Repetitive Loading Cycles Research Articles

Response of sand added with various biopolymer contents under repetitive loading and freeze–thaw cycles

Biopolymers have recently been used as ecofriendly materials for soil improvement in terms of stabilization, compressibility, and engineering parameters. The objective of this study is to assess the effect of biopolymer content in sand mixtures during freeze–thaw repetitive loading cycles. The biopolymers were mixed at weight ratios of 0.0, 0.5, 1.0, 2.0, 5.0, and 10 % (BPC 0.0—BPC 10), and the relative density and degree of saturation were fixed at 60 % and 20 %, respectively. The measurement system was located in an ice chamber for freeze–thaw, and 100 cycles of repetitive loads were applied. The test results showed that the deformation decreased from BPC 0.0, to BPC 1.0 owing to the cementation effect produced by the biopolymer chain and coating. However, the deformation increased from BPC 1.0 to BPC 5.0 because high-viscosity solutions might separate the sand particles, causing a density reduction and generating more deformation by compaction. The relative permittivity varied with respect to BPC and freeze–thaw repetitive loading stages that were affected by unfrozen water content, volume contraction, and water consumption during dehydration. The shear wave velocity gradually increased from BPC 2.0 to BPC 10 because the effect of fines in coarse–fine mixtures, rather than the cementation effect. Therefore, the module containing the sensors used in this study can be used to understand the role of biopolymers as reinforcing materials in railway subgrades.

Experimental investigations to assess surface fatigue failure in rolling contact bearing

Rolling element bearings are the most important components in almost all rotating machines. These bearings are often subjected to repetitive load cycles at different operating conditions. Excessive loads, speeds, and improper operating conditions lead to the propagation of defects on their load-bearing surfaces, thereby causing a negative impact on the performance of rotating machines. This paper presents the results of experimental investigations to assess wear propagation in roller bearings using lubricant degradation, vibration, and statistical parameter analysis methods. A roller bearing setup was developed in the laboratory, and the test bearing (NJ 307E) was subjected to fatigue tests over a period of 900 h. The bearing was operated at a speed and radial load of 800 rpm and 1 kN, respectively. The film thickness analysis revealed a transition in lubrication regimes during 600–900 h of operation. Grease structure degradation and oxidation analyses were carried out using scanning electron microscope images and the Fourier transform infrared radiation technique. Further, the vibration signals are extracted from the bearing housing at regular intervals. Using the fast Fourier transform technique, these vibration signals were used to analyze bearing fault frequencies to highlight the faults developed on bearing contact surfaces. The statistical features of vibration signals such as root mean square, kurtosis, and crest factor were used to assess the severity of wear propagated on the bearing contact surfaces. Integrating tribological and vibration parameter analysis techniques provided a reliable assessment of surface fatigue wear propagated on the roller-bearing contact surfaces.

A theoretical model for the prediction of fracture process zone in concrete under fatigue loading: Energy based approach

Characterizing the fracture behaviour of concrete and accurately predicting its service life under fatigue loading poses a significant challenge due to its heterogeneous nature and complex fracture mechanisms. The proposed study focuses on developing an energy based theoretical formulation for predicting the evolution of the fracture process zone throughout repetitive loading cycles. A stiffness degradation approach has been adopted for developing the formulations for the critical energy dissipation and fully developed fracture process zone. Subsequently, the proposed analytical expressions have been calibrated and validated by performing experiments under centre point bending and using available experimental results in the literature. Experiments have been conducted on a centre-point bend beam with varying aggregate size in conjunction with the digital image correlation (DIC) technique to estimate the fracture characteristics. The influence of specimen size and heterogeneity has been discussed in the context of predicting the fracture behaviour, critical dissipated energy, and process zone length of plain concrete beam specimens under fatigue loading. The results indicate that the process zone length and critical energy release rate increase with an increase in specimen size, while the same decreases with an increase in aggregate size.

