Output Bar Research Articles

A 90-meter Split Hopkinson Tension–Torsion Bar: Design, Construction and First Tests

AbstractThis article describes the design, construction, and first experimental results of a 90 m-long Hopkinson bar which can perform high strain rate tests in a combined tension–torsion state. The system configuration is analogous to the classic Hopkinson bar technique, consisting of three bars: a pre-stressed bar, an input bar, and an output bar; the sample is placed between the input and output bar. The measurement is also based on the classical three-wave method, where the incident, transmitted and reflected waves are measured. Incident compression and torsional waves are simultaneously generated by the failure of a fragile element that connects the pre-stressed bar to electromechanical actuators; the indirect Hopkinson tension bar technique is exploited, where the compression wave reaches the end of the output bar without stressing the sample and is reflected as a tensile input wave. The length of the bars is designed so that the tensile wave reaches the sample from the output bar side at the same time as the torsion wave comes from the input bar. Void tests were carried out first, for preliminary analysis of the system behaviour. Then, successful tests have been conducted on samples made of AA7075 T6, both in combined and pure tension–torsion states; it has been possible to measure the tension–torsion stress–strain curves, from which the equivalent flow stress–strain curve has been evaluated and compared to the quasi-static ones.

Design the Phase Output Bar for Improving Static and Dynamic Current Distribution Among Parallel IGBTs in High Power Rectifier Bridge Arm of the Super-Conducting Tokamak (EAST)

Design the Phase Output Bar for Improving Static and Dynamic Current Distribution Among Parallel IGBTs in High Power Rectifier Bridge Arm of the Super-Conducting Tokamak (EAST)

Numerical Investigation of Tensile and Compressive Behavior of Mild Steel Subjected to High Strain Rate

Numerical simulations were conducted to validate computational and constitutive models for steel materials through dynamic material tests involving both tension and compression. These simulations involved the numerical modeling of the split Hopkinson pressure bar (SHPB) apparatus, with the appropriate loading applied directly in compression and indirectly in tension. To induce a tensile wave within the specimen, a shoulder, such as a coupler or collar, was interposed between the bars. The simulations were carried out using the LS-DYNA finite element code. In these numerical simulations of the SHPB tests, the MAT-15 Johnson–Cook material model was applied to represent mild steel. The resulting stress–strain relationships obtained under both compression and tension conditions were subsequently compared to corresponding experimental data. The primary objectives of these simulations were to determine the optimal placement of strain gauges on both the input and output bars of the tensile SHPB setup. Additionally, the simulations aimed to assess the influence of the gauge length-to-diameter ratio on the behavior of the mild steel specimen subjected to dynamic tension and compression. The results showed that the pulse produced due to the mechanical mismatch of the element at boundaries can be avoided using the length of the input bar smaller than the output bar. Further, the location of the strain gauge in the case of the output bar should be toward the output bar-shoulder interface, while in the case of the input bar, it should be considered at the center of the span of the bar.

Cyclic Impact Test with the Hopkinson Bar: Application to Granite

A laboratory scale cyclic impact loading test was developed by modifying a Hopkinson Bar test setup. The modifications involve placing a special shank piece between the striker and the rest of the setup. The shank transmits the impact loading and enables the use of compressed air for rapid reloading of the striker. The short shank is in direct contact with the specimen, i.e., there is no long input bar. With this configuration residual wave motion and reloading of the specimen is avoided. Behind the striker an output bar and momentum trap bar are placed for specimen loading measurement and removal of the wave motion in the system, respectively. The trap bar is stopped by a pneumatic actuator, which also resets the bars and the specimen before the next impact loading. The compressed air flow driving the striker is controlled by high-speed electropneumatic valves connected to a control unit and operated in simple open-loop control. Numerical simulations of both the striker motion by compressed air and dynamic loading wave propagation during impact were used in the design phase as well as setting up the test parameters. The test setup is able to produce stable cyclic impact loading at a frequency of up to 10 impacts per second with striker velocity up to 9 m/s. The feasibility of the test method is demonstrated by providing data from cyclic Brazilian disc experiments on Balmoral Red granite at both impact and quasi-static cyclic loading.

