Reduction In Peak Force Research Articles

Study on Impact Load Mitigation for High-Speed Water Entry Projectiles Using Aluminum Foam Buffering Structure

Abstract This paper investigated the fluid-solid coupling nonlinear problem of water entry by a high-speed projectile, considering cavitation, air cushion effect, and water vapor generated by the high-speed relative motion between the projectile and the fluid. To this end, a sandwich structure containing aluminum foam attached piston was studied and designed. The numerical simulation of the entry process was analyzed by LS-DYNA. The results show that the sandwich structure reduces the peak impact load. 87.47% reduction in peak force during water entry and aluminum foam has good cushioning effect.

A strain rate response and self-healing organohydrogel for use in impact-protective materials

Impact-protective materials are used in many fields owing to their excellent mechanical properties, impact resistance, and rapid responses to external stimuli. In this study, a new organohydrogel (PAIG) was designed and prepared through emulsion copolymerization by combining polymer chain segment as a skeleton and oil phase containing IHP as dynamic crosslinking points. The PAIG gel system provided a stable structure and overcame the cold flow property of impact-hardening polymers (IHP) with a tensile stress of 0.48 MPa. In addition, the introduced flexible IHP chains provided a large number of boron–oxygen dynamic bonds and hydrogen bonds, which improved both the impact resistance (the peak force reduction rate of 74 %), speed- response and the self-healing ability (with an efficiency of ca. 90 %). Impressively, PAIG can withstand cyclic twisting and bending even at −20 °C, showing its excellent freezing resistance. These properties make the PAIG promising for intelligent impact-protection applications.

Energy absorption properties of origami‐based re‐entrant honeycomb sandwich structures with CFRP subjected to low‐velocity impact

AbstractThis paper investigates a honeycomb sandwich structure that draws inspiration from the craft of origami. A specific folding pattern was applied to the honeycomb to create the origami‐based re‐entrant honeycomb (ORH), aimed at improving the energy absorption properties of the sandwich structure. The study on the energy absorption properties of structures under low‐velocity impact (LVI) utilized both experimental and numerical approaches. The energy absorption properties of the sandwich structure were examined by conducting LVI tests with different impact energy and then compared to the mechanical properties of the traditional re‐entrant honeycomb sandwich structures (TRHSS). Additionally, a refined finite element model has been established and its accuracy verified. Numerical studies were conducted to explore the effects of structural parameters on the energy absorption properties of ORH sandwich structure (ORHSS). The results show that the ORHSS exhibited a significant reduction in peak force when subjected to LVI, in contrast to the TRHSS. Furthermore, the ORHSS exhibit significant efficiency in energy absorption. Enhancing the wall thickness or folding angle can significantly improve the energy absorption properties of the ORHSS, thereby boosting the honeycomb's contribution to this process. This optimization results in an improved absorptive effect of the structure. The findings offer new recommendations for developing lightweight absorbent materials with potential applications across various industries.Highlights A novel composite sandwich structure serves as an efficient device for absorbing energy. This sandwich structure exhibits excellent cushioning and energy absorption capabilities. Changing geometric parameters can enhance the impact performance of the structure. A larger folding angle makes the core more prone to deformation. The greater the forward length of the ORH, the lower specific energy absorption (SEA) of the ORHSS.

Fast optimisation of honeycombs for impact protection

Cellular solids such as honeycombs are often used in impact protection systems. Those with precisely defined geometries allow responses to be programmed to specific functions, but can be costly to design. This article presents an analytical model for fast, parametric optimisation. The analytical model, and a numerical one, were validated against experimental data for three honeycomb variants, during compression tests to 80% engineering strain, and 1, 3 and 5 J impacts. The numerical model force readings remained within 5% of the experiments. A further verification of the analytical model, varying all parameters within the honeycomb geometry, was undertaken for 5 J and 15 J impacts. The analytical model predicted energy absorption at all displacement increments to be (on average) 3% higher than the numerical one. The limits of agreement (with 95% confidence) were between +15 and −9% of the numerical model. The analytical model provided solutions almost instantly, so was used in a demonstrative parametric optimisation study, for a 10 J impact. The input and output solutions were verified in the numerical model, showing a four-fold reduction in peak force (from ∼2000 to ∼500 N).

