Dynamic Cyclic Loading Research Articles

Degradation Analysis of a Commercial SOFC System

Solid Oxide Fuel Cell (SOFC) technology offers several advantages such as fuel flexibility, high efficiency, and zero criteria pollutant emissions. SOFC systems have the potential to be cheaper and provide more reliable and cleaner electrical load-following characteristics compared with other technologies by dynamic operation and control. Cost and durability are major challenges associated with current SOFC technology. Durability of Solid Oxide Fuel Cell (SOFC) technology is a key aspect for its commercialization and long-lasting deployment in different applications. Dynamic operating conditions have considerable effects on the long-term performance and durability of SOFC systems.In this study, we evaluate the performance and degradation of a 1.5 kW (AC) commercial system under steady state and dynamic load cycling conditions for over 6000 hours. We monitored and evaluated the initial and degraded performance characteristics of the SOFC stack, while testing under constant 1.6 kW load, 85% fuel utilization, and at 760°C stack temperature for 4000 hours and under dynamic cycling load for more than 2000 hours. We conducted degradation tests based upon two load cycling profiles: i) accelerated daily cycles with load changing from 0.5 kW to 1.6 kW, with stack temperatures ranging between 720°C and 760°C, and fuel utilization between 55% and 85% for 42 cycles (~1000 hours), and ii) weekly cycling test with load changing from 0.5 kW to 1.6 kW with lower slope for 10 cycles (1600 hours). A machine learning model based upon experimental data is developed to correlate the degradation rate of the system to different features of dynamic profiles to be used in the prediction of degradation rate for a wide range of dynamic load profiles.Test results show that the degradation rate is 0.025% (2mV) per 1000 hours of operation under steady state operating conditions. As the system degrades under steady state conditions, fuel consumption increases 0.3% while the efficiency drops 0.3% per 1000 hours of operation. We observe that at beginning of life and during the first 1000 hours of operation, the degradation rate is roughly twice as high as that achieved under steady state operation (i.e., 4.8mV). Results show that the system also degrades twice as fast when forced to meet daily dynamic cycling loads. The degradation rate observed under highly dynamic daily load cycling conditions is 0.58% (4.7mV) per 1000 hours of operation over 42 daily cycles.

Recent Achievement of Degradation Analyses in Japanese National Project: High Efficiency and Dynamic Operation Effects on the Durability of SOFC Stacks

In this report, recent achievements of the Japanese national projects (NEDO projects) are presented, especially on the rapid evaluation methods for cell-stack degradation (2018-2019) and the “Development of advanced evaluation and analysis technologies for the durability of Solid Oxide Fuel Cells stacks (2020-)”. The durability of practical cell-stacks was examined under high fuel utilization (Uf) conditions (over 80%) and dynamic load cycling operations at different kinds of cell-stack geometry: flat-tubular and planer. All stacks showed relatively stable performance even in high Uf and load cycling. The degradation mechanism of Ni-YSZ anode cermet was especially examined in terms of Ni migration and morphology change at the Ni/oxide contact. It was found that the Ni migration and morphological change were small in the practical cell-stacks although a significant change was reported in several tests. The discussion on the relationship between performance degradation and morphological change was made under high water vapor conditions.

The influence of alternating cyclic dynamic loads with different low frequencies on the bio-corrosion behaviors of AZ31B magnesium alloy in vitro

The real physiological environment of human body is complicated with different degrees and forms of dynamic loads applied to implanted medical devices due to the daily activities of the patients, which would have impacts on the degradation behaviors of magnesium alloy implants. In this work, the bio-corrosion behaviors of AZ31B magnesium alloy under alternating cyclic dynamic loads with different low frequencies (0.1–2.5 Hz) were specially investigated. It was found that the bio-degradation performances under external dynamic stressed conditions were much severer than those under unstressed conditions and static loads. The corrosion rates were generally accelerated as the rise of cyclic frequency. Hereby a numerical model for the degradation process of Mg alloy was established. The corrosion current density icorr of Mg alloy and the applied loading frequency f matches a linear relationship of ln icorr∝ f, which is the result of interactions between the cyclic alternating load and corrosive environment. This work could provide a theoretical reference and an experimental basis for further researches on the biodegradation behaviors of biomedical materials under dynamic conditions.