Simulation and dimensional analysis of instrumented dynamic spherical indentation of ductile metals

Finite element (FE) modeling of instrumented dynamic indentation experiments in a miniature Kolsky bar is undertaken. Geometry, including an output bar with machined spherical indenter tip, and velocity history boundary conditions are extracted directly from experimental diagnostics. The test material (i.e., substrate) is polycrystalline aluminum alloy Al 6061-T6. The constitutive model used in simulations accounts for isotropic elasticity and isotropic plasticity with strain hardening, strain-rate hardening, and thermal softening under adiabatic conditions. The FE model, with representative material parameters culled from the literature, accurately reproduces the curvature of the experimental load versus depth data for three different experimental indentation velocity histories. A framework for dimensional analysis of instrumented dynamic spherical indentation is set forth, improving upon prior work. Parametric FE simulations reveal sensitivity, or lack thereof, of the predicted response to variations in the proposed independent dimensionless variables encompassing material properties. For the indenter size, maximum depth, and maximum strain rate imposed experimentally on the order of 103/s, force-depth predictions are nearly unaffected by realistic variations in mass density, melting temperature, and thermal softening parameters when the sample is initially at room temperature. Predictions are affected by elastic constants (the elastic modulus and to a lesser extent, Poisson’s ratio), initial yield strength, two strain hardening parameters, and strain rate sensitivity. Predictions are also notably affected by initial temperature, with thermal softening prominent at high enough initial temperature or much higher loading rates. Based on the dimensional analysis, static indentation and elevated temperature indentation experiments are proposed for extraction of quasi-static and thermal material properties from previously uncharacterized metals, and dynamic indentation is proposed for extraction of rate sensitivity that cannot be obtained from static tests. Rate sensitivity obtained in this way from the novel instrumented dynamic spherical indentation experiments and FE simulations produces a parameterized stress–strain response for Al 6061-T6 reasonably validated by external studies for strain rates up to the order of 103/s.

Determination of dynamic material properties using laser measurement technique in split Hopkinson pressure bar

The split Hopkinson pressure bar (SHPB) is a commonly used technique to measure the stress-strain of materials at high strain rate. Using the strain records in the input and output bars, the average stress-strain and strain rate in the sample can be calculated by SHPB formulas based on the one-dimensional wave propagation theory. The accuracy of a SHPB test is based on this assumption. In this paper, first a laser measuring system is designed, implemented, and calibrated in order to obtain the dynamic properties of different materials using split Hopkinson pressure bar test. In this method which is a non-contact one, the displacements of bar/sample interfaces are measured directly using a laser extensometer technique, by using the provided equations, in addition to the strain, the stress of the tested sample can be calculated. Moreover, the operation of the method is evaluated using numerical simulation. Aluminum 7075 and copper C10200 samples were studied to evaluate the implemented measurement method. The comparison with other measurement methods shows good agreement of numerical and experimental results. Moreover, since the one-dimensional wave propagation is not used directly in this method, we show the proposed method can be used even with shorter pressure bars which can reduce the cost of manufacturing and maintenance of the SHPB apparatus.

Stress wave propagation through a 180° bend junction in a square cross-sectional bar

