Uniaxial Force Research Articles

Comparison of Vertical Jump Force–Time Metrics Between ACL-Injured and Healthy Semi-Professional Male and Female Soccer Players

Given the increasing use of innovative force plate systems in applied sports settings and the impact that anterior cruciate ligament (ACL) injuries have on team success, the purpose of the present study was to compare the lower-body neuromuscular performance characteristics of athletes who underwent ACL reconstruction (ACLR) and their non-injured counterparts (i.e., healthy controls). Forty-five male (thirteen injured) and twenty-six female (ten injured) semi-professional soccer players volunteered to participate in the present study. Each athlete performed three countermovement vertical jumps (CMJs) while standing on a uniaxial force plate system sampling at 1000 Hz. The injured athletes completed a nine-month recovery protocol and were screened 11–13 months post-ACLR. The dependent variables included the force–time metrics within both the eccentric and concentric phases of the CMJ. Independent t-tests or Mann–Whitney U-test were used to examine statistically significant (p < 0.05) differences in each variable (i.e., ACL-injured vs. healthy controls). The results revealed no significant between-group differences in any CMJ force–time metrics of interest (e.g., concentric peak force, eccentric mean power, countermovement depth) between ACL-injured and non-injured athletes, including inter-limb asymmetry measures (i.e., peak takeoff and landing force). Besides implying the effectiveness of the implemented rehabilitation protocol, these findings suggest that the CMJ may not present a sufficient neuromuscular performance stimulus needed to expose lower-limb asymmetries and strength and power deficiencies 11–13 months post-ACLR.

Dynamic mesophase transition induces anomalous suppressed and anisotropic phonon thermal transport

The physical/chemical properties undergo significant transformations in the different states arising from phase transition. However, due to the lack of a dynamic perspective, transitional mesophases are largely underexamined, constrained by the high resource burden of first principles. Here, using molecular dynamics (MD) simulations empowered by the machine-learning potential, we proffer an innovative paradigm for phase transition: regulating the thermal transport properties via the transitional mesophase triggered by a uniaxial force field. We investigate the mechanical, electrical, and thermal transport properties of the two-dimensional carbon allotrope of Janus-graphene with strain-engineered phase transition. Notably, we found that the transitional mesophase significantly suppresses the thermal conductivity and induces strong anisotropy near the phase transition point. Through machine-learning-driven MD simulations, we achieved high-precision atomic-level simulations of Janus-graphene. The results show that thermal vibration-induced intermediate amorphous or interfacial phases induce strong and anisotropic interfacial thermal resistance. The investigation not only endows us with a novel perspective on mesophases during phase transitions but also enhances our holistic comprehension of the evolution of material properties.

Numerical Approach to Determine the Resistance of Threaded Anchors in Ultra-High-Performance Fiber-Reinforced Cementitious Composite

Due to their relatively high tensile strength and dense matrix, UHPFRCs have proven to be a highly effective building material for both strengthening existing reinforced concrete structures and constructing new ones. In both cases, the use of fasteners is prevailing, with threaded anchors being frequently employed. The thicknesses of structural components made of UHPFRCs are relatively thin, i.e., at least 30 mm, typically 50 to 100 mm, and exceptionally 100 to 200 mm. Therefore, the aim is to use fasteners with short anchorage lengths. In this study, the structural behavior of a short threaded anchor with a 20 mm diameter and an embedment length of 50 mm (2.5 Ø) in a UHPFRC is investigated using non-linear finite element models. The UHPFRC is assumed to exhibit tensile strain-hardening behavior, with tensile strengths of 7 MPa and 11 MPa, respectively. The modeled anchor was subjected to a continuously increasing uniaxial pull-out force. The results indicate that the fracture mechanism of threaded anchors in UHPFRCs is primarily characterized by the formation of a tensile membrane within the UHPFRC, which acts as the main resisting element against the pull-out force. Additionally, the influence of the UHPFRC’s tensile properties on the pull-out behavior and ultimate resistance of the threaded anchors was determined.

Is Countermovement Jump an Indirect Marker of Neuromuscular Mechanism? Relationship with Isometric Knee Extension Test.