Experimental study of solid-liquid origami composite structures with improved impact resistance

In this paper, a liquid-solid origami composite design is proposed for the improvement of impact resistance. Employing this design strategy, Kresling origami composite structures with different fillings were designed and fabricated, namely air, water, and shear thickening fluid (STF). Quasi-static compression and drop-weight impact experiments were carried out to compare and reveal the static and dynamic mechanical behavior of these structures. The results from drop-weight impact experiments demonstrated that the solid-liquid Kresling origami composite structures exhibited superior yield strength and reduced peak force when compared to their empty counterparts. Notably, the Kresling origami structures filled with STF exhibited significantly heightened yield strength and reduced peak force. For example, at an impact velocity of 3 m/s, the yield strength of single-layer STF-filled Kresling origami structures increased by 772.7% and the peak force decreased by 68.6%. This liquid-solid origami composite design holds the potential to advance the application of origami structures in critical areas such as aerospace, intelligent protection and other important fields. The demonstrated improvements in impact resistance underscore the practical viability of this approach in enhancing structural performance for a range of applications.

In silico and in vitro models reveal the molecular mechanisms of hypocontractility caused by TPM1 M8R.

Dilated cardiomyopathy (DCM) is an inherited disorder often leading to severe heart failure. Linkage studies in affected families have revealed hundreds of different mutations that can cause DCM, with most occurring in genes associated with the cardiac sarcomere. We have developed an investigational pipeline for discovering mechanistic genotype-phenotype relationships in DCM and here apply it to the DCM-linked tropomyosin mutation TPM1 M8R. Atomistic simulations predict that M8R increases flexibility of the tropomyosin chain and enhances affinity for the blocked or inactive state of tropomyosin on actin. Applying these molecular effects to a Markov model of the cardiac thin filament reproduced the shifts in Ca2+sensitivity, maximum force, and a qualitative drop in cooperativity that were observed in an in vitro system containing TPM1 M8R. The model was then used to simulate the impact of M8R expression on twitch contractions of intact cardiac muscle, predicting that M8R would reduce peak force and duration of contraction in a dose-dependent manner. To evaluate this prediction, TPM1 M8R was expressed via adenovirus in human engineered heart tissues and isometric twitch force was observed. The mutant tissues manifested depressed contractility and twitch duration that agreed in detail with model predictions. Additional exploratory simulations suggest that M8R-mediated alterations in tropomyosin-actin interactions contribute more potently than tropomyosin chain stiffness to cardiac twitch dysfunction, and presumably to the ultimate manifestation of DCM. This study is an example of the growing potential for successful in silico prediction of mutation pathogenicity for inherited cardiac muscle disorders.

Unilateral and Bilateral Isokinetic Leg Extensions Exhibit No Differences in Neuromuscular Excitation Under Maximal and Fatiguing Conditions.

Abstract Anders, JPV, Neltner, TJ, Smith, RW, Arnett, JE, Housh, TJ, Schmidt, RJ, and Johnson, GO. Unilateral and bilateral isokinetic leg extensions exhibit no differences in neuromuscular activation under maximal and fatiguing conditions. J Strength Cond Res 38(3): 474–480, 2024—The bilateral deficit is a phenomenon where force production during a bilateral (BL) muscle action is less than the sum of force produced when the muscle action is performed unilaterally (UL) with both limbs. The purpose of this study was to compare peak force, electromyographic (EMG) amplitude (AMP), and mean power frequency (MPF) of the nondominant leg between UL and BL isokinetic leg extensions. Eleven recreationally trained men (mean ± SD; age = 20.8 ± 1.7 years; body mass = 84.0 ± 16.2 kg; height = 179.3 ± 7.2 cm) volunteered to participate in this study. The 2 test visits included UL and BL maximal isokinetic leg extensions at 180°·second−1 followed by a fatiguing task of either 50 UL or 25 UL followed immediately by 25 BL (ULBL) maximal, isokinetic leg extensions at 180°·second−1, in random order on separate days. The results demonstrated a significant (p = 0.015, = 0.460) bilateral deficit in force (UL = 56.29 ± 11.20 kg; BL = 50.32 ± 7.35 kg; d = 0.63; 95% CI [1.42, 10.52]) but no significant bilateral deficit in EMG AMP (p = 0.892, = 0.002). The peak force during the fatiguing task demonstrated a significant main effect for repetition (p < 0.001, = 0.943) characterized by a reduced peak force from repetitions 20–50. Similarly, EMG MPF demonstrated a significant main effect for repetition (p < 0.001, = 0.702) characterized by a reduced EMG MPF from repetitions 35–50. There were no significant effects (p = 0.102–0.387, = 0.096–0.203) for EMG AMP. These findings suggested that the bilateral deficit was not associated with a neuromuscular deficit and UL muscle actions may be used to potentiate force production of subsequent BL muscle actions.