• Longitudinal stress wave can flow through a 180° bend as if it were a straight rod. • Long duration waves can be recovered without distortion after navigating the bend. • 1-D wave propagation principles successfully describe the phenomena for long waves. • Flexural waves are generated at the junction due to asymmetric deformation. • The junction behaves as a low pass filter and can be used to shape the pulse. Longitudinal elastic stress wave propagation through a 180° bend junction connecting two square bars is analyzed using analytical and numerical approaches and validated against experiments. The aim is to identify conditions under which the one-dimensional stress propagation principles can be applied to this geometry despite complete reversal of the stress wave path and study the mechanism of wave propagation through this geometry. By assuming the junction to move as a rigid body parallel to the input wave direction, the influence of the bend is analyzed for different pulse shapes and durations. For long duration stress pulses, the bend allows the stress wave to “flow” through the junction without distortion, whereas for short duration stress pulses, the wave undergoes significant dispersion. The junction behavior was further analyzed using finite element analysis and the results compared well with those of the analytical model. The wave motion through the junction results in asymmetric deformation of the junction, which generates flexural waves of different amplitudes in both the input and output bars. In general, stress pulses with constant peak amplitude and a smooth transition to the peak value suffer minimal dispersion as they traverse the junction. It is concluded that one-dimensional stress wave theory can be used to successfully model the propagation of long-duration longitudinal stress pulses around a 180° bend junction.

Dynamic photoelastic experimental study on the influence of joint surface geometrical property on wave propagation and stress disturbance

Rock joints significantly affect the dynamic response of rock masses and the stability of underground structures . In this study, the dynamic photoelastic test was conducted to investigate the influence of joints on the stress field and wave propagation . The photoelastic equipment as well as the Split Hopkinson Pressure Bar (SHPB) were adopted for the test. The specimen sandwiched between the input and output bars was composed of two polycarbonate plates. One side of the plates was uneven with a few notches, while other sides were smooth and flat. The artificial joints were simulated by the contact of the uneven and flat sides of the two plates. The relation between the stress wave propagation and the stress field around the joint was studied when the joint has different contact area ratios, joint thicknesses, and joint surface distributions. The test results show that compared to the joint thickness, the joint contact area ratio and the joint surface distribution have a significant influence on the wave propagation and stress field near the joint. The transmitted wave is highly correlative with the stress field. This work provides a beneficial attempt to reveal the stress field disturbance and the effect of joint geometrical properties on wave propagation from the photoelastic test.

SrxTi0.6Fe0.4O3−δ (x = 1.0, 0.9) catalysts for ammonia synthesis via proton-conducting solid oxide electrolysis cells (PCECs)

The high concentration of OVs and active sites of S0.9TF promote its high NRR activity. The proton-conducting solid oxide electrolysis cells (PCECs) with S0.9TF material as a cathode showed a high output (bar) and durability (line).

Simulation-Assisted Design of a Power Stack for Improving Static Current Sharing Among Three IGBT Modules Connected in Parallel

In this study, cosimulation with Q3D and Simplorer were adopted to design a single-phase power stack with equal output current on three paralleled IGBT modules in high power application, therefore, the derating of total current will be reduced, which can improve the current utilization and power density of power stack. The performance of the designed stack was verified using a double-pulse test (DPT). The circuit used in the DPT regarded the power stack output current as static current, which is a critical index to evaluate current sharing. The static current sharing among the IGBT modules was mainly dependent on the stray inductance of the DC busbar, IGBT modules, and phase output bar (POB), which is used to connect the IGBT modules to load, in parallel paths of the power stack. Cosimulation was performed to determine the stray inductance of the IGBT modules, DC busbar and POB, and a constant-current-slope method was used to verify the inductance. Subsequently, design the shapes of DC busbar and POB for attaining maximum ratio of imbalanced current (MRIC) of the three IGBT modules is within 3% under 200% (2400A) rated current. The cosimulation results indicated that the MRIC of the current paths in power stack were 0.8%. Finally, three IGBT modules and a gate driver were used to construct power stack with 1000V DC link. The experimental results obtained by DPT indicated that the MRIC was 0.9% under 200% rated current, demonstrating the effectiveness of the proposed stray inductance design method.

