Progressive Loading Research Articles

Characteristics of Pressure Stimulated Current and Damage Evolution of Granite under Progressive Uniaxial Loading

The application of load on rock materials stimulates a weak current known as Pressure Stimulated Current (PSC). This study focuses on investigating the damage evolution of granite rocks through the analysis of PSC responses. Uniaxial loading experiments were conducted on granite samples, and the accompanying PSC was measured in real-time. The relationship between PSC characteristics and mechanical behaviors of granite was examined to explore precursory information related to granite failure. The damage evolution of granite was assessed using a damage variable defined as the cumulative charge (time integral of PSC). The results clearly demonstrate a close correlation between the variation of PSC and the mechanical behaviors of rock. Specifically, during the compaction and elastic deformation stages, PSC exhibits a slow and linear increase. However, once deformation enters the plastic stage, PSC demonstrates an accelerated upward trend. Additionally, it was observed that a stress drop coincides with an abnormal increase in PSC, which is followed by a rapid decay. The fluctuation observed after the abnormal increase in PSC during the accelerated growth phase can serve as a precursor of rock failure. Furthermore, the cumulative charge quantity effectively correlates with the damage process of granite samples. The stress–strain curve obtained from a theoretical constitutive model, established based on the damage variable represented by normalized cumulative charge, aligns reasonably well with the experimental results, affirming that the defined damage variable accurately reflects the damage evolution process of rocks. It is hypothesized that PSCs are carried by electrons within the rocks, which are stimulated by electron diffusion during deformation and experience a sharp increase upon rock fracturing. The research findings hold theoretical significance for predicting rockburst incidents using the PSC method.

Rehabilitation of Annular Pulley Injuries of the Fingers in Climbers: A Clinical Commentary.

The annular pulley ligaments of the fingers are one of the most injured anatomical structures in those who participate in climbing. Despite this, there is a paucity of guidance clearly describing the rehabilitation and physical preparation parameters to return to sport following such injuries. The foundation of effective rehabilitation is the judicious application of progressive loading to increase the morphological and material properties of the damaged tissues. We maintain the optimal management of the climbing athlete after a traumatic annular flexor pulley system rupture should be grounded in the principles of strength and conditioning.

Progressive Loading Test for Posterior Ankle Conditions: a novel clinical protocol

Progressive Loading Test for Posterior Ankle Conditions: a novel clinical protocol

Six months of resistance training improves heart rate variability in the elderly.

Heart rate variability is a non-invasive method of assessing global health through the analysis of the autonomous centralnervous system, including both the sympathetic and parasympathetic systems. The aim of this study was to evaluate the effect of resistance training on heart rate variability at rest in elderly individuals undergoing six months of resistance training with progressive loads. Training reduced the body fat percentage of the volunteers (pre: 39.39 ± 7.21 vs post: 34.97 ± 6.40%; p = 0.0069). There was also a significant reduction in the low-frequency index (pre: 69621.50 ± 9817.28 vs post: 54210.50 ± 14903.94; p = 0.0322) and a significant increase in the high-frequency index (pre: 30308.00 ± 9857.86 vs post: 45627.10 ± 14838.80; p = 0.0326). We concluded that sixmonths of resistance training with progressive loads were beneficial for heart rate variability and reduced the body fat percentage in the elderly.

Comparative assessment of a multitudinal piezo arrangement for non-destructive evaluation of construction steel: An experimental study

Recently, sensor-based health diagnostic methods have attracted remarkable attention and can be replaced with conventional nondestructive techniques due to their robustness, reliability, and ease of implementation. Multisensing, reusable, and non-bonded configurations of PZT patches for impedance-based health monitoring are gaining popularity because of their simplicity and robustness. However, the steel bar's complex or uneven surface restricts the PZT patch's direct bonding to the host structure. This article evaluates the effectiveness of different multisensing configuration of PZT patch to monitor the loading effect and structural damage in constructional steel rebar, i.e., surface bonded, clamped and metal wire (MW) attached. Statistical and piezo frequency-based damage indices were used to assess the PZT's effective configuration. The experimental findings of this study have shown the efficacy of multi modal piezo configuration for monitoring damage and loading effects, particularly. Furthermore, the study has expanded to find piezo-equivalent structural parameters for multitudinal piezo position to identify its suitability and effectiveness for better structural health assessment and monitoring. The comparison of indices was highlighted to find a more productive PZT configuration for sensing structural change and damage highlighting the effectiveness of the non-bonded PZT patch configuration. The overall results demonstrate good agreement of employing multisensing array for monitoring damage and progressive loading, specifically the non-bonded configuration of the PZT patch.

