Peak Impact Force Research Articles

Effects of extreme cyclic loading on the cushioning performance of human heel pads under engineering test condition.

Human heel pads commonly undergo cyclic loading during daily activities. Low cyclic loadings such as daily human walking tend to have less effect on the mechanical properties of heel pads. However, the impact of cyclic loading on cushion performance, a vital biomechanical property of heel pads, under engineering test condition remains unexplored. Herein, dynamic mechanical measurements and finite element (FE) simulations were employed to explore this phenomenon. It was found that the wavy collagen fibers in the heel pad will be straightened under cycle compression loading, which resulted in increased stiffness of the heel pad. The stiffness of the heel pads demonstrated an inclination to escalate over a span of 50,000 loading cycles, consequently resulting in a corresponding increase in peak impact force over the same loading cycles. Sustained cyclic loading has the potential to result in the fracturing of the straightened collagen fibers, this collagen breakage may diminish the stiffness of the heel pad, leading to a reduction in peak impact force. This work enhances understanding of the biomechanical functions of human heel pad and may provide potential inspirations for the innovative development of healthcare devices for foot complex.

Experimental and Numerical Study on the Low Velocity Impact Behavior of ABR Pipe

The low velocity impact load on pipes during transportation, construction and operation will cause pipeline damage and lay hidden dangers for the safety of pipeline engineering. To study the low velocity impact performance of pipes made of acrylate polymer blended with polyvinyl chloride resin for water supply (ABR), 20 sets of specimens with different heights and different masses of drop hammer were carried out to study the mechanical properties of ABR pipes. Based on the impact time curve, the energy dissipation capacity and impact peak value of ABR pipe specimens were analyzed, and the empirical calculation formula of impact force peak based on the test data is obtained by the dimensional analysis method, with a relative error ranging from −7.8% to 4.1%. Moreover, the finite element numerical simulation of ABR pipe specimens subjected to impact load is carried out, and the strain development law and failure mode of the pipe under low-speed impact load are analyzed. Therefore, the calculation formula of peak impact force and failure mode proposed in this paper can provide safety assessment methods for pipeline engineering designers and constructors.

Impact-aware task-space quadratic-programming control

Robots usually establish contacts at rigid surfaces with near-zero relative velocities. Otherwise, impact-induced energy propagates in the robot’s linkage and may cause irreversible damage to the hardware. Moreover, abrupt changes in task-space contact velocity and peak impact forces also result in abrupt changes in robot joint velocities and torques; which can compromise controllers’ stability, especially for those based on smooth models. In reality, several tasks would require establishing contact with moderately high velocity. We propose to enhance task-space multi-objective controllers formulated as a quadratic program to be resilient to frictional impacts in three dimensions. We devise new constraints and reformulate the usual ones to be robust to the abrupt joint state changes mentioned earlier. The impact event becomes a controlled process once the optimal control search space is aware of: (1) the hardware-affordable impact bounds and (2) analytically computed feasible set (polyhedra) that constrain post-impact critical states. Prior to and nearby the targeted contact spot, we assume, at each control cycle, that the impact will occur at the next iteration. This somewhat one-step preview makes our controller robust to impact time and location. To assess our approach, we experimented its resilience to moderate impacts with the Panda manipulator and achieved swift grabbing tasks with the HRP-4 humanoid robot.