The Symmpact: A Direct-Impact Hopkinson Bar Setup Suitable for Investigating Dynamic Equilibrium in Low-Impedance Materials

BackgroundMeasuring the dynamic behavior of low-impedance materials such as foams is challenging. Their low acoustic impedance means that sensitive force measurement is required. The porous structure of foams also gives rise to dynamic compaction waves, which can result in unusual behavior, in particular if the foam material is so thick, that dynamic force equilibrium is not reached.ObjectiveThis work investigates comparatively large polyurethane foam specimens with densities in the range of 80 – 240 kg/m3 to deliberately achieve a state away from force equilibrium during high-rate compaction. The aim is to understand how an increase in strain rate leads to a reduction in strength for such materials.MethodsA specialized direct-impact Hopkinson bar is employed. It uses polycarbonate bars to achieve the required long pulse duration of 2.6 ms to compress the large specimens into the densification regime. In contrast to existing setups, both striker and output bar are instrumented with strain gauges to monitor force equilibrium. The absence of an input bar allows monitoring force equilibrium more accurately. Special attention is paid to the calibration of strain gauges, taking non-linear effects, wave dispersion and attenuation into account. Digital Image Correlation is employed to analyze elastic and plastic compaction waves by means of Lagrange diagrams.ResultsDepending on density, the specimens show saturation of dynamic strength increase at high rates of strain approx 500 /s, or even negative strain rate sensitivity in case of the lowest density. The occurrence of apparent negative strain rate sensitivity is accompanied by a localized structural collapse front, moving at a low velocity of approx 10 m/s through the material. This apparent strain rate sensitivity is a structural effect which is related to the thickness of the specimen.ConclusionsThe primary aim of material characterization using Hopkinson bars is to achieve a state of force equilibrium. For this reason, very thin specimens are usually employed. However, data gathered in this way is not representative for thick foam layers. Here, an increase of strain rate can lead to a decrease of strength if homogeneous deformation is replaced by a dynamic compaction wave. This behavior can occur at strain rates encountered under conditions such as automotive crash.

Effects of Acute Caffeine Intake on Power Output and Movement Velocity During a Multiple-Set Bench Press Exercise Among Mild Caffeine Users.

The main goal of this study was to evaluate the effectiveness of an acute dose of caffeine (6 mg/kg body mass (b.m.)) on power output and bar velocity during a bench press multiple-set resistance training session in participants with mild daily caffeine consumption (in the range of 1 to 3 mg/kg/b.m). Thirteen recreationally active male participants (age: 21.9 ± 1.2 years, body mass: 74.4 ± 5.3 kg, body mass index: 23.1 ± 1.6 kg/m2, bench press onerepetition maximum (1RM): 79.2 ± 14.9 kg), with daily caffeine ingestion of 1.56 ± 0.56 mg/kg/b.m., participated in the study with a randomized double-blind experimental design. Each participant performed two identical experimental sessions, 60 min after the intake of a placebo (PLAC) or 6 mg/kg/b.m. of caffeine (CAF-6). In each experimental session, participants performed 5 sets of 5 repetitions of the bench press exercise with a load equivalent to 70% 1RM. The eccentric and concentric phases of the bench press exercise were performed at maximal possible velocity in each repetition. Bar velocity was recorded with a linear position transducer and power output was calculated using velocity and load data. A two-way repeated measures ANOVA indicated no significant substance x set interaction for mean power output (MP), mean bar velocity (MV), peak power output (PP) and peak bar velocity (PV). However, there was a significant main effect of substance on MP (p < 0.01; η2 = 0.47) and MV (p < 0.01; η2 =0.45). Post hoc analysis for main effect revealed that MP and MV values in the CAF-6 group were higher than in the PLAC group in all 5 sets of the exercise (p < 0.05). In conclusion, this study demonstrated that an acute dose of caffeine before resistance exercise increased mean power output and mean bar velocity during a multiple-set bench press exercise protocol among mild caffeine users.