Behavior of hybrid FRP-concrete-steel double-skin tubular beams with ultra-high strength concrete and PBL shear connectors under bending

Hybrid double-skin tubular beams (DSTBs) with the external fiber-reinforced polymer (FRP) tube-annular concrete-inner steel tube configuration have excellent mechanical performance and corrosion resistance, but are prone to slip problems. In this study, perfobond shear connectors (PBLs) are proposed to reduce the slip between infilled concrete and inner steel tube. Moreover, using ultra-high strength concrete (UHSC) as the annular material could further improve the structural performance and magnify the lightweight merit of hybrid DSTBs, while hybrid DSTBs with PBLs and UHSC have not been investigated yet. To this end, three-point bending experiments were conducted to hybrid DSTBs with PBLs and UHSC to study the flexural behavior. The mid-span load–deflection curves revealed a three-branched behavior: (i) a first linear ascending branch up to the first yielding at the extreme tension fiber of inner steel tube; (ii) a transition branch to the peak load with a significant slope deterioration when infilled concrete in the compression side reached the unconfined failure strain; (iii) a post-peak residual branch characterized by progressive load reductions over a number of load plateaus. The adoption of UHSC could significantly delay the plastic hinge formation in inner steel tube, and meanwhile improve the bond with PBLs. Thus, the slips between infilled concrete and inner steel tube were minimal (less than 0.2 mm) for most of the specimens, except for those with foamy sheet insertions between PBLs (at around 1 mm). In the end, the design loads of the hybrid DSTBs were predicted by a sectional analysis with high level of accuracy (average error at 6%).

Tribological and mechanical properties of ZrxNy films obtained by HiPIMS in DOMS mode

Maritime transportation represents one of the biggest industries worldwide. The functionality improvement of critical ship parts such as sea chest gratings could mean substantial impacts in fuel consumption reduction, larger lifetime span or reduction of non-indigenous sea species transportation. Since 2008, the ban imposed by the international maritime organization over polluting products, especially tributyltin, created the need to explore new sustainable and environmentally friendly alternatives. Multifunctional coatings have the potential to overcome this situation, creating highly tuneable materials able to combine properties according to the naval industry's needs. Zirconium nitride is known for its reliable mechanical and anti-corrosion properties, critical in a multifunctional coating used in the sea. In the present study, this material was obtained through high-power impulse magnetron sputtering technology in a reactive atmosphere (R-HiPIMS). SEM, EDS, AFM and XRD were used to assess the coatings. Also, the films’ mechanical properties and adhesion were assessed via nanoindentation and progressive load scratch tests, respectively. The pin-on-disk test was used to assess the coatings' tribological properties under dry and wet (3.5% wt. NaCl solution) conditions. The results demonstrate that the increase in hardness was directly influenced by the changes in the structure promoted by the nitrogen rise, from 16 GPa to 25 GPa, with a nitrogen increase in film composition from 47% to 54%. Besides, the tribological tests revealed the key role of an oxygen-rich tribolayer and surface roughness features (skewness and kurtosis) in keeping the film’s integrity. The ZrxNy films obtained by HiPIMS improved the mechanical and tribological properties compared to ZrN obtained by DCMS, opening new possibilities to be explored as a solution inside a multifunctional coating system.

A honeycomb panel-based protective device for steel parking structure against transverse impact