Several studies have shown that force application is influenced by different neuromuscular mechanisms depending on the time of force application analysis in isometric knee extension test (IKE), and a countermovement jump (CMJ) has contributions from knee extension, so some CMJ variables could be indicators of such mechanisms. Purpose: The aim of this study was to determine the level of relationship of variables of IKE and bilateral CMJ tests. Methods: Male college soccer players (n = 25; corporal mass = 72 ± 8 kg; height = 171 ± 5 cm; age = 22 ± 2 years) performed the IKE at two angles (60° and 75°) on an isokinetic machine and the CMJ on two uniaxial force platforms. To determine the level of relationship, Pearson's correlation coefficient was analyzed between the test variables. Results: Trivial to moderate correlations (r = -0.45 to 0.62; p < 0.05) were found between CMJ variables and IKE in both knee angles (60° and 75°); Conclusions: The variables of IKE have a trivial to moderate correlation with the variables of CMJ, so the variables of CMJ could not be considered interchangeably with those of IKE and therefore considered indicators of neuromuscular mechanisms isolated from the knee extensor function. Longitudinal design (fatigue or training protocols) should be realized to corroborate these results.

Morphological and Performance Biomechanics Profiles of Draft Preparation American-Style Football Players

Background/Objectives: Using advanced methodologies may enhance athlete profiling. This study profiled morphological and laboratory-derived performance biomechanics by position of American-style football players training for the draft. Methods: Fifty-five players were categorized into three groups: Big (e.g., lineman; n = 17), Big–skill (e.g., tight end; n = 11), and Skill (e.g., receiver; n = 27). Body fat (BF%), lean body mass (LBM), and total body mass were measured using a bioelectrical impedance device. Running ground reaction force (GRF) and ground contact time (GCT) were obtained using an instrumented treadmill synchronized with a motion capture system. Dual uniaxial force plates captured countermovement jump height (CMJ-JH), normalized peak power (CMJ-NPP), and reactive strength. Asymmetry was calculated for running force, GCT, and CMJ eccentric and concentric impulse (IMP). MANOVA determined between-group differences, and radar plots for morphological and performance characteristics were created using Z-scores. Results: There was a between-group difference (F(26,80) = 5.70, p &lt; 0.001; Wilk’s Λ = 0.123, partial η2 = 0.649). Fisher’s least squares difference post hoc analyses showed that participants in the Skill group had greater JH, CMJ-NPP, reactive strength, and running GRF values versus Big players but not Big–skill players (p &lt; 0.05). Big athletes had greater BF%, LBM, total body mass, and GCT values than Skill and Big–skill athletes (p &lt; 0.05). Big–skill players had greater GCT asymmetry than Skill and Big players (p &lt; 0.05). Asymmetries in running forces, CMJ eccentric, and concentric IMP were not different (p &gt; 0.05). Morphological and performance biomechanics differences are pronounced between Skill and Big players. Big–skill players possess characteristics from both groups. Laboratory-derived metrics offer precise values of running and jumping force strategies and body composition that can aid sports science researchers and practitioners in refining draft trainee profiles.

Design and Analysis of a 3D Frictional Mechanical Metamaterial for Efficient Energy Dissipation

AbstractThis study introduces a novel frictional mechanical metamaterial composed of a central hexagon or re‐entrant honeycomb frame, a lower section with four tapered columns, and an upper portion with a blade shape. When subjected to an external uniaxial force, the 3D structure of the metamaterial utilizes sliding interactions to dissipate frictional energy. The mechanical properties of the proposed metamaterial, such as load‐displacement relationships, hysteresis area, and peak force, can be fine‐tuned by adjusting geometric parameters and constituent materials. Extensive analysis is conducted through experimental compression tests, finite element (FE) simulations, and theoretical modeling. Comparative assessments of the metamaterial's energy dissipation performance demonstrated a good agreement between experimental and simulation results, with minor variations observed for deeper compression cycles. The proposed metamaterial offers the potential for superior elastic energy absorption and dissipation, making it a promising solution for applications requiring repeated energy dissipation or damping under cyclical loads while maintaining a lightweight profile.