Strain Rate Dependence of Dynamic Flow Stress of 6061-T6 Aluminum Alloy at Strain Rates ranging from 1× 10&lt;sup&gt;3&lt;/sup&gt; to 4× 10&lt;sup&gt;4&lt;/sup&gt;s &lt;sup&gt;-1&lt;/sup&gt;

In order to evaluate the strain rate dependence of the dynamic flow stress of 6061-T6 aluminum alloy, strain rate reduction tests are conducted in the strain rate range from about 2×104 to 4×104s−1, which is the strain rate range before reduction, and the reduction in strain rate is 58.6%. To eliminate an effect of elastic wave dispersion produced in a bar on the measured flow stress, a output bar being 2mm in diameter is employed. A steep increase in the flow stress was observed at the strain rate of about 2×104s−1. A simplified model for dislocation kinetics under dynamic plastic deformation is used which can represent a transition in the rate controlling mechanism of dislocation motion from a thermally activated process to a viscous drag. It is comfirmed that the steep increase in the flow stress of 6061-T6 observed at the strain rate of about 2×104s−1 is attributed to the rate dependence of the viscous drag on the dislocation motion and furthermore, the increase in the mobile dislocation density lowers a velocity of moving dislocations and shifts the transition region, or the strain rates in which the steep increase in the flow stress becomes to appear, to the higher strain rate side.

Impact of Ischemic Intra-Conditioning on Power Output and Bar Velocity of the Upper Limbs.

This study evaluated the effects of ischemic conditioning on power output and bar velocity in the bench press exercise. Ten healthy males (age: 25 ± 2 years; body mass: 92 ± 8 kg; bench press one repetition maximum −1RM: 145 ± 13 kg), took part in two experimental sessions (with and without ischemia), 1 week apart in random and counterbalanced order. In the ischemic condition, cuffs placed around the upper part of the arms were inflated to 80% of arterial occlusion pressure before each set, while in the control condition there was no blood flow restriction. The exercise protocol included 5 sets of three repetitions each, against a resistance equal to 60% 1RM, with 5 min recovery intervals between sets. There was a main effect of condition for mean power output (MP) and mean bar velocity (MV) (p = 0.01), with overall MP being higher in ischemia than in control by 5.6 ± 4.1% (mean ± 90% compatibility limits), a standardized effect size (ES) of 0.51. Overall MV was also higher by 5.5 ± 4.0%, ES = 0.63. Peak power output (PP) and peak bar velocity (PV) were similar in set 1 of the control and ischemia condition (1039 ± 105 vs. 1054 ± 82 W; 684 ± 74 vs. 696 ± 53 W; 1.09 ± 0.07 vs. 1.12 ± 0.09 m/s; 0.81 ± 0.05 vs. 0.82 ± 0.05 m/s, p = 0.67 to 0.99, mean ± standard deviation). However, from set 3 onward (p = 0.03 to 0.001), PP and PV were higher in ischemia compared with control, with the highest difference observed in set 5 (10.9 ± 5.9%, ES = 0.73 for PP and 8.6 ± 4.6%; ES = 0.89 for PV). These results indicate that ischemia used before each set of the bench press exercise increases power output and bar velocity and this may be used as performance-enhancing stimulus during explosive resistance training.

Dynamic testing and simulation of 9 mm full metal jacket ammunition

Ballistic protection for armed forces requires a continuous performance improvement to successfully face ever evolving threats and scenarios. Ballistic tests are conventionally carried out in order to assess and validate the levels of protection to a high degree of accuracy. Although very effective, those tests are often time consuming and lack the necessary flexibility. A better approach would be to set up a numerical protocol for a number of simulations and only carry out final real life validation tests. Unquestionably, the main advantage of finite element modelling is the possibility to simultaneously evaluate a wide variety of configurations and their interactions (materials, geometry, architecture, etc.). For reliability, it is necessary to use sufficiently precise material behaviour models to accurately transcribe the phenomena observed during the impact. Our study focuses on the mechanical behaviour of 9 mm ammunition materials, namely a lead alloy core and a steel alloy jacket. For this purpose, a preliminary study (not presented here), was carried out on both the lead core and the steel jacket separately and the parameters for each constitutive model were determined. Lead-steel cylindrical samples, extracted from the ammunition, have been used for the validation of the entire constitutive model. By utilizing those samples, a high degree of the ammunitions material properties have been retained. SHPB tests have been carried out in multiple conditions, varying the striker speeds and temperatures. Additionally, the tests were recorded with an ultra-high speed camera. Strain gages were used to record signals along the input and output bars. Those measurements have been compared to numerical results using Finite Element code (ABAQUS® Explicit). A very satisfying correlation between the experimental data and the simulation has been reached, thus validating the jacket and core constitutive models and interactions for subsequent studies of ballistic impacts.