Sands Subjected to Repetitive Loading Cycles and Associated Granular Degradation

Sands Subjected to Repetitive Loading Cycles and Associated Granular Degradation

An analytical approach for the fracture characterization of concrete under cyclic loading

Many civil engineering infrastructures frequently encounter repetitive loading during their service life. Due to the inherent complexity observed in concrete, like quasi-brittle materials, understanding the fatigue behavior in concrete still poses a challenge. Moreover, the fracture process zone characteristics ahead of the crack tip have been observed to be different in fatigue loading than in the monotonic cases. Therefore, it is crucial to comprehend the energy dissipation associated with the fracture process zone (FPZ) due to repetitive loading. It is well known that energy dissipation due to cyclic loading provides a better understanding of the fracture behavior of concrete. Under repetitive load cycles, concrete members exhibit a two-stage energy dissipation process. Experimentally, it has been observed that the rate of energy dissipation decreases initially with an increase in crack length and subsequently increases. In this work, an attempt has been made to propose an analytical expression to predict energy dissipation as a function of crack length, and the fully developed fracture process zone length under cyclic loading condition.

Full-scale test of Direct-buried Cable in Sand under Repetitive Loading

Direct-buried cable construction can minimize cumbersome processes, thereby decreasing construction time and cost. However, there is no regulation on burial depth that consider the long-term performance of backfilling soil for direct-buried cables. This study examines the mechanical response of direct-buried cables subjected to repetitive loads. This experimental study uses a full-scale chamber to replicate field construction. The stress on the cable, vertical displacement on the surface, and shear wave velocity between loading plate and cable are continuously monitored during 10,000 repetitive loading cycles. A miniature electrical cone is used to indirectly quantify the initial relative compaction. Repetitive loading densifies the soil around the cable, increasing stress on the cable and accumulating vertical strain. The trends are more pronounced with lower initial relative compaction. The shear wave velocity increases during repetitive loading, suggesting a change in the earth pressure coefficient. Applied stress – vertical strain allows the estimation of resilient modulus. These observations will provide a better understanding of the mechanical response of backfilling soil. Additionally, the uniaxial compression test of the underground power cable made for direct burial is conducted to measure the displacement of the cable insulator under the field condition obtained from the full-scale test. Then mechanical stability of the cable is investigated based on the axial displacement of the cable insulator.

A novel seismic energy dissipation device: Laboratory tests, mathematical modeling, and numerical analysis

Seismic energy dissipation devices are used in buildings to dissipate seismic energy in the event of an earthquake. These devices use steel and its yielding properties to dissipate the input seismic energy and protect the building’s structure from damage and failure. There are many types of seismic energy dissipation devices, but all share the same goal of dissipating seismic energy. As part of an ongoing research program, a novel steel seismic energy dissipation device has been proposed. The device is made of a curved diaphragm plate made of mild steel. The diaphragm plate is welded to flanges and transverse stiffeners and can be connected to beam–column joints with a number of bolts. The damper and its geometric variants have been designed and tested in the lab under quasi-static cyclic loading conditions. In the present study, we briefly discuss the experimental program and its main outcomes; however, the main objectives will be mathematical modeling and numerical simulations. The proposed dampers are found to exhibit a stable nonlinear hysteretic behavior with small and large load–deflection loops. This behavior is an indicator of the damper’s capabilities in dissipating significant amounts of input energies with varying intensities. Mathematical modeling of the proposed damper was performed using the Bouc–Wen–Baber–Noori (BWBN) model of hysteresis to simulate the degradation of the device after repetitive loading cycles. The identification of the BWBN model parameters is discussed in detail. Nonlinear finite element buckling analysis was found to be in good agreement with test results of the best performing variant. Interesting results about the shear stress distribution at different buckling stages are presented and discussed in detail.