Occlusal Thickness and Cement-Type Effects on Fracture Resistance of Implant-Supported Posterior Monolithic Zirconia Crowns.

To evaluate the factors that could influence the fracture resistance of implant-supported posterior monolithic zirconia crowns. Sixty zirconia molar crowns with three different occlusal thicknesses of 0.5, 1.0, and 1.5 mm (20 samples per group) were prepared for implant abutments using a CAD/CAM system. In each group, 10 crowns were luted on the abutment with resin cement (Panavia F), and the other 10 crowns were luted with resin-modified glass-ionomer cement (Ketac Cem Plus). Dynamic loading (1.2 × 106 cycles; 70 N) and thermal cycling were applied to the samples using a chewing simulator before evaluating their fracture resistance with a universal testing machine and examining their fracture type using a stereomicroscope. One-way analysis of variance (ANOVA), the Duncan test, and two-way ANOVA were used for data evaluation (α = .05). The occlusal thickness (P < .001) and cement type (P < .01) affected the fracture load of the monolithic zirconia crowns. The highest fracture resistance was found in 1.5-mm-thick crowns luted with resin cement (4,212 ± 501 N), and the lowest fracture resistance was found in 0.5-mm and 1-mmthick crowns luted with resin-modified glass-ionomer cement (1,198 ± 116 N and 1,197 ± 66 N). A significant difference was not found in the mean maximum fracture load between the 1.5-mm-thick crowns cemented with resin cement and glass-ionomer resin cement. Both the occlusal thickness and cement type remarkably affected the fracture resistance of the crowns, but occlusal thickness was more significant. Implant-supported posterior zirconia crowns can withstand physiologic occlusal forces even with a thickness as low as 0.5 mm. Resin luting cement is recommended for implant-supported posterior zirconia crowns with reduced occlusal thickness.

Assessment of Biomechanical Behavior of Endodontically Treated Premolar Teeth Restored with Novel Endocrown System.

Despite the increased popularity of endocrowns, there is no clear consensus considering their effectiveness to restore severely-destructed endodontically treated premolars. This study aimed to assess the biomechanical behavior of endodontically treated maxillary first premolars restored with a novel endocrown system compared to the conventional one. Twenty sound human maxillary first premolars were collected. After endodontic treatment, they were divided into 2 groups (n=10) according to the system used for endocrown fabrication. Group C (Control): conventional monolithic IPS e.max CAD endocrowns. Group P: novel bi-layered endocrowns (Pekkton ivory coping veneered with cemented IPS e.max CAD). All specimens were subjected to 10000 thermal cycles followed by 240000 dynamic load cycles. Surviving specimens were subjected to fracture resistance test followed by qualitative analysis using Stereomicroscopy and Scanning Electron Microscopy. A significantly higher load was observed for Group P (1831.37 ± 240.69 N) than Group C (1433.47 ± 174.39 N) (p ⟨ 0.001). A statistically significant difference was observed considering the failure mode (p = 0.036), with more favorable fractures detected with Group P. The tested novel endocrown system improved the biomechanical behavior of the tooth/ restoration complex in the restored endodontically treated maxillary first premolars. The tested novel endocrown system with a PEKK coping veneered with cemented IPS e.max CAD can be considered a promising option for restoration of severely-destructed endodontically treated premolar teeth. It can be considered as a conservative alternative option to the conventional treatment modalities.