Exploratory Tests on a Biaxial Compression Hopkinson Bar Set-up

Multiaxial dynamic loadings occur in many industrial cases and multiaxial dynamic test development is thus a crucial issue. To meet this challenge, a biaxial compression Hopkinson bar set-up is designed. The set-up consists of a striker, an input bar, an internal output bar and a co-axial external output tube (surrounding the internal bar). The internal output bar measures the axial loading of the cross sample whereas the external output bar measures the transverse one via a mechanism. This mechanism uses two intermediate parts with inclined sliding surfaces. Gauges on the bars enable for force measurements in the set-up, and the sample displacement field is obtained by digital image correlation. Simple compression tests on cuboid samples inserted between the input bar and the internal output bar give the sample material behavior. Then, to determine the friction at the mechanism sliding surfaces, identical samples are inserted between the input bar and the external output bar, and are compressed. Finally, the consistency of the measurements obtained during a biaxial compression test on a cross sample can be checked from the previously measured parameters and from numerical simulations.

Mechanical characterization of textile reinforced cementitious composites under impact tensile loading using the split Hopkinson tension bar

Strain-hardening cement-based composites (SHCC) reinforced additionally with continuous textile reinforcement exhibit a high tensile strength, ductility and low crack width up to failure localization, being suitable as strengthening layers on structural elements subject to impact loading. The quasi-static tensile properties of such composites are usually derived on long, planar specimens, as dictated by the geometry of the textile reinforcement and by the necessity of sufficient yarn anchorage. However, with regard to high strain rate testing in split Hopkinson bar systems, both the length and the planar shape of the textile reinforced specimen represent major drawbacks. This explains the lack of comprehensive investigations on the mechanical performance of textile reinforced cement-based composites from the perspective of material characterization. This paper presents two new configurations of a gravity-driven split Hopkinson tension bar (SHTB) purposefully developed for investigating the tensile behavior of such composites under strain/displacement rates in the range of impact loading. The first configuration is designed for uniaxial tension tests on planar textile reinforced composites. The planer specimens are attached to the input and output bars using special aluminum adapters. The influence of the adapters and of specimen geometry on wave propagation and dynamic stress equilibrium is discussed in detail based on the results of experimental and numerical investigation. Corresponding amendments to the traditional wave analysis and suitable evaluation methods are proposed for an accurate assessment of the material response. Additionally, a novel testing configuration for single-yarn pullout experiments is presented. This setup allows for a detailed description of the rate effects on the bond between textile yarns and cementitious matrix.

Design and simulation of a compact and ultra-wideband polarization beam splitter based on sub-wavelength grating multimode interference coupler

A compact and ultra-wideband multimode interferometer (MMI)-based polarization beam splitter (PBS) is designed in a silicon-on-insulator (SOI) platform. A sub-wavelength grating (SWG) structure is employed in the multimode region to reduce the overall length of the structure and also increase its operating bandwidth. Instead of using the beat-length difference to separate the transverse electric (TE) and transverse magnetic (TM) polarized waves, the TM waves are directly coupled to the output bar port through an interconnecting waveguide, while the TE polarized waves are transmitted to the cross port by the self-imaging process. This substantially reduces the length of the PBS and the overall footprint can be as small as 4.8 × 21 µm2. The proposed device exhibits the extinction ratio of more than 15 dB in a 250 nm wavelength range (1.38–1.63 µm) and more than 12 dB in the 350 nm wavelength range (1.3–1.65 µm) for the TE and TM polarizations, respectively. In addition, the insertion loss remains below 1.2 dB for both the TE and TM polarization in a broad wavelength range from 1.38 to 1.54 µm. The proposed PBS can be fabricated by a single-step etching process on an SOI wafer. Moreover, our simulations show the robustness of the PBS performance to the fabrication errors’.