Comparative analysis of mechanical and drilling properties: Human skull vs. 3D-printed replicas for neurosurgical training

Neurosurgery is one of the most difficult surgical disciplines, making neurosurgical simulation crucial for learners. 3D printing is increasingly used for this simulation due to its accessibility and cost-effectiveness compared to conventional methods. Previous studies have qualitatively evaluated the efficacy of 3D printing models for burr hole and craniotomy simulation using surgeon feedback. This study quantitatively evaluates the mechanical properties of human skulls and compares them with 3D-printed skulls to identify the necessary materials and technologies for accurate replication in neurosurgical training. Vickers hardness, compression, and drilling simulation tests were conducted on human cadaveric skulls and 3D-printed models manufactured using Fused Filament Fabrication (FFF), Stereolithography (SLA), and Material Jetting (MJ) technologies. Uniaxial force during a simulated burr hole procedure was measured as drilling progressed through the outer table (OT), diploë and inner table (IT) of the skull. The results showed that different 3D printing technologies and materials have qualities corresponding to each of the three layers of the human skull. For instance, the White Resin 40 model was the closest match to the OT of human skull, exhibiting the lowest mean difference of drilling modulus of 1.98. The OT of the human skull had a Vickers hardness of 38.6 ± 5 HV0.05. The closest 3D-printed models were SLA White at 16.6 ± 0.3 HV0.05 and Rigid 10K at 65.7 ± 3 HV0.05. In terms of mechanical properties, the human skull demonstrated a compression modulus that closely matched the SkullSTN 2, PC 60, PEEK 40, and PEEK 60, with differences of less than 0.1 GPa. These findings demonstrate the effectiveness of drilling simulation tests in evaluating various materials and infills to refine models before neurosurgeon evaluation, enabling the identification of an optimal 3D-printed training model for simulating burr hole procedures.

Hydrogel Films with Impact Resistance by Sacrificial Micelle-Assisted-Alignment.

Various strategies are developed to engineer aligned hierarchical architectures in polymer hydrogels for enhanced mechanical performance. However, chain alignment remains impeded by the presence of hydrogen bonds between adjacent chains. Herein, a facile sacrificial micelle-assisted-alignment strategy is proposed, leading to well-aligned, strong and tough pure chitosan hydrogels. The sacrificial sodium dodecyl sulfate micelles electrostatically interact with the protonated chitosan chains, enabling chain sliding and alignment under uniaxial forces. Subsequently, sacrificial micelles can be easily removed via NaOH treatment, causing the reforming of H-bond in the chain networks. The strength of the pure chitosan hydrogels increases 140-fold, reaching 58.9±3.4MPa; the modulus increases 595-fold, reaching 226.4±42.8MPa. After drying-rehydration, the strength and modulus further rise to 70.3±2.4 and 403.5±76.3MPa, marking a significant advancement in high-strength pure chitosan hydrogel films. Furthermore, the designed multiscale architectures involving enhanced crystallinity, well-aligned fibers, strong interfaces, robust multilayer Bouligand assembly contribute to the exact replica of lobster underbelly with impact resistance up to 6.8±1.0kJ m-1. This work presents a promising strategy for strong, tough, stiff and impact-resistant polymer hydrogels via well-aligned hierarchical design.

SolidWorks Simulation Approach for Concrete Pillars Consolidation with CFRP Wraps

This paper presents the results of the Finite Element Analysis using SolidWorks simulation of the strengthening effect of the CFRP wraps applied to the bottom of concrete pillars bearing uniaxial compression forces. The benefits of using CFRP wrap have been emphasized by analyzing the resulting values of Displacement, Strain, and Factor of Safety.

Comparisons of ground reaction force between successful and unsuccessful lifts in snatch and clean-and-jerk in weightlifting