Poster 254: Mechanical Response of ACL to Submaximal Fatigue Loading

Poster 254: Mechanical Response of ACL to Submaximal Fatigue Loading

Adaptive Equivalent Consumption Minimization Strategy for Off-Road Hydraulic Hybrid Vehicles: A Cycle-to-Cycle Optimization Approach

The energy management strategy is the key factor for hybrid vehicles since it determines how efficiently the engine power is transferred to the wheels. As a local-optimal and implementable strategy, the equivalent consumption minimization strategy is of great research interest. The equivalent factor and the gain coefficient of penalty function are two important parameters in the strategy that need to be determined in advance. It is challenging to choose these parameters to achieve minimum fuel consumption in different on-road driving cycles. For some off-road vehicles, such as wheel loaders, the loading cycle is highly repetitive. This brings a great opportunity to optimize these parameters cycle-to-cycle. In this study, an adaptive equivalent consumption minimization strategy is applied to a series hydraulic hybrid wheel loader. A cycle-to-cycle tuning scheme is developed where the equivalent factor and the gain coefficient of penalty function are optimized through repetitive loading cycles. The potential with parameter optimization in different loading cycles is identified. Results show a fuel-saving with the cycle-to-cycle optimization method of up to 6.36% in a 57 s loading cycle.

OPTIMIZATION OF TRANSFORMERS FOR SOLAR OR BATTERY STORAGE INSTALLATIONS BASED ON A CYCLIC LOADING PATTERN

The popularity of distributed generation forces suppliers to offer more price competitive equipment. This study is aimed at optimization of photovoltaic inverter connected step-up transformers. It also applies to other associated installations, e.g. battery storage. The daily loading patterns in both cases are known. Hence, the effect of this loading would be predicted. The study is for developing a peak load transformer based on the real data collected in a solar farm. The first task is to find out a suitable transformer rating that is equal to average “dissipated” power. The peak generation and the peak loading only occur for a short time during each day. Hence, the equipment does not have to be designed to this maximum capability of the solar panels and the inverter. The transformer rating could be reduced, to reduce the cost of the equipment while keeping the performance and reliability at the highest level. The second aim is to find optimal transformer design, including the most suitable insulation system for handling the expected cyclic loading. The analysed insulation systems included Kraft papers, thermally upgraded papers and the thermally upgraded cellulose paper enhanced with aramid. That last solution appears to be the best option for transformers experiencing repetitive loading cycles.

Multifunctional behavior of composite beams incorporating hybridized carbon-based materials under cyclic loadings

The investigation was performed on the cyclic self-sensing behavior of reinforced composite beams produced with carbon fiber (CF) and carbon black (CB) in a hybridized form. Prior to the investigation, CFs and CBs were individually used in small-scale specimens at different ratios. The electrical properties were tailored by binary using of CFs and CBs for the improved self-sensing functionality. After evaluation of electrical and mechanical properties, self-sensing reinforced composite beams were produced with a span/effective depth ratio of 2.2. Repetitive loading and unloading cycles within elastic and plastic range were separately evaluated and applied for the developed composite beams. Beams were tested up to 30% and 70% of their ultimate flexural strength for the cyclic loadings within elastic and plastic range, respectively. Engineering properties and self-sensing assessments were simultaneously performed. Experimental findings revealed that developed composite beams provided a reversible piezoresistive behavior under plastic regime although it was partially possible under the elastic regime. Only beams coupled with hybrid carbon-based materials were able to repetitively self-sense damages between %30 and %70 of the total applied load. Carbon-based materials made a slight contribution to the engineering properties of beams as also validated by finite element analysis.

What does 'toughness' look like? An examination of the breakdown of young and mature leaves under cyclical loading.

The material property of leaf toughness is considered the crucial mechanical challenge facing folivorous primates. Mature leaves have higher recorded toughness values than young leaves on average, leading to many assumptions about the patterning of food breakdown that follow a tough/not-tough dichotomy. We tested three hypotheses about how leaves break down under repetitive loading cycles, predicting that mature leaves (i) experience more force during simulated occlusal loads, (ii) more effectively resist fragmentation into small pieces, and (iii) show a more gradual decline in resistance over consecutive cycles than young leaves. Under displacement control using a mechanical testing system, we subjected young and mature leaves to 20 cycles of axial loading using interlocking steel wedges, then collected and quantified the size of the leaf fragments. While we found that mature leaves experienced more overall force than young leaves (p < 0.001), they also shattered into smaller pieces (p = 0.004) and showed a steeper decline in their resistance to the cycles over the course of a test (p < 0.01). These results suggest that putatively 'tougher' foods (i.e. mature versus young leaves) do not necessarily resist fragmentation as commonly assumed. The current tough/not-tough paradigm of primate foods may not accurately reflect how leaves break down during masticatory behaviour.