Mechanical testing and comparison of porcine tissue, silicones and 3D-printed materials for cardiovascular phantoms.

Background: Cardiovascular phantoms for patient education, pre-operative planning, surgical training, haemodynamic simulation, and device testing may help improve patient care. However, currently used materials may have different mechanical properties compared to biological tissue. Methods/Aim: The aim of this study was to investigate the mechanical properties of 3D-printing and silicone materials in comparison to biological cardiovascular tissues. Uniaxial cyclic tension testing was performed using dumbbell samples from porcine tissue (aorta, pulmonary artery, right and left ventricle). Flexible testing materials included 15 silicone (mixtures) and three 3D-printing materials. The modulus of elasticity was calculated for different deformation ranges. Results: The modulus of elasticity (0%-60%) for the aorta ranged from 0.16 to 0.18N/mm2, for the pulmonary artery from 0.07 to 0.09N/mm2, and for the right ventricle as well as the left ventricle short-axis from 0.1 to 0.16N/mm2. For silicones the range of modulus of elasticity was 0.02-1.16N/mm2, and for the 3D-printed materials from 0.85 to 1.02N/mm2. The stress-strain curves of all tissues showed a non-linear behaviour in the cyclic tensile testing, with a distinct toe region, followed by exponential strain hardening behaviour towards the peak elongation. The vessel samples showed a more linear behaviour comparted to myocardial samples. The silicones and 3D printing materials exhibited near-linearity at higher strain ranges, with a decrease in stiffness following the initial deformation. All samples showed a deviation between the loading and unloading curves (hysteresis), and a reduction in peak force over the first few cycles (adaptation effect) at constant deformation. Conclusion: The modulus of elasticity of silicone mixtures is more in agreement to porcine cardiovascular tissues than 3D-printed materials. All synthetic materials showed an almost linear behaviour in the mechanical testing compared to the non-linear behaviour of the biological tissues, probably due to fibre recruitment mechanism in the latter.

Kinetics of Depth Jumps Performed by Female and Male National Collegiate Athletics Association Basketball Athletes and Young Adults.

The depth jump (DJ) is commonly used to evaluate athletic ability, and has further application in rehabilitation and injury prevention. There is limited research exploring sex-based differences in DJ ground reaction force (GRF) measures. This study aimed to evaluate for sex-based differences in DJ GRF measures and determine sample size thresholds for binary classification of sex. Forty-seven participants from mixed-sex samples of NCAA athletes and young adults performed DJs from various drop heights. Force platform dynamometry and 2-dimensional videography were used to estimate GRF measures. Three-way mixed analysis of variance was used to evaluate main effects and interactions. Receiver operating characteristic (ROC) curve analysis was used to evaluate the combined sensitivity and specificity of dependent measures to sex. Results revealed that reactive strength index scores and rebound jump heights were greater in males than females (p < 0.001). Additionally, young adult females showed greater peak force reduction than young adult males (p = 0.002). ROC curve analysis revealed mixed results that appeared to be influenced by population characteristics and drop height. In conclusion, sex-based differences in DJ performance were observed, and the results of this study provide direction for future DJ investigations.

Indentation and impact response of conventional, auxetic, and shear thickening gel infused auxetic closed cell foam

Auxetic closed cell foams, and highly viscoelastic foams, both show potential to improve impact protection. Specifically, auxetics adapt to the shape of impacting bodies, while highly viscoelastic foams stiffen during severe impacts. So, we made auxetic closed cell foam sheets, including those that were infused with (highly viscoelastic) shear thickening gel (STG). We then undertook comparative quasistatic and impact (drop) tests. Quasistatic tests included compression, tension and indentation. Impact tests were with a flat faced impactor at energies of 1, 3 and 5 J, and a 50 mm diameter hemisphere at 1 and 3 J. Poisson’s ratios of the foams were obtained by optical full field strain measurement. An analytical model was used to separate the contribution of the various measured orthotropic properties during the hemispherical impact and indentation tests. The Poisson’s ratios of the converted foams (both with and without STG) were close to zero or marginally negative when measured through thickness. Planar values of Poisson’s ratio (measured in tension) were as low as −0.6. Through thickness Young’s moduli of the converted foams were 0.5 MPa, and planar moduli were ∼12 times higher. The auxetic foams outperformed the unconverted ones during the more severe impacts, exhibiting about half the peak force during the 3 J hemispherical impacts (2.5 vs. 5 kN). The reduction in peak force was related to a measured doubling in indentation resistance for the auxetic foam. The analytical model suggests that 7%–15% of the measured doubling in indentation resistance was due to (negative) Poisson’s ratio. Infusing the auxetic foams with STG caused, at best, a marginal reduction in peak impact force, attributed to low and non-uniform levels of infusion.