&lt;p&gt;目的：利用符合舉重運動特性的單軸測力平台，探討菁英選手在抓舉與挺舉時，成功與失敗地面反作用力參數之差異。方法：11名大專舉重選手為本研究參與者。參與者進行符合正式比賽規定的抓舉與挺舉動作時，雙腳需分別站立於長2公尺寬1公尺的舉重專用測力平台。每位參與者先完成抓舉再進行挺舉，每次試舉過程利用測力平台收集地面反作用力，並計算各階段力量峰值、發力率、壓力中心前後位移、雙腳寬度距離、右腳力量比例，再進行差異比較。結果：成功抓舉在第一拉期力量峰值、接槓時間顯著大於失敗；高比例的參與者，在接槓期力量峰值亦小於失敗。成功挺舉在上搏接槓期力量峰值顯著小於失敗。結論：失敗最高的階段發生在接槓期。抓舉應提高第一拉期的力量，以爭取更多接槓時間。接槓期應減少負荷力量；在上挺接槓分腿支撐時，可將槓鈴與壓力中心向後移動，並維持壓力中心接近於雙腳跨距中間偏前的位置。舉重專用測力平台能全程給予選手發力方式的回饋，有利於修正技術。&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;&lt;p&gt;Purpose: To explore the differences in ground reaction force parameters between successful and unsuccessful lifts during the snatch and clean-and-jerk using an internally developed uniaxial force platform. Methods: Eleven elite college-level weightlifters were recruited in this study. They were asked to stand on a 2m1m force platform to perform the snatch and clean-and-jerk with self-selected weights by following the official competition rules. The maximal total ground reaction force (vGRF), rate of force development, the center of pressure, feet distance, and force distribution of the right foot were calculated and compared across different phases. Results: In the snatch, the peak vGRF of the first pull and the catching time in successful lifts were significantly higher than in unsuccessful ones. Moreover, the peak vGRF of catching in successful lifts was lower than in unsuccessful lifts. In successful clean-and-jerk, the peak vGRF of catching during clean in successful attempts was lower than in unsuccessful lifts. Conclusion: The phase with the highest failure rate occurred during the catch phase. In the snatch, increasing the force during the first pull may allow for more time in the catching phase. It is also recommended that the loading force should be reduced during the catching phase. In the split jerk, results showed moving the barbell and the center of pressure backward while maintaining the center of pressure slightly forward of the midpoint between the feet can improve stability. It is recommended that during weightlifting training, the internally developed force platform serves as a valuable tool to provide feedback on biomechanical indicators such as force development and help coaches and athletes refine weightlifting techniques in real-time.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Predicting Damage in Notched Functionally Graded Materials Plates through extended Finite Element Method based on computational simulations

Presently, Functionally Graded Materials (FGMs) are extensively utilised in several industrial sectors, and the modelling of their mechanical behaviour is consistently advancing. Most studies investigate the impact of layers on the mechanical characteristics, resulting in a discontinuity in the material. In the present study, the extended Finite Element Method (XFEM) technique is used to analyse the damage in a Metal/Ceramic plate (FGM-Al/SiC) with a circular central notch. The plate is subjected to a uniaxial tensile force. The maximum stress criterion was employed for fracture initiation and the energy criterion for its propagation and evolution. The FGM (Al/SiC) structure is graded based on its thickness using a modified power law. The plastic characteristics of the structure were estimated using the Tamura-Tomota-Ozawa (TTO) model in a user-defined field variables (USDFLD) subroutine. Validation of the numerical model in the form of a stress-strain curve with the findings of the experimental tests was established following a mesh sensitivity investigation and demonstrated good convergence. The influence of the notch dimensions and gradation exponent on the structural response and damage development was also explored. Additionally, force-displacement curves were employed to display the data, highlighting the fracture propagation pattern within the FGM structure.

Changes in Countermovement Vertical Jump Force-Time Metrics During a Game in Professional Male Basketball Players.

Cabarkapa, D, Johnson, QR, Cabarkapa, DV, Philipp, NM, Eserhaut, DA, and Fry, AC. Changes in countermovement vertical jump force-time metrics during a game in professional male basketball players. J Strength Cond Res 38(7): 1326-1329, 2024-As technology within elite basketball advances and is more available to sporting organizations, novel approaches for assessing and addressing athletic performance during practice or competition are being continuously explored. The aim of this investigation was to examine changes in neuromuscular performance during live basketball play. Eight professional male basketball players volunteered to participate in this study. The testing procedures were conducted during a pre-tournament camp over a span of 2 days. During the first day, the athletes were familiarized with the testing procedures, and baseline measurements were obtained. Using a uni-axial force plate system sampling at 1,000 Hz, each athlete performed 3 countermovement vertical jumps (CVJ) without an arm swing before proceeding with their regular training activities. During the second day of the pre-tournament camp, the athletes repeated identical CVJ testing procedures before the start of the first quarter and post-first, second, third, and fourth quarter of a simulated 5-on-5 basketball game. Repeated-measures testing design was used to examine statistically significant differences in various force-time metrics of interest in comparison to the baseline levels (p < 0.05). Besides a trivial decrease in eccentric mean force, the findings of this study revealed no statistically significant changes in any force-time metrics of interest within both eccentric and concentric phases of the CVJ (i.e., mean and peak force and power, jump height, impulse, velocity, and contraction time). Thus, we can conclude that these variables were not sensitive to acute fatigue, suggesting that the neuromuscular performances of professional male basketball players tend to remain unchanged throughout a 5-on-5 simulated game.