Double plating is associated with higher fixation strength than single plating in osteoporotic fractures of the scapular spine: a biomechanical study

IntroductionThe number of atraumatic stress fractures of the scapular spine associated with reverse shoulder arthroplasty is increasing. At present, there is no consensus regarding the optimal treatment strategy. Due to the already weakened bone, fractures of the scapular spine require a high fixation stability. Higher fixation strength may be achieved by double plating. The aim of this study was to evaluate the biomechanical principles of double plating in comparison to single plating for scapular spine fractures.MethodsIn this study, eight pairs (n = 16) of human shoulders were randomised pairwise into two groups. After an osteotomy at the level of the spinoglenoid notch, one side of each pair received fracture fixation with a single 3.5 LCP (Locking Compression Plate) plate. The contralateral scapular spine was fixed with a 3.5 LCP and an additional 2.7 LCP plate in 90–90 configuration.The biomechanical test protocol consisted of 700 cycles of dynamic loading and a load-to-failure test with a servohydraulic testing machine. Failure was defined as macroscopic catastrophic failure (screw cut-out, plate breakage). The focus was set on the results of specimens with osteoporotic bone quality.ResultsIn specimens with an osteoporotic bone mineral density (BMD; n = 12), the mean failure load was significantly higher for the double plate group compared to single plating (471 N vs. 328 N; p = 0.029). Analysis of all specimens (n = 16) including four specimens without osteoporotic BMD revealed no significant differences regarding stiffness and failure load (p > 0.05).ConclusionDouble plating may provide higher fixation strength in osteoporotic bone in comparison to a single plate alone. This finding is of particular relevance for fixation of scapular spine fractures following reverse shoulder arthroplasty.Level of evidenceControlled laboratory study.

Performance of Polypropylene Fiber-Reinforced Solidified Soil

Urgent repair and construction of airstrips is a research hotspot in global airport engineering. Selecting the proper structural materials is a key component of the airstrip repair process. First, with unconfined compressive strength and splitting tensile strength, the fiber length and content of polypropylene (PP) fiber-reinforced solidified soil were optimized. Then, using a scanning electron microscope, the reinforcing mechanism of PP fiber on soil and the influence mechanism of fiber parameters on fiber-reinforced soil were discussed and analyzed. Lastly, a full-scale test section was paved, on which static and dynamic loading tests were performed to verify the carrying capacity and deformation characteristics of the full-scale test section. The above research provides a theoretical foundation and data support for the urgent repair and construction of airstrip. Results indicate that PP fiber with length of 12 mm and fiber content of 0.3% has optimal performance and economic cost. The reinforcing mechanism of fiber-reinforced soil can be summarized to be the effect of a one-dimensional lacing wire and the effect of a three-dimensional network structure. Fibers show two failure modes of pull-out and tensile failure. After 20000 dynamic loading cycles, the stress at the bottom of each structural section varies less, the graded plastic deformation is stable, and the cumulative plastic deformations of the fiber-reinforced soil base, solidified soil base, and cemented soil base pavement structures are 0.83 mm, 0.93 mm, and 1.2 mm, respectively. Pavement structure composed of fiber-reinforced solidified soil can meet the load capacity requirements for use in airstrips under the characteristics of time-sensitive application.

Electrospinning of small diameter vascular grafts with preferential fiber directions and comparison of their mechanical behavior with native rat aortas

Conventional electrospun small diameter vascular grafts have a random fiber orientation. In order to achieve mechanical characteristics similar to a native blood vessel, a controllable fiber orientation is of interest. In this study the electrospinning jet was directly controlled by means of an auxiliary, changeable electrostatic field, so that the fibers could be deposited in adjustable orientations. Prostheses with circumferentially, axially, fenestrated and randomly aligned fibers were electrospun on Ø2mm mandrels out of a thermoplastic polyurethane (PUR) and a polylactid acid (PLLA). The impact of the materials and the various preferential fiber orientations on the resulting biomechanics was investigated and compared with that of the native rat aorta in quasistatic and dynamic hoop tensile tests. The test protocol included 3000 dynamic loading cycles in the physiological blood pressure range and ended with a quasistatic tensile test. Any orientation of the fibers in a particular direction resulted in a significant reduction in scaffold porosity for both materials. The standard randomly oriented PUR grafts showed the highest compliance of 29.7 ± 5.5 [%/100 mmHg] and were thus closest to the compliance of the rat aortas, which was 37.2 ± 6.5 [%/100 mmHg]. The maximum tensile force was increased at least 6 times compared to randomly spun grafts by orienting the fibers in the circumferential direction. During the 3000 loading cycles, creeping of the native rat aorta was below 1% whereas the electrospun grafts showed creeping up to 2.4 ± 1.2%. Although the preferred fiber orientations were only partially visible in the scanning electron micrographs, the mechanical effects were evident. The investigations suggest a multi-layer wall structure of the vascular prosthesis, since none of the preferred fiber directions and the materials used could imitate the typical j-shaped mechanical characteristics of the rat aorta.