On the potential of pupil size as a metric of physical fatigue during a repeated handle push/pull task

Force output and muscle activity represent the gold standards for measuring physical fatigue. This study explores using ocular metrics for tracking changes in physical fatigue during the completion of a repeated handle push/pull task. Participants completed this task over three trials, and pupil size was recorded by means of a head-mounted eye-tracker. Blink frequency was also measured. Force impulse and maximum peak force were used as ground-truth measures of physical fatigue. As expected, a reduction in peak force and impulse was observed over time as participants became more fatigued. More interestingly, pupil size was also found to decrease from trial 1 through trial 3. No changes in blink rate were found with increasing physical fatigue. While exploratory in nature, these findings add to the sparse literature exploring the use of ocular metrics in Ergonomics. They also advance the use of pupil size as a possible future alternative for physical fatigue detection.

Study of effect of provision of cut-outs on axial collapse behaviour of circular aluminium tubes

Geometrical modification of thin-walled tubular structure is one of the innovative ways in the development for vehicle safety design. This research is developed in accordance with the need of investigation on behaviour of tubular structures with geometrical modifications like cut-outs under dynamic loading technique. Diamond and elliptical cut-out shapes are provided in multiple number arranged circumferentially in a single row on a tube surface. Tubes with cut-outs are loaded axially at three different velocities, corresponding to three different strain rates. Energy absorption characteristics like energy efficiency, specific energy absorption, peak collapse force, mean collapse force and efficiency of peak force reduction at the initiation of tube deformation are calculated and compared using finite element (FE) based ABAQUS/Explicit® software. Split-Hopkinson Pressure Bar (SHPB) is modelled in the FE software to understand the material behaviour under high strain dynamic loading. Johnson-Cook material model parameters are incorporated in the study to understand the strain rate sensitive behaviour of aluminium alloy material. Results revealed that providing diamond and elliptical cut-outs on tube is much efficient than providing circular cut-outs on tube, in terms of percentage peak load reduction as well as energy efficiency of structure. It was observed that number of cut-outs influences the polygonal deformation pattern of tube with cut-outs. Overall study significantly helps to achieve the aim of improving vehicle crashworthiness characteristics by implementing cut-outs in a crash frame.

Effects of lower limb muscle fatigue on countermovement jump, dynamic balance performance and perceived stability among elite youth netball players with chronic ankle instability

Abstract Study aim: This study aimed to investigate the effects of lower limb muscle fatigue on jumping performance, balance, and perceived stability in elite youth netball players with chronic ankle instability (CAI). Material and methods: A total of 36 elite youth netball players were recruited from National Sports Schools using purposive sampling. The severity of functional ankle instability was assessed using the Cumberland Ankle Instability Tool. Jumping performance and dynamic balance were measured using a force plate and the Y Balance Test, respectively. The experimental protocol involved a submaximal countermovement jump (CMJ) attempt followed by a fatigue protocol consisting of consecutive maximal bilateral CMJs. Statistical analysis was performed using IBM SPSS statistical software. Results: The study found no significant effect on peak velocity but a significant reduction in peak force, peak power, flight time, and jump height after completing the fatigue protocol. Post-hoc comparisons showed significant reductions in peak force, power, flight time, and jump height before the stretch-shortening cycle (SSC) protocol compared to values after 5 and 10 minutes of the SSC protocol (post-5 and post-10 SSC). Conclusion: The study results suggest that fatigue is a risk factor for sports injuries, particularly in the ankle during jumping performance, and that fatigue does not contribute to dynamic stability.

Modulation of cortical beta oscillations influences motor vigor: A rhythmic TMS-EEG study.