Relationship between vertical jump performance and playing time and efficiency in professional male basketball players.

With innovative force plate technology being available to many sports organizations worldwide that allow for time-efficient in-depth neuromuscular performance assessment, the purpose of the present study was to examine the relationship between some of the most commonly analyzed countermovement vertical jump (CVJ) force-time metrics and basketball playing time and efficiency. Twenty-four professional male basketball players volunteered to participate in the present study. The CVJ testing procedures were conducted within the first quarter of the competitive season span. Following a standardized warm-up protocol, each athlete stepped on a dual uni-axial force plate system sampling at 1,000 Hz and performed three maximum-effort CVJs with no arm swing. To minimize the possible influence of fatigue, each jump trial was separated by a 10-15 s rest interval and the average value across three jumps was used for performance analysis purposes. Basketball playing efficiency and average playing time were obtained at the end of the regular season competitive period from the coaching staff records and the official team records. Pearson product-moment correlation coefficients (r) were used to examine the strength of the relationships between force-time metrics and basketball playing time and efficiency, separately for each dependent variable (p < 0.05). A significant positive association was observed between playing efficiency and eccentric mean force and eccentric mean and peak power (r = 0.406-0.552). Similarly, an increase in eccentric mean power was positively correlated with the number of minutes played during the competitive season (r = 0.464). Moreover, the aforementioned relationship remained present even when eccentric mean power was expressed relative to the player's body mass (r = 0.406). Thus, the findings of the present study indicate that, at the professional level of men's basketball competition, CVJ eccentric strength and power have a positive impact on both playing time and efficiency.

Changes in Countermovement Vertical Jump Force-Time Metrics Across Different Competitive Levels in Women’s Volleyball

As one of the most fundamental skills in volleyball, the countermovement vertical jump (CVJ) has been commonly implemented as a non-invasive and time-efficient method for the assessment of lower-body neuromuscular function. The purpose of the present study was to examine differences in CVJ performance between three different competitive levels in female volleyball players (i.e., national team [n=20], professional league [n=16], collegiate [n=16]). While standing on a uni-axial force plate system sampling at 1000 Hz, athletes performed three maximal-effort CVJs with no arm swing (i.e., hands on the hips during the entire movement). Each jump was separated by a 10-15 second rest interval to minimize the possible influence of fatigue. Significantly greater eccentric braking impulse, peak velocity, peak force, mean and peak power, vertical jump height, reactive strength index-modified, countermovement depth, and shorter braking phase, eccentric duration, and contraction times were observed for the national team and professional players when compared to collegiate athletes. Also, national team players demonstrated significantly greater eccentric braking impulse, peak velocity, mean and peak power, reactive strength index-modified, and countermovement depth than professional volleyball players. However, during the concentric phase of the CVJ, the only significant differences observed were between national team players and collegiate athletes, where national team players exhibited significantly greater peak velocity, impulse, and mean and peak power. Thus, it can be concluded that higher-level players may be more capable of effectively utilizing the eccentric phase of the CVJ and executing the stretch-shortening action more rapidly, which contributes to better CVJ height.

Comparison of vertical jump and sprint performances between 3 × 3 and 5 × 5 elite professional male basketball players.