Morphological characterisation of 2D packing with bi-disperse particles

The morphological structure of granular materials can dominate their mechanical, hydraulic, electrical, and thermal properties; thus, the formation of order and disorder arrangement of particles is the key characteristic to describe such micro-structures. During the packing procedure, external energy input and perturbations, such as dynamic cyclic load, and the particle size distribution were mentioned by many previous works to be significant in controlling the structure. This study explores order to disorder transition within 2D binary granular assemblies under vibration. A numerical packing method combining particle size growth and dynamic vibration is implemented and verified against experiments to achieve desired packing structure. The Bond orientation order number and pair distribution function are used as indices for characterising the morphological structure. Our packing simulation results show a combination of appropriate vibration and a proper particle size growth rate can facilitate the formation of granular crystallisation. Additionally, for binary packing, the size ratio, and the number fraction of small particles can play a critical role in determining the morphological transformation.

Dynamic current cycles effect on the degradation characteristic of a H2/O2 proton exchange membrane fuel cell

The durability and reliability of H2/O2 proton exchange membrane fuel cell (PEMFC) is a key factor that prevents its wide application in the civil field. PEMFC inevitably experience different dynamic loading cycles according to different power switching requirements during practical operation. To explore the degradation behavior under different dynamic cycles, a single H2/O2 PEMFC with 50 cm2 active area was operated under the circulating current density from 100 mAcm−2 to 600 mAcm−2, 100 mAcm−2 to 800 mAcm−2, and 100 mAcm−2 to 1000 mAcm−2, respectively. The change of polarization curve, performance degradation at different current density, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) were characterized to investigate the performance degradation over dynamic current cycles. Besides, the Scanning Electron Microscopy (SEM) was used to evaluate the degradation of catalyst layer. The results indicated that the degradation rate of the fuel cell performance increased corresponding to the cycle number, at 1200 mA/cm2, it with a total performance degradation rate of 11.83% after 2000 dynamic loading cycles with the circulating current density from 100 mAcm−2 to 600 mAcm−2. The degradation of electrochemical performance such as CV and EIS was consistent with that of fuel cell performance. The degradation rate is accelerated with the increase of loading cycle number and load step amplitude. What’ more, EIS provides additional sensitivity to differentiate catalyst layer degradation within PEMFC. Moreover, the degradation of the catalyst layer became much more severe under a larger load step amplitude.

Experimental investigation of linear damping characteristics on granite and red sandstone under dynamic cyclic loading

Damping is a significant dynamic characteristic used to describe rock vibration failures and plays an important role in various seismic engineering applications, specifically for evaluating stability of rock masses under forced vibration loading. In this paper, cyclic loading tests were carried out on sandstone and granite samples to study their damping characteristics. The effect of the selected influential indicators (stress level, strain amplitude and loading frequency) on the damping ratio and damping coefficient was studied. The damping parameters of sandstone and granite were calculated and the variability in the damping parameters as a function of stress level, frequency and strain amplitude were determined. The linear relationship between damping ratio, damping coefficient and strain amplitude was investigated. The results suggest that the relationship between the damping parameters and the strain amplitude could be expressed as a linear function. The influential indicators to the damping parameter of granite were sorted as follows: stress level > strain amplitude > frequency. The influential indicators of sandstone were sorted as follows: strain amplitude > stress level > frequency. Under a fixed-amplitude stress path, the damping ratio of granite was approximately 80% that of the sandstone and the damping coefficient is approximately 200% of that of the sandstone.