High strain rate effects in masonry structures under waterborne debris impacts

Masonry buildings are vulnerable to extreme hydrodynamic events such as floods or tsunamis. Post-disaster surveys have shown that waterborne debris impacts can significantly damage masonry walls during these events. To simulate these actions, the current design or research practice is to compute the force–time diagram of the impact and then use it for dynamic analyses. Standing on the current knowledge, debris impacts are highly impulsive, but it is not clear if such loads are fast enough to activate the high strain rate effects in masonry, i.e. the strain rate dependency of material properties. The present study aims to answer this question, for the first time, following nonlinear Finite Element (FE) simulations. Simulations are conducted on a masonry wall, following a micro-modelling strategy, subjected to water flow and waterborne debris impact under different scenarios. It is found that the strain rates exceed the critical threshold after which strain rate effects are considerable. Such a finding, initially obtained using the minimum design demand for log-type debris imposed by ASCE/SEI 7-22, is further extended to a range of impact force–time diagrams different in impact duration and peak force (corresponding to different debris properties or flow velocity). It is also shown that the impact location (i.e. midspan or close to the boundary) affects the strain rate magnitude because of the changes in the impact stiffness and the activated failure mechanisms. Furthermore, it is found that the dynamic tensile post-elastic behaviour of the materials is the most influencing parameter in the structural response. These results open a new area in the field of assessment and design of masonry structures to waterborne debris and guide the development of future experiments, numerical simulations or design relations.

Impact behaviour of tunnel lining assembled from non-planar interlocking steel fibre reinforced concrete bricks

In this study, a new design of tunnel lining assembled from non-planar interlocking segments was developed and tested. The new tunnel segment is made of steel fibre reinforced concrete (SFRC), and it has six symmetrical side surfaces with a concave-convex topology, which can prevent the movement of each element in the interlocked tunnel. A series of lab-scale drop weight tests were conducted to investigate the performance of the interlocking SFRC tunnel specimen under impact. A special aluminium mould was designed to cast the developed tunnel segments, and a novel testing frame was developed to allow the drop hammer to hit on the inner surface of the tunnel specimen. The peak impact force, the displacement of the drop hammer and the failure pattern of the interlocking SFRC brick were measured and analysed, considering the influences of hammer dropping height and confining load on the dynamic behaviour of the interlocking SFRC tunnel specimen.

Performance of thin reinforced concrete slabs against low velocity repeated impact load

The use of thin reinforced concrete slabs for buildings has more advantages than beam supported slabs, slabs with column capitals, and drop-down panels because of its easier construction and economic feasibility. However, it is susceptible to localized failure due to punching shear resulting in progressive collapse of the structure. Therefore, the attempt has been made to study the behaviour of thin reinforced concrete slabs 1200 × 1200 mm having thicknesses of 50 and 30 mm under repeated loading through the experiment and simulations. The mass of the impactor was 60 kg with 35 and 70° angular motion and the corresponding impact velocity were 2.62 and 4.97 m/s, respectively. Based on the member response under static conditions using analytical methods, the flexural failure was found to be more prominent and the ultimate flexural load for 50 mm thick slab was found to be 101.7% higher as compared to 30 mm thick slab. It was concluded that the resistance of the target was found to increase by 36% when the target thickness increased from 30 to 50 mm at 35° pendulum impact whereas the same was found to be 63% increment at 70° pendulum impact, during the first impact. Under repeated impacts, the impulse on both 30 and 50 mm thick slab was found to decrease gradually against 35° pendulum impact whereas the abrupt decrease in impulse was observed at 70° impact. The numerical analysis was performed using ABAQUS/EXPLICIT to predict the response of the slab under multi-impact loading. The numerical model was able to accurately predict the peak impact force on both 30- and 50-mm thick slab, up to the fourth impact.

Experimental and numerical studies on hydrodynamic effects of ice floe drift and impact process in uniform current

The safety of offshore structures is often threatened by the impact load of isolated ice floes. However, the accurate estimation of the impact load can be challenging due to the unquantified near-field hydrodynamic interaction. In this paper, the hydrodynamic interactions between ice floes and offshore structures are investigated by a model experiment and the numerical calculation. The model experiment is conducted to study the whole process of a model ice drifting and impacting a cylinder under the influence of uniform flow. Meanwhile, the interaction process is also numerically simulated by using the Computational Fluid Dynamics (CFD)-Finite Element Method (FEM) coupling method. The experimental and numerical results show good agreement in terms of velocity time histories, peak impact forces and peak accelerations. The influences of current velocity, ice floe size, and ice floe shape on various interactions are discussed based on numerical results, including the velocity attenuation effect before impact, the added mass effect during collision, the kinetic energy and motion attitude of the ice floe. The main findings of present research suggest that the viscous effect in near-field and the bow wave are noteworthy factors causing the velocity attenuation of the ice floe and ignoring these influences can lead to underestimation of the velocity attenuation effect to some extent. Additionally, the (effective) added mass coefficients calculated based on the ice floe motion equation and the momentum balance equation are found to be close to each other. However, with the decreasing of the ice floe size, the difference between the added mass coefficients calculated by the two methods gradually increases.