Previous electro- or magnetoencephalography (Electro/Magneto EncephaloGraphic; E/MEG) studies using a correlative approach have shown that β (13-30 Hz) oscillations emerging in the primary motor cortex (M1) are implicated in regulating motor response vigor and associated with an anti-kinetic role, that is, slowness of movement. However, the functional role of M1 β oscillations in regulation of motor responses remains unclear. To address this gap, we combined EEG with rhythmic TMS (rhTMS) delivered to M1 at the β (20 Hz) frequency shortly before subjects performed an isometric ramp-and-hold finger force production task at three force levels. rhTMS is a novel approach that can modulate rhythmic patterns of neural activity. β-rhTMS over M1 induced a modulation of neural oscillations to β frequency in the sensorimotor area and reduced peak force rate during the ramp-up period relative to sham and catch trials. Interestingly, this rhTMS effect occurred only in the large force production condition. To distinguish whether the effects of rhTMS on EEG and behavior stemmed from phase-resetting by each magnetic pulse or neural entrainment by the periodicity of rhTMS, we performed a control experiment using arrhythmic TMS (arTMS). arTMS did not induce changes in EEG oscillations nor peak force rate during the rump-up period. Our results provide novel evidence that β neural oscillations emerging the sensorimotor area influence the regulation of motor response vigor. Furthermore, our findings further demonstrate that rhTMS is a promising tool for tuning neural oscillations to the target frequency.

Movement Variability and Loading Characteristics in Athletes With Athletic Groin Pain: Changes After Successful Return to Play and Compared With Uninjured Athletes.

Athletic groin pain (AGP) can lead to altered movement patterns during rapid deceleration and acceleration. However, the effect of AGP on movement variability and loading patterns during such actions remains less clear. To investigate, using a continuous lateral hurdle hop task, how movement variability and magnitude measures of 3-dimensional (3D) kinematic, kinetic, and vertical ground-reaction force (vGRF) variables are (1) affected by AGP (AGP vs uninjured controls [CON]) and (2) changed after successful rehabilitation (AGP prerehabilitation vs AGP postrehabilitation vs CON). Controlled laboratory study. A total of 36 athletes diagnosed with AGP and 36 uninjured CON athletes matched on age (18-35 years), level (subelite), and type of sports played (multidirectional field sport) performed a continuous lateral hurdle hop test that involved 10 side-to-side hops over a 15-cm hurdle. The 3D joint kinematic, kinetic, and vGRF variables (total, eccentric, and concentric; ground contact time, peak force, and impulse; and eccentric rate of force development) were examined. The AGP and CON groups were tested at baseline, and the AGP group was retested after participants successfully completed a standardized, exercise-based rehabilitation program targeting intersegmental control. There were no differences in baseline characteristics between the AGP (mean ± SD: age, 27.5 ± 4.8 years; height, 179.8 ± 6.3 cm; mass, 80.3 ± 7.1 kg) and CON (mean ± SD: age, 24.1 ± 4.5 years; height, 181.0 ± 5.8 cm; mass, 80.4 ± 8.2 kg) groups. At baseline, athletes with AGP demonstrated altered loading patterns in the vGRF (longer ground contact times, reduced peak force, and reduced rate of force development) compared with CON athletes, while no significant difference in any movement variability variables was evident. After rehabilitation, the athletes with AGP demonstrated significant changes in transverse and coronal plane hip and trunk kinematics, with no significant differences in vGRF variables compared with the CON group. The differences in baseline vGRF measures between the AGP and CON groups were no longer evident after athletes with AGP underwent rehabilitation. No differences in movement variability were evident between the AGP and CON groups, either before or after rehabilitation. Rehabilitation programs should consider targeting intersegmental hip and trunk movement patterns to positively influence loading patterns in athletes with AGP.

Improving the crashworthiness of circular tube energy absorber by introducing different Gaussian curvatures on surface

Thin-walled tubes are widely used as energy absorbers in automobile vehicles to protect the occupants during a collision. Unfortunately, too high detrimental initial peak force (IPF) generated while tube crushing causes high risk and damage to the vehicle occupants. Hence, the design of such a device is vital for achieving high energy absorption (EA) with reduced peak force. Introducing a Gaussian curvature on the tube’s wall is an efficient technique to minimize the initial peak crush force. In this connection, a new structural design solution for cylindrical tubes with different Gaussian profiles (Zero, Positive, and Negative) has been proposed to improve energy absorption characteristics with reduced peak crush force. Initially, zero Gaussian curvature tubes (simple cylindrical tubes) are numerically analyzed and validated through experimental findings to prove the efficiency of the proposed numerical model. Subsequently, positive and negative Gaussian curved tubes were analyzed numerically. Their IPCF and EA were evaluated and compared. IPCF of positive and negative curvature tubes was reduced by 20–50% and 5–10%, respectively compared to zero curvature tubes. Since the proposed tube structures are of considerable potential, they can be employed as protective systems in place of conventional tubes in vehicles.

