Dynamic Strength Test Research Articles

Experience in ensuring the strength of the supporting structures of locomotives and electric multiple units

To ensure fatigue strength of metal structures in mechanical engineering, various approaches are practiced. One of them allows for the appearance of cyclic stresses in details with amplitudes exceeding the fatigue limit. Typically, this approach is justified where the loads are fairly regular and ample opportunities for fatigue testing exists, but the requirement of a minimum metal consumption is critically important as well. Another approach to ensuring fatigue strength does not allow the possibility of cyclic stresses with amplitudes exceeding its endurance limit in the designed structure. With regard to the supporting elements of locomotives and electric multiple units (EMU) to ensure the fatigue resistance characteristics in Russia and the CIS countries, the second of these approaches has been implemented and successfully practiced for many years. Its purpose is to ensure the absence of fatigue damage in the parts of the carriage and the body during the designated service life. Relevant requirements for strength and dynamic qualities for these types of rolling stock, as well as the method of conducting dynamic strength tests are currently formalized in the standards. The article presents the main provisions of the methodology currently used on the railways of the Russian Federation and CIS countries to control the strength requirements of load-bearing structures of locomotives and EMUs, as well as the admission of these types of rolling stock to operation. Types of dynamic strength tests are described, strength indicators are listed, methods for their determination are indicated. Today, this technique successfully solves the problem of the strength of load-bearing structures of traction rolling stock.

Investigation on very high cycle fatigue of PA66-GF30 GFRP based on fiber orientation

The purpose of this study is to evaluate the effects of glass fiber (GF) of PA66-GF30 orientation on very high cycle fatigue (HVCF) life and also to develop an optimized test apparatus such as measurement of dynamic elastic modulus and design of test specimens. Dynamic elastic modulus, tensile strength and fatigue strength tests were conducted at room temperature based on GF orientation (0°, 45°, 90°). Conventional fatigue (3 Hz) and ultrasonic fatigue (20 kHz) tests were performed at the same stress ratio (R = −1). Fracture surface observation showed that GF 0° exhibited a higher fatigue strength in comparison with GF 45 and 90°. Various defects such as voids and microcracks to the load direction around the GF end or debonding in glass fiber reinforced plastic (GFRP) and the slope change in very long life regime of S–N diagram.

Load-Velocity Relationship in National Paralympic Powerlifters: A Case Study.

To examine the relationships between different loading intensities and movement velocities in the bench-press exercise (BP) in Paralympic powerlifters. A total of 17 national Paralympic powerlifters performed maximum dynamic strength tests to determine their BP 1-repetition maximum (1RM) in a Smith-machine device. A linear position transducer was used to measure movement velocity over a comprehensive range of loads. Linear-regression analysis was performed to establish the relationships between the different bar velocities and the distinct percentages of 1RM. Overall, the correlations between bar velocities and %1RM were strong over the entire range of loads (R2 .80-.91), but the precision of the predictive equations (expressed as mean differences [%] between actual and predicted 1RM values) were higher at heavier loading intensities (∼20% for loads ≤70% 1RM and ∼5% for loads ≥70% 1RM). In addition, it seems that these very strong athletes (eg,1RM relative in the BP = 2.22 [0.36]kg·kg-1, for male participants) perform BP 1RM assessments at lower velocities than those previously reported in the literature. The load-velocity relationship was strong and consistent in Paralympic powerlifters, especially at higher loads (≥70% 1RM). Therefore, Paralympic coaches can use the predictive equations and the reference values provided here to determine and monitor the BP loading intensity in national Paralympic powerlifters.