Smart Cementitious Composites for Road Traffic Monitoring and Weighing in Motion

The addition of electrically conductive materials at micro scale, such as carbon fibres (CF) or steel fibres (SF), to conventional cementitious materials makes piezo-resistive behaviours possible in terms of changes in electrical resistivity due to applied stresses. Smart cementitious composites (SCCs) may thus be able to detect traffic density and sense weight in motion thanks to such piezo-resistive property. Three types of cement-based sensors, with CF, SF, or a hybrid of CF and SF, were experimentally evaluated by applying quasi-static and dynamic load cycles after seven days of curing in different load directions reflecting the electrodes and different circuit type connections of the specimens. The performance of each type of sensor was assessed based on measuring the changes in electrical resistivity (ER) under compressive and flexure stresses, with test results revealing that the use of CF in these composites was the best choice because this generated more sensitivity to applied loads in terms of the change in ER compared with other types. These results were achieved when the applied load was parallel to the electrode direction. The findings also indicated arrangement of specimens as an electric series circuit type was the best setup configuration for traffic monitoring and weight in motion measurement.

Seismic barriers filled with granular metamaterials: Mathematical models for granular metamaterials

The problem of seismic protection from the main types of surface acoustic waves and shear–pressure (SP) evanescent waves emanating from vicinity of an epicenter of an earthquake is discussed. Herein, SP waves represent a kind of the evanescent waves arising at critical angles of incident of bulk shear waves. The proposed seismic protection method utilizes vertical trenches (vertical barriers) filled with the specially constructed granular metamaterials. Some of nonlinear hyperelastic models along with nonlinear and inelastic models are analyzed for applications using granular metamaterials in case of cyclic dynamic loadings that correspond to arrival of the large intensity surface acoustic and evanescent waves. The main attention is paid to arrival of the large intensity Rayleigh, Rayleigh–Lamb and SP waves, as the most frequent waves and the most dangerous waves for engineering structures. Some of the new constitutive equations for metamaterials exhibiting different elastic moduli at tension and compression phases are proposed and discussed.

Performance prediction of fuel cells using long short‐term memory recurrent neural network

Performance prediction of proton-exchange membrane fuel cell (PEMFC) under dynamic conditions, especially for vehicle applications, is increasingly become the focus of attention. This article proposes a performance prediction method of PEMFC using long short-term memory (LSTM) recurrent neural network (RNN). In this article, polarization curve (current-voltage curve) and voltage degradation curve (current-time curve) are adopted as the main performance indexes of PEMFC. Both polarization curve prediction and performance degradation prediction of PEMFC can be effectively implemented based on the LSTM method. To investigate the voltage losses law of experimental and predicted results, the paper introduces an empirical equation of polarization curve. The perfect match between the experimental and predicted polarization losses of PEMFC can further validate the prediction performance of LSTM method. The proposed prediction method is validated by the PEMFC polarization curve data obtained from the designed aging experiment of a 4 kW stack operated under dynamic loading cycling situation during 600 hours. Then, LSTM network is compared with traditional RNN and back-propagation neural network (BPNN) to prove its superiority. The minimum values of root-mean-square error (RMSE) and the mean absolute percentage error (MAPE) of LSTM network with different training data are 0.0088 and 0.0101, respectively. All the coefficient of determination (R2) of LSTM model with different training data is over 0.95, which is close to 1.0. The prediction accuracy of LSTM network is higher than that of two other networks. The result indicates that LSTM network outperforms two other networks in PEMFC performance prediction. Hence, the prediction method based on LSTM network is very suitable for PEMFC performance prediction.