Novel Kevlar fabric composite for multifunctional soft body armor

Besides resistance to stab and impact, good flexibility and lightweight, soft body armors are also desired to have capabilities of monitoring human physical state, maintaining body temperature, and being nonflammable. In this work, a three-coaxial-layer fabric composite with Kevlar fabric as a core protection layer, reduced graphene oxide (RGO) and nano-SiO2/shear-thickening gel (STG) as functional layers is developed with the above-mentioned features for multifunctional soft body armors. The as-prepared SiO2/STG/RGO@Kevlar (SSG@Kevlar) fabric composite has excellent electro-heating performance under a low work voltage of 5 V, an extraordinary strain sensing ability (gauge factor over 41, outstanding linearity (R2 > 0.99), a fast response (69 ms), high strain resolution (0.05%)) and an effective impact energy sensing ability. Benefited from the introduction of SiO2/STG layer, the SSG@Kevlar fabric composite also exhibits an obviously enhanced anti-impact performance (a peak force reduction of 40%) and a significantly improved knife-stab resistance (a penetration depth reduction of 12 mm), due to the shear thickening effect of STG and the yarn interaction force enhancement caused by SiO2 nanoparticles. Furthermore, the SSG@Kevlar fabric composite offers remarkable fire-resistance, no open flame and glowing observed under continuous ignition due to the dense char formed. Consequently, the SSG@Kevlar fabric composite developed is promising for multifunctional soft body armors for protecting wearers in various aspects.

Impact properties of uniaxially thermoformed auxetic foams

This work describes large strain quasi-static and impact tests of a new class of low-cost, uniaxially thermoformed, transverse isotropic auxetic foams with compression ratio ranging from 20 to 80%. A custom drop tower rig with high-speed cameras suitable for these soft porous foam materials is designed and used to perform impact tests with energy ranging from 0.38 to 1.90 J, corresponding to strain rates from 64/s to 143/s. The thermoformed foams only show auxeticity when loaded along the transverse direction to the uniaxial thermoforming compression, with Poisson's ratio V21 reaching as low as −1.5 at 20% strain and then close to 0 at large strains. The samples deform with large shear band deformations, also due to the auxeticity. The negative Poisson's ratio foams along that transverse direction also show enhanced impact energy absorption performance, with normalized peak force reduction as high as ∼40% against the pristine foam; the reduction is however 20% along the thermoforming direction. A constitutive model based on Nagy's approach is applied to describe the enhancement of dynamic stress during the impact tests compared with the quasi-static one, due to strain rate effects.

Energy absorption characteristics of aluminum sandwich panels with Shear Thickening Fluid (STF) filled 3D fabric cores under dynamic loading conditions

In this study, the energy absorption characteristics of aluminum sandwich panels with Shear Thickening Fluid (STF) filled 3D fabric cores was investigated under various loading conditions. The sandwich panel with 5-ply STF-filled 3D fabric (2Al-5STF) showed the highest absorbed energy (3.53 J) in three-point bending test. The 2Al-5STF specimen also demonstrated more resistance under ballistic impact loading than the sandwich panel with 5-ply neat 3D fabric (2Al-5Neat) such that with less average penetration depth presented the highest ballistic resistance. The dynamic compression test showed the STF helped to improve the impact absorption and compressive performance of the sandwich panels. The average peak force applied to the 2Al-5STF sandwich panel (30.5 kN) was 24.5 and 54.6% less than the 2AL-5Neat and 4Al specimens, respectively, and this sandwich panel demonstrated the highest impact absorption (peak force reduction). However, the 2Al-3STF specimen demonstrated the highest peak force reduction per unit areal density, and the 2Al-5Neat specimen demonstrated better reversibility.

Fourier analysis of vertical ground reaction forces distinguishes gait patterns in hip, knee, and ankle osteoarthritis

Purpose: Osteoarthritis (OA) of the hip, knee, and ankle are prevalent diseases associated with pain and impaired function. Gait changes in OA include altered walking speeds, stance time, step time, step length, and stride length. Vertical ground reaction force (VGRF) curves reflect spring mechanics of the leg while the lower extremity interacts with the ground. In normal conditions, the VGRF is a bimodal curve wherein two maxima are separated by a local minimum near midstance. Previous studies of VGRFs in participants with OA have demonstrated reduced peak forces in OA compared to control participants; there were significant differences between hip (HOA) and knee OA (KOA) as well as HOA and ankle OA (AOA); however, there were no statistically significant differences between the KOA and AOA participants.