With escalating demand for urban parking structures, the columns within these structures are more susceptible to hazards resulting from vehicle collisions compared to other public buildings. Moreover, it is crucial to emphasize the significant increase in the risk of collapse in parking structures subjected to vehicle collisions, primarily owing to their heightened dynamic response and low required bearing capacity. Consequently, to prevent vehicles from directly crashing on the columns, besides providing an alternate load path, urgent implementation of protective measures utilizing energy-absorbing materials is necessary for parking structures. This study proposes a honeycomb panel-based (HP) protective device for steel parking structures aimed at absorbing energy and mitigating damage resulting from vehicle collisions. A simplified multi-scale simulation, considering reasonable material models and boundary conditions, is employed to study the performance of parking structures under transverse impact. The deformation patterns, impact loads, transverse deflections, internal energies, and horizontal reactions are compared for the parking structures with and without the HP protective devices. Innovatively, a classical progressive collapse loading scheme is employed to simulate the vertical residual resistance of the beam-column substructure after the transverse impact. Finally, a comprehensive investigation is conducted on the effects of critical parameters of HP protective device. The results demonstrate that a properly designed HP protective device can significantly enhance the resistance of parking structures to transverse impact, thereby effectively mitigating the risk of progressive collapse in such structures after impact.

Mechanical evaluation of different sagittal osteotomy fixation techniques used in minimally invasive surgery

Minimally invasive orthognathic surgery has advantages such as faster recovery, less paresthesia, and lower morbidity in the immediate postoperative period. However, there is no consensus regarding which fixation method is safer. The aim of the present study is to compare different methods of fixation of the short sagittal osteotomy like the Cordier G modification performed in minimally invasive surgery. An in vitro study was performed, consisting of 54 standardized polyurethane synthetic hemimandibles with Short sagittal osteotomy divided into 6 groups comprising 09 hemimandibles each. The groups consisted of bicortical screws, 4-hole straight plates, 0.8 mm and 1.0 mm thick curved plates, and 0.8 mm thick double Y and 1.0 mm thick double Y plates. All groups are System 2.0 and trademark Artfix®. The loading test was carried out, at a speed of 1mm/min, with a 50 Kgf load note for progressive load application on the system. Peak load (Kgf) and peak displacement (mm) were evaluated. Greater load resistance was found in the groups that received bicortical screws and 0.8mm and 1.0mm thick double Y plates.

Comparability of the Effectiveness of Different Types of Exercise in the Treatment of Achilles Tendinopathy: A Systematic Review.

Achilles tendinopathy (AT) is a common condition both in athletes and the general population. The purpose of this study is to highlight the most effective form of exercise in managing pain-related symptoms and functional capacity as well as in a return to life activities, ensuring the quality of life of patients with AT, and creating a protocol to be used in rehabilitation. We conducted a systematic review of the published literature in Pubmed, Scopus, Science Direct, and PEDro for Randomised Controlled Trials concerning interventions that were based exclusively on exercise and delivered in patients 18-65 years old, athletes and non-athletes. An amount of 5235 research articles generated from our search. Five met our inclusion criteria and were included in the review. Research evidence supports the effectiveness of a progressive loading eccentric exercise program based on Alfredson's protocol, which could be modified in intensity and pace to fit the needs of each patient with AT. Future research may focus on the optimal dosage and load of exercise in eccentric training and confirm the effectiveness of other type of exercise, such as a combination of eccentric-concentric training or heavy slow resistance exercise. Pilates could be applied as an alternative, useful, and friendly tool in the rehabilitation of AT.

Aerobic power across positions - an investigation into women's soccer performance.

The aim of the study was to discern the disparities in the aerobic capacity of female athletes occupying various positions within a soccer team, and to understand the physical characteristics of the athletes in different positions. It is critical to understand that the physical demands for players vary depending on their positions on the field, a factor that greatly influences their training and gameplay. The study engaged a sample of 25 female soccer players, average age of 22.72 (±2.69 SD), all of whom were active participants in the Chinese Women's Super League. The sample was distributed across several playing positions, including forwards, midfielders, and defenders. To gather pertinent data on oxygen uptake, a progressive load test was administered on a treadmill, coupled with a gas analyzer to amass respiratory indices (JAEGER, Germany). The study revealed that there was a notable variance in the maximum oxygen uptake among players in different positions. The midfielders exhibited the highest VO2 max at 63.24±7.04 ml/kg/min, followed by the forwards who averaged at 58.92±7.70 ml/kg/min, and finally the defenders who recorded the smallest average at 55.73±4.40 ml/kg/min. The outcomes of this study indicate that the positional role of a player in a team correlates with their aerobic capacity. Therefore, the positional demands significantly shape the player's physical characteristics, influencing their training and gameplay. This understanding is vital for the optimal conditioning of athletes in different positions in the sport of soccer.