Torsional Resistance of WaveOne Gold and Reciproc Blue according to the Loading Methods

IntroductionThis study aimed to compare the torsional resistances and fracture modes of WaveOne Gold (Dentsply Sirona, Ballaigues, Switzerland) and Reciproc Blue (VDW, Munich, Germany) using the repetitive torsional loading (RTL) method and the conventional single-rotation (STL) method. MethodsA 3-mm file tip was fixed with a brass plate, and a torsional load was applied using a custom device. In the RTL method, the file was driven counterclockwise at 50 rpm until it achieved the preset torque of 0.5 Ncm; thereafter, it was returned to its original position. This recovery of the file to its original position was defined as 1 torsional loading cycle; the number of repetitive load cycles until fracture was counted. In the STL method, the files were rotated at a constant rate of 2 rpm in a counterclockwise direction until file fracture. The fragments fractured by the 2 methods were compared under a scanning electron microscope to examine the topographic features of the fractured surfaces and longitudinal aspects. ResultsWith the RTL method, Reciproc Blue showed a higher number of repetitive load cycles until fracture than WaveOne Gold (P < .05). With the STL method, Reciproc Blue also had a higher ultimate strength than WaveOne Gold (P < .05). Scanning electron microscopic findings of the fractured specimens from the 2 test methods showed different features of torsional failure. ConclusionsWithin the study limitations, both the RTL and STL methods conferred similar torsional resistance. Therefore, the clinically relevant RTL method with repetitive and reciprocation motion can be used for testing torsional resistance.

Static and cyclic characterization of fouled railroad sub-ballast layer behaviour

This paper investigates the static and cyclic characteristics of a fouled sub-ballast material using static and cyclic triaxial tests. Static triaxial tests were conducted first to determine the peak strength, which was used as the applied stress in the cyclic tests. Moreover, the results of the displacement-controlled static triaxial test were used to assess the shear stiffness and strength during the cyclic stress-controlled loading cycles. Isotropically consolidated drained (CD) compression cyclic triaxial tests were conducted to simulate the long-term response of fouled railway substructure under progressive repetitive loading and unloading cycles. The accumulated plastic strains of the fouled railroad sub-ballast were determined under cyclic loading and unloading conditions. The obtained results indicated that the soil plasticity and effective confining pressure, and relative density are not the only important factors in shaping the damping curves but also the loading rate, and particle size. Both parameters play a major role in determining the behaviour of fine contaminated sub-ballast. The railway operational speed limits were deduced from the stress-strain behaviour of the fouled sub-ballast interlayer zone. It is recommended that the maximum speed of trains in fouled railroad segments be limited to a maximum of 32 km/h. The developed guidelines are aimed to prolong the service lifespan of the fouled track segments, while maintaining safety standards to avoid train derailments, track deterioration, and high maintenance costs.

Crushing and embedment of proppant packs under cyclic loading: An insight to enhanced unconventional oil/gas recovery

Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects. These persistent production drops due to the non-linear responses of proppants under reservoir conditions put the future utilization of such advanced stimulation techniques in unconventional energy extraction in doubt. The aim of this study is to address these issues by conducting a comprehensive experimental approach. According to the results, whatever the type of proppant, all proppant packs tend to undergo significant plastic deformation under the first loading cycle. Moreover, the utilization of ceramic proppants (which retain proppant pack porosity up to 75%), larger proppant sizes (which retain proppant pack porosity up to 15.2%) and higher proppant concentrations (which retain proppant pack porosity up to 29.5%) in the fracturing stimulations with higher in-situ stresses are recommended to de-escalate the critical consequences of crushing associated issues. Similarly, the selection of resin-coated proppants over ceramic and sand proppants may benefit in terms of obtaining reduced proppant embedment. In addition, selection of smaller proppant sizes and higher proppant concentrations are suggested for stimulation projects at depth with sedimentary formations and lower in-situ stresses where proppant embedment predominates. Furthermore, correlation between proppant embedment with repetitive loading cycles was studied. Importantly, microstructural analysis of the proppant-embedded siltstone rock samples revealed that the initiation of secondary induced fractures. Finally, the findings of this study can greatly contribute to accurately select optimum proppant properties (proppant type, size and concentration) depending on the oil/gas reservoir characteristics to minimize proppant crushing and embedment effects.

