stress changes at the crack tip, and the interaction between damages. Numerical simulation results based on Paris’ law indicate that corrosion pits have a certain impact on the stress intensity factor at the crack tip. The propagation process of coplanar double cracks is highly sensitive to the initial crack size and the distance between adjacent crack tips. When the crack spacing is less than the crack depth, the stress intensity factor at the adjacent crack tips exhibits significant amplification. Based on this phenomenon, the coplanar double-crack system can be simplified to a complete single crack for analysis. By comparing the fatigue life of the double-crack system with that of the equivalent single crack, the effectiveness of the simplification rule has been validated.

Enhancement of pin‐bearing behavior of pultruded FRP profiles by multi‐directional fiber architecture design

AbstractThe low resistance of bolted joints in pultruded unidirectional (UD) fiber‐reinforced polymer (FRP) profiles limits the load grade of truss bridges due to shear damage along UD fibers. To address this issue, this study proposes multi‐directional (MD) fiber architecture in FRP profiles to improve the ultimate bearing strength of bolted joints. The digital image correlation shows that the addition of off‐axis fibers in MD FRP profiles prevents shear failure in the UD FRP profile. As a result, the ultimate bearing strengths of MD FRP profiles are enhanced attributed to “off‐axis fiber tie action”. Micro‐computed tomography shows that fiber damage in MD FRP profiles emerged from outer plies, including fiber breakage in 90° and ±45° fibers and fiber kinking in 0° and ±45° fibers. The off‐axis fibers break due to tension when resisting the bearing load in MD FRP profiles. The fiber kinking indicated strength contribution from 0° to ±45° fibers. The fiber breakage and fiber kinking in each ply are dominant in bearing failure instead of delamination, which increases the bearing strength of the pultruded MD FRP profiles. These findings facilitate controlling damage evolution in the pultruded MD FRP profiles and designing high‐resistance bolted joints.Highlights Multi‐directional fibers improved bearing strengths of FRP profiles by 28.5%–33%. Off‐axis fibers bent under pin‐bearing, forming a tie action until breakage. Fiber breakage and kinking in each ply contributed to the bearing failure. Strain localization and redistribution were observed using DIC.