Experimental and numerical study on viscously-damped outriggers with amplifying devices

A novel concept, labeled as amplified viscously-damped outrigger (AVDO) is proposed in this paper. It combines the viscously-damped outrigger (VDO) and steel amplifying devices to make the damper achieve higher energy dissipation capacity. Two newly-proposed configurations of AVDO were fabricated and compared with the conventional VDO by the dynamic cyclic loading test. The test results showed that AVDO can effectively amplify the deformation and energy dissipation of the damper. The change rule of the amplification factor and the difference between the experimental value and the theoretical value was analyzed, which highlighted that the deformation of components and the clearance in the pin joint had a great influence on the amplification of AVDO. Furthermore, a newly-developed model of joint clearance was used in the FE analysis of AVDO and validated with the experimental results. The stiffness of amplifying devices and outriggers and the joint clearance size effect on displacement amplification factor of AVDO were investigated. The amplifying device and the outrigger need to have sufficient stiffness to ensure the amplification effectiveness of AVDO, and it is suggested to reduce the clearance in the pin joint wherever applicable.

Experimental Analysis on Dynamic Response of X‐Section Piled Raft Composite Foundation under Cyclic Axial Load for Ballastless Track in Soft Soil

Large‐scale model tests were established at a scale of 1/5 using a 7 m deep model tank with cross‐sectional dimension of 5 m × 4 m, to study the vibration response characteristics of ballastless track, embankment, and X‐section piled raft foundation under cyclic axial load, including the vibration displacement, velocity, dynamic soil, and pile stress. Cyclic dynamic loading can be achieved by controlling the loading frequency and cycles through the vibration servo control loading system. The test results are presented in the variation of dynamic displacement, velocity, and stress of X‐section piled raft composite foundation. The vibration displacement, velocity, and stress of the track, embankment, and pile foundation follow a pattern of vibration characteristics of loading sine wave. The vibration characteristics of loading waves can be identified easily from the peaks and troughs in the dynamic response of displacement, velocity, and stress at many locations of track slab, embankment, cushion, and underlying soil, at which the vibration response presents almost monotonically increasing tendency with the loading frequencies. With the increase of loading frequency, the vibration responses at the track structure and embankment have higher increasing rates than those at substructure (raft, cushion, and subsoil). The piled raft bears more dynamic load than cushion and subsoils, to ensure long‐term dynamic stability and safety of the foundation soils. The model testing results provide a better understanding of the dynamic response characteristics of ballastless track, embankment, and X‐section piled raft foundation under cyclic axial load in soft soil.

Undrained Responses of Partially Saturated Sand Induced by Biogas under Dynamic Cyclic Loading

Abstract Desaturation denotes a methodology used to mitigate sand liquefaction. Signifying a new form of material, biogas is deemed more feasible for the purpose of desaturation. The present study entailed the adoption of a microbial denitrification process for generating nitrogen gas to induce specimens that are partially saturated. These specimens were utilized for the consolidated undrained triaxial tests performed isotropically. Based on a simplified process concerning the evaluation of liquefaction, the study provided the crucial degree of saturation for determining its minimum degree for averting liquefaction under varying intensities of earthquake. According to test findings, the soils’ liquification resistance grows with an increase in the saturation degree. The number of loading cycles used for initializing liquefaction increases to 34 cycles from 18 cycles under undrained asymmetricity as the extent of saturation reduces to 95.9 % from 100 % when the similarity of stress ratio is observed. Furthermore, the ratio of liquification resistance goes up in a linear pattern initially as the degree of saturation decreases. Meanwhile the ratio declines as the relationship becomes increasingly nonlinear. As a result, there is a gradual reduction in liquefaction resistance as the magnitude of earthquake rises, with a decline in the critical saturation degree. Notably, the extent of this decline is predicated on the relative density.