Effects of inhibitor KCl on shale expansibility and mechanical properties

Abstract The expansibility and mechanical properties of shale are significantly influenced by water-based muds (WBMs); thus, it is necessary to mitigate this effect to avoid borehole instabilities in drilling operation. Potassium chloride (KCl) is usually used as inhibitor to reduce hydration of shales. In this study, we investigated the inhibitory efficiency of KCl on shale through a series of experiments, including dynamic linear swelling (DLS) tests and uniaxial compressive strength (UCS) tests, to provide reference for the design of WBMs. These tests were conducted on shale samples soaked in KCl solution for 24, 48, 72, and 96 h with saline concentrations of 0%, 2%, 4%, 6%, and 8%. Experimental results show that samples with microcracks and bedding fissures have the highest swelling increase and the largest strength reduction after immersion in solution. The swelling potential decreased with increasing KCl concentration. In addition, KCl exhibited a certain inhibitory effect on the weakening of the mechanical properties of samples. An increase in the KCl concentration increases the compressive strength and elastic modulus, and decreases the Poisson's ratio. However, in terms of homogeneous samples, the UCS test results show that exposure to water is weakly related to weakening of the mechanical properties of shale samples. We found that immersing the shale in KCl solution for a longer time decreases the compressive strength, increases the Poisson's ratio, and decreases the elastic modulus.

Rock Failure Analysis under Dynamic Loading Based on a Micromechanical Damage Model

A micromechanical constitutive damage model accounting for micro-crack interactions was developed for brittle failure of rock materials under compressive dynamic loading. The proposed model incorporates pre-existing flaws and micro-cracks that have same size with specific orientation. Frictional sliding on micro-cracks leading to inelastic deformation is very influential mechanism resulting in damage occurrence due to nucleation of wing-crack from both sides of pre-existing micro-cracks. Several homogenization schemes including dilute, Mori-Tanaka, self-consistence, Ponte-Castandea & Willis are usually implemented for up-scaling of micro-cracks interactions. In this study the Self-Consistent homogenization Scheme (SCS) was used in the developed damage model in which each micro-crack inside the elliptical inclusion surrounded by homogenized matrix experiences a stress field different from that acts on isolated cracks. Therefore, the difference between global stresses acting on rock material and local stresses experienced by micro-crack inside inclusion yields stress intensity factor (SIF) at the cracks tips which are utilized in the formulation of the dynamic crack growth criterion. Also the damage parameter was defined in term of crack density parameter. The developed model was programmed and used as a separate and new constitutive model in the commercial finite difference software (FLAC). The dynamic uniaxial compressive strength test of a brittle rock was simulated numerically and the simulated stress-strain curves under different imposed strain rates were compared each other. The analysis results show a very good strain rate dependency especially in peak and post-elastic region. The proposed model predicts a macroscopic stress-strain relation and a peak stress (compressive strength) with an associated transition strain rate beyond which the compressive strength of the material becomes highly strain rate sensitive. Also the damage growth process was studied by using the proposed micromechanical damage model and scale law was plotted to distinguish the dynamic and quasi-dynamic loading boundary. Results also show that as the applied strain rate increases, the simulated peak strength increases and the damage evolution becomes slower with strain increment.

Microwave absorbing and mechanical properties of carbon fiber/bismaleimide composites imbedded with Fe@C/PEK-C nano-membranes

An effective approach is proposed to fabricate hybrid multilayer stealth composite composed of carbon fiber/bismaleimide composites containing carbon coated Fe (Fe@C)/phenolphthalein polyetherketone (PEK-C) nano-membranes as interlaminar electromagnetic absorbing agents. Dynamic mechanical analysis and interlaminar shear strength tests were carried out to evaluate mechanical properties. Special attention was paid to the permittivity, permeability and microwave absorbing properties. The results indicated that the radar-absorbing structural materials (RASs) showed a minimum reflection loss (RL) value of − 16.85 dB observed at 11.5 GHz at a thickness of 1.7 mm, with the values exceeding − 10 dB achieved in 9.7–16.7 GHz with increasing thicknesses. The measured RL values were in good agreement with the calculated ones. This strategy may be extended as a versatile approach to achieve high performance RASs, thereby promoting their engineering applications at low cost in aerospace industry.

Preliminary Investigation Into the Effect of ACTN3 and ACE Polymorphisms on Muscle and Performance Characteristics.