Anatomic and Biomechanical Study of the Forearm Interosseous Membrane, Distal Oblique Bundle, and Triangular Fibrocartilage Complex: Role in Galeazzi Fracture Dislocation

The purpose of this study was to measure distal radioulnar joint (DRUJ) dislocation and radioulnar displacement associated with sequential sectioning of the different bands of the interosseous membrane and triangular fibrocartilage complex in the simulation of a Galeazzi fracture dislocation. Twelve fresh-frozen cadaver forearms were dissected. We examined the anatomy and function of the forearm interosseous membrane. Each forearm was then mounted onto a biomechanical wrist and forearm device. In the control group, radial osteotomy was performed and the degree of DRUJ displacement with progressive loads was measured. In addition to radial osteotomy, in group 1, the central band (CB) was sectioned; in group 2, the CB, distal membranous portion of the interosseous membrane, and distal oblique bundle were sectioned; and in group 3, the CB, distal membranous portion of the interosseous membrane, distal oblique bundle, and triangular fibrocartilage complex were sectioned. The radioulnar displacement (mm) at 25 N, 50 N, and 75 N was recorded. In group 1, applying progressive loads resulted in an average DRUJ displacement of 4.3, 5.9, and 7.9 mm, respectively. In group 2, the displacement was 5.2, 5.7, and 6.9 mm, respectively. In group 3, the displacement was 6.2, 8.1, and 9.9 mm, respectively. Our study showed a correlation between increase in the load applied to the same injury and the degree of displacement (P= .001). In group 3, the degree of DRUJ displacement was statistically increased compared to the other groups (P= .04). Migration of the radius under loads implies disruption of both the CB and triangular fibrocartilage complex. The distal oblique bundle by itself does not seem to have a relevant role in radioulnar displacement at the DRUJ. This study provides insights into the interosseous membrane and stability of the DRUJ, which can contribute to a better understanding of Galeazzi fracture-dislocations.

High-Intensity Functional Training Induces Superior Training Adaptations Compared With Traditional Military Physical Training.

Helén, J, Kyröläinen, H, Ojanen, T, Pihlainen, K, Santtila, M, Heikkinen, R, and Vaara, JP. High-intensity functional training induces superior training adaptations compared with traditional military physical training. J Strength Cond Res 37(12): 2477-2483, 2023-This study examined the effectiveness of concurrent strength and endurance training with an emphasis on high-intensity functional training (HIFT) during military service. Voluntary male conscripts (aged 18-28 years) were placed in either an experimental (EXP: n = 50-66) or a control (CON: n = 50-67) group. The training for the EXP group included HIFT using body mass, sandbags, and kettlebells. The CON group trained according to the current practice. Physical performance and body composition were assessed at baseline (PRE), at week 10 (MID), and after (POST) the 19-week training period. Significance was set at p < 0.05. The total distance covered in a 12-minute running test increased in both groups, but the change in EXP was superior to the change in CON (11.6%, ES: 0.79 vs. 5.7%, ES: 0.33; p = 0.027). Maximal strength and power characteristics increased in EXP (3.1-5.0%), whereas no improvements were observed in CON. Conscripts with the highest initial fitness showed no improvements in physical performance in either group. Body mass and waist circumference decreased in EXP, whereas CON showed an increase in muscle mass. These findings suggest that HIFT is an effective and time-efficient approach to improve soldiers' aerobic fitness during military service. For the optimal development of strength, the training equipment used may not have provided sufficient and progressive loading to yield considerable strength adaptations. More focus should be placed on sufficient intensity and volume in both strength and endurance training, especially for the most fit soldiers.