Given its fast-growing popularity and unique on-court competitive demands, 3 × 3 basketball has captured a considerable amount of attention over recent years. However, unlike research focused on studying 5 × 5 basketball players, there is a lack of scientific literature focused on examining countermovement vertical jump (CMJ) and sprint performance characteristics of 3 × 3 athletes. Thus, the purpose of the present study was to compare force-time metrics during both eccentric and concentric phases of the CMJ and acceleration and deceleration capabilities between 3 × 3 and 5 × 5 top-tier professional male basketball athletes. Ten 3 × 3 and eleven 5 × 5 professional basketball players volunteered to participate in the present study. Upon completion of a standardized warm-up, each athlete performed three maximum-effort CMJs, followed by two 10 m sprints. A uni-axial force plate system sampling at 1,000 Hz was used to analyze CMJ force-time metrics and a radar gun sampling at 47 Hz was used to derive sprint acceleration-deceleration measures. Independent t-tests and Hedge's g were used to examine between-group statistically significant differences (p < 0.05) and effect size magnitudes. The findings of the present study reveal that 3 × 3 and 5 × 5 professional male basketball players tend to display similar neuromuscular performance characteristics as no significant differences were observed in any force-time metric during both eccentric and concentric phases of the CMJ (g = 0.061-0.468). Yet, prominent differences were found in multiple measures of sprint performance, with large effect size magnitudes (g = 1.221-1.881). Specifically, 5 × 5 basketball players displayed greater average and maximal deceleration and faster time-to-stop than their 3 × 3 counterparts. Overall, these findings provide reference values that sports practitioners can use when assessing athletes' CMJ and sprint performance capabilities as well as when developing sport-specific training regimens to mimic on-court competitive demands.

Vertical jump neuromuscular performance of professional female handball players-starters vs. non-starters comparison.

Given the complex nature of the handball as a game, players are required to possess a distinct set of physical and physiological attributes to attain peak performance. With the countermovement vertical jump (CVJ) being widely implemented as a non-invasive and time-efficient testing modality in sports settings, the purpose of the present study was twofold: (a) to establish a CVJ profile of professional female handball players and (b) to examine differences in force-time metrics between starters and non-starters. Forty-two professional female handball players (e.g., SuperLeague) volunteered to participate in this study. Each athlete performed three maximum-effort CVJs with no arm swing while standing on a uni-axial force plate system sampling at 1,000 Hz. Independent t-tests were used to examine differences in each variable between starters and non-starters. The results revealed that starters attained superior performance within the eccentric phase of the CVJ when compared to non-starters, particularly in terms of eccentric peak velocity (-0.957 ± 0.242 vs. -0.794 ± 0.177 m·s-1), eccentric mean power (320.0 ± 77.7 vs. 267.1 ± 75.2 W), and eccentric peak power (929.0 ± 388.1 vs. 684.4 ± 214.2 W). While not reaching the level of statistical significance, moderate-to-large effect sizes were observed for concentric impulse, peak velocity, and mean and peak force and power, all in favor of players included in the starting lineup (g = 0.439-0.655). Overall, these findings suggest that at the top-tier level of handball competition, the ability to secure a spot in a starting lineup may be possibly influenced by the athlete's eccentric performance capabilities. Thus, the development of lower-body eccentric strength and power may positively impact on-court athlete performance and ultimately help the team secure the desired game outcome.

Concurrent validity and test–retest reliability of VALD ForceDecks' strength, balance, and movement assessment tests

ObjectivesTo evaluate the concurrent validity and test–retest reliability of common movement, strength, and balance tests using portable uniaxial dual force plates. DesignRepeated measures cross-sectional study. MethodsSixteen healthy individuals participated in two testing sessions, where they performed 12 different movement, strength, and balance tests. Vertical ground reaction force and centre of pressure data were collected using the VALD ForceDecks simultaneously with ground-embedded laboratory force plates. Concurrent validity was assessed using root mean square error for raw time-series data and Bland–Altman plots for discrete metrics. Test–retest reliability was assessed using intraclass correlation coefficients and minimal detectable changes. ResultsForceDecks recorded vertical ground reaction forces and center of pressure with high accuracy compared to laboratory force plates. The mean bias between systems was negligible (<2 N or 0.1 mm), with small limits of agreement (<5 N or 1 mm). Overall, 530/674 (79%) showed good or excellent validity (<10% difference) and 611/773 (79%) had good or excellent reliability (intraclass correlation coefficient >0.75). ForceDecks reliability was similar to laboratory force plates (<0.07 intraclass correlation coefficient median difference for all metrics). ConclusionsPortable uniaxial force plates record highly accurate vertical ground reaction forces and center of pressure during a range of movement, strength, and balance tests. The VALD ForcDecks are a valid and reliable alternative to laboratory force plates when strict standardized testing and data analysis procedures are followed. Users should be aware of the validity and reliability characteristics of the tests and metrics they choose.