Wagle, JP, Carroll, KM, Cunanan, AJ, Wetmore, A, Taber, CB, DeWeese, BH, Sato, K, Stuart, CA, and Stone, MH. Preliminary investigation into the effect of ACTN3 and ACE polymorphisms on muscle and performance characteristics. J Strength Cond Res 35(3): 688-694, 2021-The purpose of this investigation was to explore the phenotypic and performance outcomes associated with ACTN3 and ACE polymorphisms. Ten trained men (age = 25.8 ± 3.0 years, height = 183.3 ± 4.1 cm, body mass = 92.3 ± 9.3 kg, and back squat to body mass ratio = 1.8 ± 0.3) participated. Blood samples were analyzed to determine ACTN3 and ACE polymorphisms. Standing ultrasonography images of the vastus lateralis (VL) were collected to determine whole muscle cross-sectional area (CSA-M), and a percutaneous muscle biopsy of the VL was collected to determine type I-specific CSA (CSA-T1), type II-specific CSA (CSA-T2), and type II to type I CSA ratio (CSA-R). Isometric squats were performed on force platforms with data used to determine peak force (IPF), allometrically scaled peak force (IPFa), and rate of force development (RFD) at various timepoints. One repetition maximum back squats were performed, whereby allometrically scaled dynamic strength (DSa) was determined. Cohen's d effect sizes revealed ACTN3 RR and ACE DD tended to result in greater CSA-M but differ in how they contribute to performance. ACTN3 RR's influence seems to be in the type II fibers, altering maximal strength, and ACE DD may influence RFD capabilities through a favorable CSA-R. Although the findings of the current investigation are limited by the sample size, the findings demonstrate the potential influence of ACTN3 and ACE polymorphisms on isometric and dynamic strength testing. This study may serve as a framework to generate hypotheses regarding the effect of genetics on performance.

Acute effects of aerobic exercise performed with different volumes on strength performance and neuromuscular parameters

The aim of the present study was to investigate the acute effect of the aerobic exercise volume on maximum strength and strength-endurance performance; and possible causes of strength decrements (i.e. central and peripheral fatigue). Twenty-one moderately trained men were submitted to a maximal incremental test to determine anaerobic threshold (AnT) and maximum dynamic strength (1RM) and strength-endurance (i.e. total volume load [TV]) tests to determine their baseline strength performance. Following, subjects performed six experimental sessions: aerobic exercise sessions (continuous running at 90% AnT) with different volumes (3 km, 5 km or 7 km) followed by 1RM or strength-endurance test in the 45° leg press exercise. Maximum voluntary isometric contraction (MVIC), voluntary activation (VA) level, contractile properties, and electromyographic activity (root mean square [RMS]) of the knee extensor muscles were assessed before and after aerobic exercises and after strength tests. TV was lower after 5 km and 7 km runs than in the control condition (12% and 22%, respectively). Additionally, TV was lower after 7 km than 3 km (14%) and 5 km (12%) runs. MVIC, VA, RMS, and contractile properties were reduced after all aerobic exercise volumes (∼8%, ∼5%, ∼11% and ∼6–14%, respectively). Additionally, MVIC, VA, and contractile properties were lower after strength tests (∼15%, ∼6%, ∼9–26%, respectively). In conclusion, strength-endurance performance is impaired when performed after aerobic exercise and the magnitude of this interference is dependent on the aerobic exercise volume; and peripheral and central fatigue indices could not explain the different TV observed.