Laboratory experiments on rock salt and phenomenological observations

We conducted an experimental campaign on salt samples from three different geographic origins. Short-term strain-controlled tests and constant mean stress tests, as well as long creep tests were performed. For reliable rock characterization and constitutive modeling, the experimental results should be analyzed considering heterogeneity. This is particularly important for the volumetric strains and the dilatancy onset (an important design criterion of underground facilities in salt formations). Heterogeneity can be quantified by the use of different measurement techniques, capturing the sample response at different scales. Material heterogeneity, due to the presence of impurities, can explain the differences observed between local and global measurements that cannot be justified by the heterogeneity induced by sample-piston friction. The volumetric strains measured during the isotropic phase are not negligible compared to those of the deviatoric phase, and the analysis of the isotropic phase can explain some of the differences observed among tests performed under equivalent conditions. To reduce bias, all samples should undergo the same preconditioning process. Long creep tests performed at constant stress deviator and short-term tests show that the mean pressure effect on the deviatoric response is of the same order of magnitude than natural variability. Reverse creep, a transient phenomenon that could be active when the stress deviator decreases, has a smaller amplitude than the associated elastic drop, and can be analyzed not only during creep tests, but also during unloading–reloading cycles, which are characterized by a progressive load drop, more representative of in situ conditions.

Mechanical effect of abrasives on silicon surface in chemo-mechanical grinding

To obtain high-quality surfaces and subsurfaces of ground silicon wafers, chemo-mechanical grinding (CMG) for silicon has been developed by inducing chemical reactions into grinding. Chemical reactions between abrasives and silicon during CMG process have been proved in previous studies. The mechanical effect of abrasives in CMG process is not fully understood. To investigate abrasives’ mechanical effect on material removal and subsurface damage of silicon in CMG process, silicon nanoscratching experiments with CeO2 indenter under a progressive normal load were conducted, and microtopographies of scratch surface and subsurface were observed. For comparison, silicon nanoscratching experiments with diamond indenter were also conducted. Finite element models of silicon nanoscratching with CeO2 and diamond indenters were built to investigate the relationship between stress distribution and damage evolution of silicon. Experimental investigations and simulation results indicate that no obvious material removal of silicon or serious subsurface damage is generated by CeO2 indenter's mechanical action because the wear of CeO2 indenter leads to the release of the stress on silicon. Material removal of silicon during CMG process relies on chemical reactions between soft abrasives and silicon other than stress on silicon generated by soft abrasives.

Comparative Study of Mechanical Performance of AlCrSiN Coating Deposited on WC-Co and cBN Hard Substrates

The objective of this study is to explore and compare the mechanical response of AlCrSiN coatings deposited on two different substrates, namely, WC-Co and cBN. Nano-indentation was used to measure the hardness and elastic modulus of the coatings, and micro-indentation was used for observing the contact damage under Hertzian contact with monotonic and cyclic (fatigue) loads. Microscratch and contact damage tests were also used to evaluate the strength of adhesion between the AlCrSiN coatings and the two substrates under progressive and constant loads, respectively. The surface damages induced via different mechanical tests were observed using scanning electron microscopy (SEM). A focused ion beam (FIB) was used to produce a cross-section of the coating–substrate system in order to further detect the mode and extent of failure that was induced. The results show that the AlCrSiN coating deposited on the WC-Co substrate performed better in regard to adhesion strength and contact damage response than the same coating deposited on the cBN substrate; this is attributed to the lower plasticity of the cBN substrate as well as its less powerful adhesion to the coating.

Failure analysis and structural reliability of unreinforced masonry veneer walls: Influence of wall tie corrosion

Corrosion appears to be a very common problem in historical and aged structures with steel ties and anchorages. A potential rapid deterioration of the wall tie due to the corrosion leading to a premature structural failure poses a serious threat to the built heritage infrastructures’ safety. This paper describes an overview of the probabilistic failure analysis of the unreinforced masonry (URM) veneer wall system with flexible backup under uniformly distributed out-of-plane loadings. Moreover, a framework is proposed to consider the wall tie corrosion in the stochastic finite element analysis (FEA) while estimating the structural reliability. A probabilistic experimental study where 18 full-scale URM veneer wall systems with theoretically identical geometries and properties were tested under inward and outward lateral loading. Wall failure statistics along with the probabilistic characterisation of veneer wall constituent materials including mortar, wall tie and timber were accomplished. A stochastic computational model was then developed which combines the FEA and Monte Carlo simulation to evaluate the failure progression and system peak load (veneer capacity) while considering the spatial variability of veneer wall material properties. Two scenarios, with and without wall tie corrosion, are considered, and the probabilistic characterisation of the veneer capacities for these scenarios under inward and outward out-of-plane loading is also reported. The model error statistics were combined with the probabilistic load models to determine the reliability index corresponding to the Australian Standard for Masonry Structures AS 3700. Annual reliabilities are compared to target reliabilities recommended by ISO 2394. Capacity reduction factor and design minimum tie strength consideration for corroded wall tie is also discussed.