Research on the Influence of Humidity on the Manufacture of GFRP Vessels in the Equatorial

The objective of this research work is to analyze the behavior between fiberglass laminate under tensile tests, assembled under different humidity conditions. For which specimens were designed under the regime of the international standard ASTM D3039; which took an assembly process within a controlled environment; the design variables used were relative humidity and curing time. Subsequently, the traction-displacement behavior was checked under a uniaxial force, obtaining the maximum take-off force. In addition, Simpson numerical integration was applied to calculate elastic energy. Obtaining that the relative humidity and the days of curing influence the chemical and mechanical properties of the material. Se shows that the percentage of humidity recommended for assembling laminates in GRP is 66% since it has greater elastic energy and take-off force. Finally, it is concluded that to have a high resistance in the material at least 7 days of curing of the epoxy resin must be applied.

Starters vs. non-starters differences in vertical jump force-time metrics in female professional volleyball players.

As one of the fundamental volleyball skills, countermovement vertical jump (CMJ) has been commonly implemented in the applied sports setting as a non-invasive and time-efficient assessment of athletes' lower-body neuromuscular function. The purpose of the present study was to examine the differences in CMJ characteristics between starters and non-starters within a cohort of professional female volleyball players. Nineteen athletes competing in one of the top European leagues (i.e., SuperLeague) volunteered to participate in the present investigation. Following the completion of a warm-up protocol, each athlete performed three maximal-effort CMJs with no arm swing while standing on a uni-axial force plate system sampling at 1,000 Hz. The following force-time metrics were used for performance analysis purposes: braking phase duration and impulse, eccentric and concentric duration, mean and peak force and power, contraction time, jump height, and reactive strength index-modified. Mann-Whitney U and independent t-tests revealed no statistically significant differences (p > 0.05) during both eccentric and concentric phases of CMJ between the players included in the starting lineup (n = 9) and their substitutions (n = 10), with the effect sizes being small to moderate in magnitude (g = 0.053-0.683). While further research is warranted on this topic, these results suggest that securing a position in a starting lineup at the professional level of volleyball play may be more contingent on the player's ability to proficiently execute sport-specific skills (e.g., blocking, attacking), rather than the performance on the CMJ assessment, considering that the observed values for both groups fall within the desired ranges for this specific population of athletes.

Hypergravity-exacerbated cracking in high-speed rotating 7075 aluminum blades

On Earth, high-speed rotating blades and rotors experience hypergravity, which is mainly derived from centrifugal force. Aluminum alloys are widely used in high-speed rotating machines. In particular, 7075 aluminum has excellent properties, providing it with great potential for application in high-temperature rotating parts. In this work, the cracking behavior and microstructural evolution characteristics of high-speed rotating blades under different stresses were studied. A specifically designed instrument and blades with multiple necks were assembled, and the stress was tuned by adding weight to the blade tip. Each rotating blade cracked on its root neck, indicating that the gradient hypergravitational force decreased from the root to the tip. The degree of high-temperature cracking obviously increased with a sawtooth-like tip, but the degree of low-temperature cracking did not obviously increase with a smooth tip. A comparison under a constant uniaxial force required a greatly increased ultimate cracking strength that was approximately 10–18 times greater than that under hypergravitational force at the same temperature. Force analysis indicated that the coupling of hypergravitational forces in the normal direction and torsional forces in the tangential direction accelerated cracking. A uniaxial force caused grains to extend along the blade direction. However, a tangential force cut these extended grains to accelerate cracking and grain refining. In this study, real-world simulated service conditions for commercial alloys rotating at high speeds and a new understanding of the mechanical properties of alloys under various severe conditions were provided.