Effects of strength training on bioenergetics parameters determined at velocity corresponding to maximal oxygen uptake in endurance runners

Summary Objectives The present study analyzes the impact of a strength training program on bioenergetics parameters determined at velocity corresponding to maximal oxygen uptake ( v V ˙ O 2 max ). Methods Sixteen recreational long-distance runners were divided into strength training (STG, n = 9) and control (CG, n = 7) groups. Before and after 8 weeks, the volunteers performed: maximal incremental treadmill test, constant-speed running at pre-training v V ˙ O 2 max , and maximum dynamic strength test (1RM). Energy cost of running (ECr), and aerobic (AMET) and anaerobic (ANMET) metabolism contributions were estimated at v V ˙ O 2 max . Results No differences were observed at baseline between groups (P > 0.05). After experimental period, there was an increase in 1RM for STG (27 ± 18%, P = 0.008), but not for CG (P > 0.05). The changes in ECr (pre = 0.254 ± 0.038 vs. post = 0.255 ± 0.037 kJ·m−1), AMET (pre = 191.5 ± 26.2 vs. post = 193.0 ± 31.7 kJ), and ANMET (pre = 20.9 ± 6.4 vs. post = 21.0 ± 5.7 kJ) were not significant different (P > 0.05) to STG; as well as to CG (ECr - pre = 0.260 ± 0.046 vs. post = 0.259 ± 0.034 kJ·m−1, AMET - pre = 209.7 ± 30.2 vs. post = 203.3 ± 26.6 kJ, and ANMET - pre = 19.3 ± 6.4 vs. post = 23.9 ± 4.6 kJ). Conclusions These findings suggest that 8 weeks strength training improved the maximum dynamic strength and did not alter bioenergetics parameters measured at v V ˙ O 2 max in recreational endurance runners.

The effects of functional and traditional strength training on different strength parameters of elderly women: a randomized and controlled trial.

Physical exercise is the main strategy for improving physical fitness in elderly population. However, it is not clear which training method lead to greater adaptations on maximal dynamic strength, muscle power, muscle endurance and isometric strength in this population. Thus, our aim was to compare the effects of functional and traditional training on these variables in the elderly. This study lasted twelve weeks, where 44 elderly women were randomly divided into three groups: functional training (FT; N.=18), traditional training (TT; N.=15), and control group (CG; N.=11). Maximal dynamic strength and muscle power tests were performed in pushing (Chest Press), pulling (Seated Row), and squatting (Leg Press 45°) actions. In addition, isometric strength with hand grip test (HG) and isometric dead lift test (ID) and muscle endurance with 30-s chair stand (CS) and 30-s arm curl (AC) tests were used. Both experimental groups improved significantly in strength (FT: Chest Press 24.9%, Leg Press 45° 38.4%, Seated Row 21.6%; TT: Chest Press 27.6%, Leg Press 45° 40.9%, Seated Row 24.5%), power (FT: Chest Press 13.6%, Leg Press 45° 11.6%, Seated Row 13.6%; TT: Chest Press 18.2%, Leg Press 45° 9.8%, Seated Row 19.2%) isometric strength (FT: HG=14.7%, ID=13.6%; TT: HG=19.1%), and endurance (TF: CS=19.6%, AC=23.8%; TT: AC=15.5%) with P≤0.05, except TT in ID (4.4%) and SL (4.6%). There was no difference between experimental groups; however, both experimental groups were statistically superior to CG. Both training protocols were equally effective in improving different strength manifestations in the elderly.

Effect of addition graphene to ethylene vinyl acetate and low‐density polyethylene

Graphene (Gr) distribution in low‐density polyethylene (LDPE) and ethylene vinyl acetate (EVA) considerably increased thermal stability and mechanical properties of LDPE/Gr or EVA/Gr composites. Dynamic mechanical analysis (DMA) and strength testing machine were used to study mechanical properties. The high specific surface areas and superior properties of Gr improved thermal strength, storage modulus, and mechanical properties of composites. Outstanding distribution of Grs was accomplished and verified by atomic force microscopy. LDPE/Gr and EVA/Gr composites were characterized by transmission electron microscope (TEM), X‐ray diffraction, and thermogravimetric analyses to study the distribution morphology and thermal strength. Results display that the presence of filler does not create an alteration in the microscopic structure of polymers. Measurement of tensile properties shows that the tensile strength of composites contains Gr is significantly higher than similar values for pure EVA and LDPE. The DMA shows that the storage modulus of composites is much greater than that of pure EVA and LDPE. The thermal stability of the composite contains Gr is also considerably higher than that of pure EVA and LDPE. J. VINYL ADDIT. TECHNOL., 24:E177–E185, 2018. © 2018 Society of Plastics Engineers