Patellofemoral Joint Loading Progression Across 35 Weightbearing Rehabilitation Exercises and Activities of Daily Living

Background: Exercises that provide progressive therapeutic loading are a central component of patellofemoral pain rehabilitation, but quantitative evidence on patellofemoral joint loading is scarce for a majority of common weightbearing rehabilitation exercises. Purpose: To define a loading index to quantify, compare, rank, and categorize overall loading levels in the patellofemoral joint across 35 types of weightbearing rehabilitation exercises and activities of daily living. Study Design: Descriptive laboratory study. Methods: Model-estimated knee flexion angles and extension moments based on motion capture and ground-reaction force data were used to quantify patellofemoral joint loading in 20 healthy participants who performed each exercise. A loading index was computed via a weighted sum of loading peak and cumulative loading impulse for each exercise. The 35 rehabilitation exercises and daily living activities were then ranked and categorized into low, moderate, and high “loading tiers” according to the loading index. Results: Overall patellofemoral loading levels varied substantially across the exercises and activities, with loading peak ranging from 0.6 times body weight during walking to 8.2 times body weight during single-leg decline squat. Most rehabilitation exercises generated a moderate level of patellofemoral joint loading. Few weightbearing exercises provided low-level loading that resembled walking or high-level loading with both high magnitude and duration. Exercises with high knee flexion tended to generate higher patellofemoral joint loading compared with high-intensity exercises. Conclusion: This study quantified patellofemoral joint loading across a large collection of weightbearing exercises in the same cohort. Clinical Relevance: The visualized loading index ranks and modifiable worksheet may assist clinicians in planning patient-specific exercise programs for patellofemoral pain rehabilitation.

Thermal evolutions of residual stress and strain hardening of GH4169 Ni-based superalloy treated by laser shock peening

Residual stresses and strain hardening in GH4169 Ni-based superalloy treated by four different laser shock peening (LSP) configurations and their thermal evolution behaviors under two vacuum annealing conditions were investigated with X-ray diffraction (XRD) and two uniaxial progressive loading tests with two loading rates. Results showed that the thermal relaxations of residual stress under the two vacuum annealing conditions are quite limited, which can be attributed to the fairly low strain hardening levels (<3 %) produced by the current LSP configurations. Besides, an abnormal elevation of strain hardening under vacuum annealing condition VA2 (650 °C, 12 h) was observed, which is caused by the precipitation and growth of plate-like δ-phase particles at the grain boundaries (GBs) and the twin boundaries (TBs). Last but not least, the characteristic relationship between strain hardening and XRD peak width calibrated in this study can also be used to quantitatively study strain hardening of GH4169 Ni-based superalloy in the same heat treatment state treated by other cold working processes below 650 °C.

Scratch behaviors of polyacrylate-based hard coatings on alternating multi-layered PMMA+PC substrates

In our previous work [1], the scratch behaviors of alternating multi-layered polymethyl methacrylate (PMMA)/polycarbonate (PC) laminates were studied. Generally, a hard coating layer must be introduced to the surface of PMMA + PC laminate to further enhance its hardness and scratch resistance. In this work, the same laminates used in our previous work were coated by a UV-cured polyacrylate hard layer, and the scratch behaviors and relating mechanisms of hard coating (HC) systems were investigated via both progressive normal load scratch test and pencil hardness test. Sliding counterfaces of two tests were stainless steel ball with a diameter of 1 mm and cylinder made of pencil core with a diameter of 2 mm, respectively. Length, width and thickness of test specimen were 150 mm, 33 mm and 1.6 mm, respectively. The effects of HC's thickness and substrate's hardness on scratch behaviors of HC systems were also included. In both scratch tests, experimental results demonstrated that scratch damages of HC systems were featured with dense periodic cracks. Finite element modeling (FEM) revealed that the formation of such crack types was attributed to the maximum principal stress perpendicular to crack propagation direction. Furthermore, it was found that the scratch resistances of HC systems were enhanced as thickness of HC or hardness of substrate increased, the mechanism behind which were found to be decreasing of the maximum principal stress and consequent delaying of crack formation as revealed through FEM.