4091 Influence of Vision and Proprioception on Motor Control in ASD

OBJECTIVES/GOALS: Sensorimotor integration deficits are common in Autism Spectrum Disorders (ASD). There is evidence for both an over-reliance on visual and proprioceptive feedback during motor control in ASD, suggesting deficits in the ability to modulate sensory feedback processing in order to use the most reliable input. This study aims to test this hypothesis. METHODS/STUDY POPULATION: 40 persons with ASD (ages 10-33 yrs) and 25 age-, sex- and nonverbal IQ-matched controls completed precision gripping tasks under multiple proprioceptive and visual feedback conditions. Participants squeezed a force sensor with their index finger and thumb and tried to match their force output to a target force. Visual feedback of the target force (stationary bar) and their force output (bar that moved up/down with increased/decreased force) were displayed on a computer screen. Visual feedback was presented across low, medium, and high gain levels; the force bar moved a greater distance per change in force at higher gains. Proprioceptive feedback was manipulated using 80Hz tendon vibration at the wrist to create an illusion that the muscle is contracted. Force regularity (approximate entropy; ApEn) was examined. RESULTS/ANTICIPATED RESULTS: We have scored data from 18 participants with ASD and 13 control participants to date. Preliminary results from these participants indicate a Group x Tendon Vibration x Visual Gain interaction for ApEn (F = 1.559, p = 0.023). Individuals with ASD show slight increases in ApEn with 80Hz tendon vibration relative to no tendon vibration in all visual conditions. Controls showed increased ApEn during 80Hz compared to no tendon vibration at low visual gain but decreased ApEn with tendon vibration at high visual gain. These preliminary results indicate that controls shift to using a secondary source of sensory feedback (e.g., proprioception) when the primary source (e.g., vision) is degraded. However, persons with ASD do not reweight different sensory feedback processes as feedback inputs are degraded or magnified. DISCUSSION/SIGNIFICANCE OF IMPACT: Our preliminary results reveal that sensorimotor issues in ASD result from deficits in the reweighting of sensory feedback. Namely, persons with ASD fail to dynamically recalibrate feedback processes across visual and proprioceptive systems when feedback conditions change. Our results may aid treatment development for sensorimotor issues in ASD.

Acute Caffeine Intake Enhances Mean Power Output and Bar Velocity during the Bench Press Throw in Athletes Habituated to Caffeine.

Background: The main objective of the current investigation was to evaluate the effects of caffeine on power output and bar velocity during an explosive bench press throw in athletes habituated to caffeine. Methods: Twelve resistance trained individuals habituated to caffeine ingestion participated in a randomized double-blind experimental design. Each participant performed three identical experimental sessions 60 min after the intake of a placebo, 3, and 6 mg/kg/b.m. of caffeine. In each experimental session, the participants performed 5 sets of 2 repetitions of the bench press throw (with a load equivalent to 30% repetition maximum (RM), measured in a familiarization trial) on a Smith machine, while bar velocity and power output were registered with a rotatory encoder. Results: In comparison to the placebo, the intake of caffeine increased mean bar velocity during 5 sets of the bench press throw (1.37 ± 0.05 vs. 1.41 ± 0.05 and 1.41 ± 0.06 m/s for placebo, 3, and 6 mg/kg/b.m., respectively; p < 0.01), as well as mean power output (545 ± 117 vs. 562 ± 118 and 560 ± 107 W; p < 0.01). However, caffeine was not effective at increasing peak velocity (p = 0.09) nor peak power output (p = 0.07) during the explosive exercise. Conclusion: The acute doses of caffeine before resistance exercise may increase mean power output and mean bar velocity during the bench press throw training session in a group of habitual caffeine users. Thus, caffeine prior to ballistic exercises enhances performance during a power-specific resistance training session.