Методика обработки экспериментальных данных ходовых и динамико-прочностных испытаний

Методика обработки экспериментальных данных ходовых и динамико-прочностных испытаний

ANALYSIS ON THE RELATION BETWEEN VELOCITY AND POWER VALUES DURING PROPULSIVE PHASE OF BENCH THROW EXERCISE AND UPPER-BODY STRENGTH CHARACTERISTICS IN PROFESSIONAL HANDBALL PLAYERS

The purpose of this study is to analyze the relation between velocity and power values during propulsive phase of bench throw exercise and upper-body strength characteristics in professional handball players and to determine whether upper-body strength characteristics have a significant effect on velocity and power parameters. In accordance with this purpose, a total of 13 professional handball players competing in Turkish Handball 1. League (age: 25.4 ± 3.86 years; height: 187.5 ± 8.33 cm; body weight: 90.9 ± 14.8 kg) voluntarily participated in the research. In this study, maximal dynamic strength test was applied in bench press (BP) exercises in addition to the right and left hand grip strength test with the purpose of determining the upper-body strength characteristics. In order to determine velocity and power parameters, bench throw (BT) exercises were applied by using an external load that corresponds to 30% of body weights of the participants via an isoinertial velocity converter (T-Force dynamic measurement system) and values of mean propulsive velocity (MPV), peak velocity (PV), mean propulsive power (MPP) and peak power (PP) were obtained. Descriptive statistics, Spearman correlation analysis and Kolmogorov-Smirnov normality tests were used in order to analyze data. According to analysis results, while mean one-repetition maximal (1RM) strength values of the participants in BP exercise were obtained as 97.8 (± 15.0 kg), their right and left hand grip strength values were respectively obtained according to the order specified as 55.4 (± 8.16 kg) and 53.7 (± 5.81 kg). It has been concluded that while there is a statistically positive and significant relation between the MPV (r = .674, p 0.05, respectively) and PP values (r = .487; r = .401, p> 0.05, respectively). It has also been concluded that there is a statistically positive and highly significant relation between 1RM strength values in BP exercises of the participants and MPV (r = .728), PV (r = .775), MPP (r = .703) and PP (r = .759) values obtained during the propulsive phase of BT exercises (p < 0.01). As a result, it can be suggested that upper-body strength characteristic positively affects velocity and power parameters, velocity and power characteristics are dominant and provide a significant contribution to the performance and these results will contribute to trainers and conditioners while preparing training programs in sports branches. Article visualizations:

The CRH-Transgenic Cushingoid Mouse Is a Model of Glucocorticoid-Induced Osteoporosis.

ABSTRACTGlucocorticoids (GCs) have unparalleled anti‐inflammatory and immunosuppressive properties, which accounts for their widespread prescription and use. Unfortunately, a limitation to GC therapy is a wide range of negative side effects including Cushing's syndrome, a disease characterized by metabolic abnormalities including muscle wasting and osteoporosis. GC‐induced osteoporosis occurs in 30% to 50% of patients on GC therapy and thus, represents an important area of study. Herein, we characterize the molecular and physiologic effects of GC‐induced osteoporosis using the Cushing's mouse model, the corticotropin releasing hormone (CRH) transgenic mouse (CRH‐Tg). The humeri, femurs, and tibias from wild‐type (WT) and CRH‐Tg male mice, aged 13 to 14 weeks old were subjected to multiple bone tests including, micro–computed tomography (μCT), static and dynamic histomorphometry, strength testing, and gene expression analyses. The CRH‐Tg mice had a 38% decrease in cortical bone area, a 35% decrease in cortical thickness, a 16% decrease in trabecular thickness, a sixfold increase in bone adiposity, a 27% reduction in osteoid width, a 75% increase in bone‐resorbing osteoclast number/bone surface, a 34% decrease in bone formation rate, and a 40% decrease in bone strength compared to WT mice. At the gene expression level, CRH‐Tg bone showed significantly increased osteoclast markers and decreased osteoblast markers, whereas CRH‐Tg muscle had increased muscle atrophy gene markers compared to WT mice. Overall, the CRH‐Tg mouse model aged to 14 weeks recapitulated many features of osteoporosis in Cushing's syndrome and thus, represents a useful model to study GC‐induced osteoporosis and interventions that target the effects of GCs on the skeleton. © 2017 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Optimization of thermo-mechanical performance of epoxy nanocomposites containing surface-modified graphene nanosheets using statistical analysis