Influence of Cyclic Impact Loading and Axial Stress on Dynamic Mechanical Properties of Burst‐Prone Coal

High in‐situ stress and frequent dynamic disturbances caused by the mining process in deep coal mines can easily induce dynamic disasters such as coal burst. We conducted laboratory experiments to assess the effects of the axial stress loading and dynamic cyclic impact loading on the dynamic mechanical properties of burst‐prone coals by using a modified split Hopkinson pressure bar (SHPB). Comparisons were made using two types of burst‐prone and burst‐resistant coal samples. The mineral components, organic macerals, and dynamic mechanical features of both burst‐prone and burst‐resistant coal samples were comparatively analyzed based on the obtained X‐ray diffraction (XRD), optical microscope observations, and dynamic compressive stress‐strain curves, respectively. The results of the microstructure analysis indicated a larger difference between the minimum and maximum reflectances of vitrinite for burst‐prone coal. Compared to the burst‐resistant coal samples, the burst‐prone coals contained less corpocollinite and fusinite. While applying a high axial static load combined with cyclic impact load, the coal samples showed the characteristics of fatigue damage. The results also demonstrated that preaxial stress affected the burst resistance of coal samples. The greater the preaxial stress was, the less the coal samples could withstand the dynamic cyclic impact load. In comparison to the burst‐resistant coal sample, the burst‐prone coal sample showed a larger dynamic compressive strength and a lower deformation. They were also more positively capable of the propagation and activation of the coal burst. We believe that the results of the study are conducive to further understanding of the distribution of microcomponents of burst‐prone coals. The results are also beneficial for realizing the dynamic mechanical characteristics of burst‐prone coals under the impact of cyclic dynamic load.

Large-scale asymmetric pulverisation of fault zone: Insights from rock axial strain in static and dynamic loading conditions

The open question of asymmetric large-scale pulverisation of fault zone was experimentally investigated in this paper. It is found that the transition of rock fracture from local splitting to pervasive pulverisation is controlled by strain both in quasi-static and dynamic conditions. This can explain the asymmetric damage in the fault zone as the strain threshold to pulverisation for stiffer rock is lower. In terms of the cyclic dynamic loadings, four types of fracture patterns (lateral tension, axial split, spatial fragmentation, and pervasive pulverisation) were developed with the increase of strain. Subject to the long-term quasi-static and dynamic load, the cumulative damage to the fault zone broadens the scale of pulverisation. In light of the linear correlation of energy absorption to strain, the damage relationships between strain and loading cycles were established and found to offer a good prediction of experimental data.

A supplemental screw enhances the biomechanical stability in medial open-wedge high tibial osteotomy

BackgroundThe supplemental screw technique was introduced for salvage of lateral hinge fracture in medial open-wedge high tibial osteotomy (owHTO). The efficacy of its use in protection of lateral hinge fracture and corresponding biomechanical behaviors remained unclear. The current study was aimed to clarify if a supplemental screw can provide better protection to lateral hinge in biomechanical perspective.MaterialsAn in vitro biomechanical test was conducted. Tibial sawbones, commercial owHTO plates and a cannulated screw were utilized for preparing the intact, owHTO, and owHTO with cannulated screw insertion specimens. A “staircase” dynamic load protocol was adopted for axial compressive test with increasing load levels to determine structural strength and durability by using a material testing system, while a motion capture system was applied for determining the dynamic changes in varus angle and posterior slope of the tibia plateau with various specimen preparation conditions.ResultsType II lateral hinge fracture were the major failure pattern in all specimens prepared with owHTO. The insertion of a supplemental cannulated screw in medial owHTO specimens reinforced structural stability and durability in dynamic cyclic loading tests: the compressive stiffness increased to 58.9–62.2% of an intact specimen, whereas the owHTO specimens provided only 23.7–29.2% of stiffness of an intact specimen. In view of tibial plateau alignment, the insertion of a supplemental screw improved the structural deficiency caused by owHTO, and reduced the posterior slope increase and excessive varus deformity by 81.8% and 83.2%, respectively.ConclusionThe current study revealed that supplemental screw insertion is a simple and effective technique to improve the structural stability and durability in medial owHTO.