Microscopic Multiple Fatigue Crack Simulation and Macroscopic Damage Evolution of Concrete Beam

Microcracks in concrete can coalesce into larger cracks that further propagate under repetitive load cycles. Complex process of crack formation and growth are essentially involved in the failure mechanism of concrete. Understanding the crack formation and propagation is one of the core issues in fatigue damage evaluation of concrete materials and components. In this regard, a numerical model was formulated to simulate the thorough failure process, ranging from microcracks growth, crack coalescence, macrocrack formation and propagation, to the final rupture. This model is applied to simulate the fatigue rupture of three-point bending concrete beams at different stress levels. Numerical results are qualitatively consistent with the experimental observations published in literature. Furthermore, in the framework of damage mechanics, one damage variable is defined to reflect stiffness reduction caused by fatigue loading. S-N curve is subsequently computed and the macroscopic damage evolution of concrete beams are achieved. By employing the combined approaches of fracture mechanics and damage mechanics, made possible is the damage evolution of concrete beam as well as the microscopic multiple fatigue crack simulation. The proposed approach has the potential to be applied to the fatigue life assessment of materials and components at various scales in engineering practice.

Biomechanical comparison of three tension band wiring techniques for transverse fracture of patella: Kirschner wires, cannulated screws, and ring pins.

The purpose of this study is to compare biomechanical characteristics of tension band wiring using Kirschner wires (TBWKW), cannulated screws (TBWCS), and ring pins (TBWRP) for transverse fracture of the patella. A total of 48 polyurethane synthetic patellae were biomechanically tested. All patellae were osteotomized to create a transverse fracture. Each TBWKW, TBWCS, and TBWRP fixed 16 broken patellae. A specially designed fixation board simulated a knee with 90° flexion. Ten static tests and six dynamic tests were performed on each method. The static test is measuring maximum strength (N) during traction until breakage of the fixation. The dynamic test consisted of measuring the fracture gap (mm) after 10,000 repetitive loading cycles between 100 N and 300 N that simulated actual daily activity. A gap of 2 mm or more was defined as a failure in both tests. The failure load was 438.6 ± 138.6 N, 422.2 ± 72.7 N, and 1106.8 ± 230.3 N for TBWKW, TBWRP, and TBWCS, respectively. TBWCS showed a statistically significant difference compared to TBWKW and TBWRP in the static test (p < 0.001). All the groups had no failure in the dynamic test. The mean fracture gap after completion of the dynamic test was 0.3267 ± 0.3395 mm, 0.2938 ± 0.2165 mm, and 0.0360 ± 0.0570 mm for TBWKW, TBWRP, and TBWCS, respectively (p = 0.044). The mean values in the dynamic test showed no statistical difference. There was a significant difference between TBWRP and TBWCS (p = 0.009), but others showed no difference with statistical significance. All three methods have sufficient stability at a daily activity. TBWCS showed a better failure load compared with TBWKW and TBWRP. TBWRP showed compatible mechanical characteristics with traditional tension band wiring. TBWRP could be an alternative method for TBWKW.