Epoxy-based nanocomposites containing different concentrations (0–3%) of surface-modified graphene nanosheets (GNS) with 3-aminopropyltriethoxysilane were prepared and their thermal and mechanical properties including dynamic mechanical analysis, tensile strength, hardness, and abrasion tests were evaluated in order to have a database for thermo-mechanical properties of epoxy nanocomposites. The main aim of this study was to understand the optimum percentage of GNS which would perform the best reinforcing influence on mechanical and physical performance of an epoxy nanocomposite. The results explain how applying the analysis of variance (ANOVA) method as a useful tool in optimization of GNS concentration in preparation of high-performance epoxy-based nanocomposites.

Resistance training intensity and volume affect changes in rate of force development in resistance-trained men.

To compare the effects of two different resistance training programs, high intensity (INT) and high volume (VOL), on changes in isometric force (FRC), rate of force development (RFD), and barbell velocity during dynamic strength testing. Twenty-nine resistance-trained men were randomly assigned to either the INT (n=15, 3-5RM, 3-min rest interval) or VOL (n=14, 10-12RM, 1-min rest interval) training group for 8weeks. All participants completed a 2-week preparatory phase prior to randomization. Measures of barbell velocity, FRC, and RFD were performed before (PRE) and following (POST) the 8-week training program. Barbell velocity was determined during one-repetition maximum (1RM) testing of the squat (SQ) and bench press (BP) exercises. The isometric mid-thigh pull was used to assess FRC and RFD at specific time bands ranging from 0 to 30, 50, 90, 100, 150, 200, and 250ms. Analysis of covariance revealed significant (p<0.05) group differences in peak FRC, FRC at 30-200ms, and RFD at 50-90ms. Significant (p<0.05) changes in INT but not VOL in peak FRC (INT: 9.2±13.8%; VOL: -4.3±10.2%), FRC at 30-200ms (INT: 12.5-15.8%; VOL: -1.0 to -4.3%), and RFD at 50ms (INT: 78.0±163%; VOL: -4.1±49.6%) were observed. A trend (p=0.052) was observed for RFD at 90ms (INT: 58.5±115%; VOL: -3.5±40.1%). No group differences were observed for the observed changes in barbell velocity. Results indicate that INT is more advantageous than VOL for improving FRC and RFD, while changes in barbell velocity during dynamic strength testing are similarly improved by both protocols in resistance-trained men.

Production and Characterization of Bioplastics Obtained by Injection Moulding of Various Protein Systems

Bioplastic materials from renewable polymers, like proteins, constitute a highly interesting field for important industrial applications such as packaging, agriculture, etc., in which thermo-mechanical techniques are increasingly being used. This study assesses bioplastic materials produced by injection from blends previously prepared in a batch mixer using various protein concentrates and isolates. A mixing time of 5 min has been selected in order to ensure correct homogenous blends. A comparison between different protein-based specimens was performed by dynamic mechanical thermal analysis, tensile strength, water uptake and transmittance tests. The comparison reveals that the protein nature and the percentage of plasticizer lead to bioplastics with different properties and, consequently, different applications. Protein concentrates and isolates, wastes and surpluses from the food industry, may be useful for producing bioplastics with suitable mechanical properties and processability, as well as biodegradability, by means of suitable mixing and injection moulding conditions.

The Importance of Muscular Strength in Athletic Performance.