Elastic recovery of polymeric braided stents under cyclic loading: Preliminary assessment

Over the last decades, stents have been largely used to treat vascular diseases such as coronary artery or peripheral vessel stenosis. Among the solutions which are commercially available to treat vascular stenosis, metallic stents represent the gold standard. However, issues such as restenosis, corrosion and fractures have been reported with these devices and are especially due to the material which is used. Braided polymeric stents could present an alternative to replace metallic stents especially in peripheral vessels where flexibility is required. Among polymeric materials, polyethylene terephthalate (PET), could be a good candidate as its biocompatibility has already been widely proven especially in the field of cardiovascular applications. Moreover, braided devices have been already used for the stenting of peripheral zones, providing locally outstanding flexibility due to the discontinuity of these structures. The goal of this work was to evaluate the radial strength and the recovery performances of polymeric braided stents made from PET monofilaments. In particular, the behavior of these stents under repeated cyclic radial compression loading was assessed and compared to results obtained with a metallic braided stent of same diameter. Results show that polymeric braided stents provide 100% elastic recovery after 20% diameter compression over 2000 repetitive loading cycles. However, radial strength goes slightly down with cycling, which points out that friction occurs in the braid. It comes out from the study that a braided polymer stent shows suitable mechanical behavior compared to a metallic stent over cyclic loading up to 2000 cycles. Moreover, it is shown that the mechanical behavior of these stents depend highly on the braid angle.

Sand response to a large number of loading cycles under zero-lateral-strain conditions: evolution of void ratio and small-strain stiffness

Geotechnical structures often experience a large number of repetitive loading cycles. This research examines the quasi-static mechanical response of sands subjected to repetitive loads under zero-lateral-strain boundary conditions. The experimental study uses an automatic repetitive loading frame operated with pneumatic pistons. Both vertical deformation and shear wave velocity are continuously monitored during 10 000 repetitive loading cycles. The void ratio evolves towards the terminal void ratio eTas the number of load cycles increases. The terminal void ratio eTis a function of the initial void ratio e0and the stress amplitude ratio Δσ/σ0. The number of cycles N* required to reach half of the final volume contraction ranges from N*→1 for densely packed sands (e0→emin) to N→103for loosely packed sands (e0→emax). As the soil approaches terminal density at a large number of cycles, peak-to-peak strains are dominated by elastic deformations, and the minute plastic strains that remain in every cycle reflect local and sequential contact events. The shear wave velocity increases during cyclic loading with data suggesting a gradual increase in the coefficient of earth pressure K0during repetitive loading. Changes in shear wave velocity track the evolution of the constrained modulus M; in fact, the constrained modulus can be estimated from the shear wave velocity to compute soil deformation in a given cycle. A simple procedure is suggested to estimate the potential settlement a layer may experience when subjected to repetitive mechanical loads.

Determining weight-bearing tissue condition using peak reactive hyperemia response trend and ultrasonographic features: Implications for pressure ulcer prevention.

Frequent repositioning is important to prevent pressure ulcer (PU) development, by relieving pressure and recovering damages on skin areas induced by repetitive loading. Although repositioning is the gold standard to prevent PU, there is currently no strategy for determining tissue condition under preventive approaches. In this study, the peak reactive hyperemia (RH) trends and ultrasonographic (US) features are compared with the tissue condition under histopathological examination to determine the potential use of these features in determining the tissue condition noninvasively. Twenty-one male Sprague-Dawley rats (seven per group), with body weight of 385-485 g, were categorized into three groups and subjected to different recovery times, each with three repetitive loading cycles at skin tissues above of right trochanter area. The first, second, and third groups were subjected to short (3 minutes), moderate (10 minutes), and prolonged (40 minutes) recovery, respectively, while applying fixed loading time and pressure (10 minutes and 50 mmHg, respectively), to provide different degree of recovery and tissue conditions (tissue damage and tissue recovery). Peak RH was measured in the three cycles to determine RH trend (increasing, decreasing, and inconsistent). All rat tissues were evaluated using ultrasound at pre- and post-experiment and rated by two raters to categorize the severity of tissue changes (no, mild, moderate, and severe). The tissue condition was also evaluated using histopathological examination to distinguish between normal and abnormal tissues. Most of the samples with increasing RH trend is related to abnormal tissue (71%); while inconsistent RH trends is more related to normal tissue (82%). There is no relationship between the tissue conditions evaluated under ultrasonographic and histopathological examination. Peak RH trend over repetitive loading may serve as a new feature for determining the tissue condition that leading to pressure ulcer.