This review discusses previous literature that has examined the influence of muscular strength on various factors associated with athletic performance and the benefits of achieving greater muscular strength. Greater muscular strength is strongly associated with improved force-time characteristics that contribute to an athlete's overall performance. Much research supports the notion that greater muscular strength can enhance the ability to perform general sport skills such as jumping, sprinting, and change of direction tasks. Further research indicates that stronger athletes produce superior performances during sport specific tasks. Greater muscular strength allows an individual to potentiate earlier and to a greater extent, but also decreases the risk of injury. Sport scientists and practitioners may monitor an individual's strength characteristics using isometric, dynamic, and reactive strength tests and variables. Relative strength may be classified into strength deficit, strength association, or strength reserve phases. The phase an individual falls into may directly affect their level of performance or training emphasis. Based on the extant literature, it appears that there may be no substitute for greater muscular strength when it comes to improving an individual's performance across a wide range of both general and sport specific skills while simultaneously reducing their risk of injury when performing these skills. Therefore, sport scientists and practitioners should implement long-term training strategies that promote the greatest muscular strength within the required context of each sport/event. Future research should examine how force-time characteristics, general and specific sport skills, potentiation ability, and injury rates change as individuals transition from certain standards or the suggested phases of strength to another.

An Investigation Into the Relationship Between Maximum Isometric Strength and Vertical Jump Performance.

Research has demonstrated a clear relationship between dynamic strength and vertical jump (VJ) performance; however, the relationship of isometric strength and VJ performance has been studied less extensively. The aim of this study was to determine the relationship between isometric strength and performance during the squat jump (SJ) and countermovement jump (CMJ). Twenty-two male collegiate athletes (mean ± SD; age = 21.3 ± 2.9 years; height = 175.63 ± 8.23 cm; body mass = 78.06 ± 10.77 kg) performed isometric midthigh pulls (IMTPs) to assess isometric peak force (IPF), maximum rate of force development, and impulse (IMP) (I100, I200, and I300). Force-time data, collected during the VJs, were used to calculate peak velocity, peak force (PF), peak power (PP), and jump height. Absolute IMTP measures of IMP showed the strongest correlations with VJ PF (r = 0.43-0.64; p ≤ 0.05) and VJ PP (r = 0.38-0.60; p ≤ 0.05). No statistical difference was observed in CMJ height (0.33 ± 0.05 m vs. 0.36 ± 0.05 m; p = 0.19; ES = -0.29) and SJ height performance (0.29 ± 0.06 m vs. 0.33 ± 0.05 m; p = 0.14; ES = -0.34) when comparing stronger to weaker athletes. The results of this study illustrate that absolute IPF and IMP are related to VJ PF and PP but not VJ height. Because stronger athletes did not jump higher than weaker athletes, dynamic strength tests may be more practical methods of assessing the relationships between relative strength levels and dynamic performance in collegiate athletes.

Damage evolution in WC–Co after repeated dynamic compressive loading detected by eddy current testing

The failure behaviour of WC–Co hard metals with binder contents of 6 and 12wt.% was investigated under repeated dynamic loadings. The materials were consolidated by field-assisted sintering and exhibited WC grain sizes of about 200nm. Static and dynamic strength tests on a servo-hydraulic testing machine and a modified split Hopkinson pressure bar (MSHPB), respectively, resulted in compressive fracture strengths between 4370MPa and 6660MPa depending on the Co content and the applied strain rate. Moreover, the hard metal samples were repeatedly loaded in the MSHPB below their compressive strength at different stress levels, and subsequently investigated by eddy current testing after each loading step. The measured eddy current signal was dependent on the stress level and the number of impacts. Additionally, the damage of the samples was examined with the help of images from the scanning electron microscope (SEM).Static strength tests of the pre-damaged material revealed that the residual strength of WC–6Co decreases with an increasing number of impacts. In contrast, WC–12Co shows strain hardening caused by the multiple-impact loadings. The size of the fragments revealed intensified microcrack initiation.