Understanding the impact response of bird strikes on engine blades using a novel wedge-Hopkinson bar system

Bird strikes on engine blades, as a major concern for aviation safety, are complex impact events in which structural responses and bird deformations are coupled. To investigate the slicing process during a bird strike, a wedge-Hopkinson bar (WHB) system was developed to simulate a bird striking an engine blade. The system simplifies the measurement of impact responses by using strain gauges mounted on the bar to detect the signals. Systematic tests were conducted to determine the variation of impact responses using real birds with different masses and velocities. The peak impact force, transferred momentum, equivalent impact force, and time corresponding to the momentum centroid were obtained from the force-time histories to describe the impact process. The results identify the constancy of the normalized peak impact force and the normalized equivalent impact force against the impact velocity. However, the ratio of momentum transfer was found to decrease with increasing velocity. The experimental results for strikes on a wedge and strikes on an oblique planar plate revealed a reduction in the momentum transfer for the slicing state, leading to an impact of lower severity.

A novel analytical framework for assessing the impact response of SFRC beam

This paper presents a novel model for predicting the impact response of steel fiber reinforced concrete (SFRC) beams. The model utilizes the principles of energy conservation and impulse-momentum theorem to calculate the maximum reaction force and peak impact force. A tensile behavior model for simulating the concrete behavior is proposed considering the effect of volume fraction of steel fibers and the effect of strain rate on the concrete properties. Additionally, the conventional beam theory, along with a cross-section-layered approach, is used to express the total beam's reaction forces vs deflection relationship. Afterwards, the model calculates the maximum midspan deflection of SFRC beams subjected to impact loading by applying the principle of conservation of energy and considering the effect of strain rate. The proposed model is compared with 121 impact tests, and the results show that the model can estimate the maximum reaction force of SFRC beams with acceptable accuracy.

Lateral impact resistance of CFST cantilever members stiffened with encased I-shaped CFRP

The lateral impact resistance of cantilever concrete-filled steel tubular (CFST) members stiffened with encased I-shaped carbon fiber reinforced plastic (CFRP) profiles subjected to lateral impact is investigated in this paper. The impact tests are performed on four specimens to examine the dynamic response. Finite element analysis models are established and verified against tested results. Baseline simulations are also created using the validated models to further analyze the damage pattern and energy dissipation mechanism of each component in the impact events. It is found that compared with traditional CFST members, the new composite members have higher peak impact force, lower dynamic displacement, and larger energy dissipation capacity. Additionally, the effects of design parameters on the impact performance are evaluated by parametric analyses, and the results provide valuable suggestions for developing design guidance.

Multiple response optimization of wood sawdust/natural rubber foam composites for stair tread covers

Examination of the optimal condition for wood sawdust (WS)/natural rubber (NR) foam composites is important for developing force-absorbing materials that can reduce the likelihood of accidents and injuries to the elderly. In this study, the Box–Behnken design and response surface methodology were used in experiments to determine the optimal condition for foam composites. The effects of the blowing agent, wood sawdust, and forming temperature on mechanical characteristics were also investigated. It was found that energy absorbed by the foam composites decreased with an increase in WS contents, but the hardness increased as well. The peak impact force of the foam composites reduced with the increasing addition of the blowing agent, though the coefficient of friction rose. Further, the fitted models were employed for optimization based on a desirability score that balanced multiple responses. An optimal condition for the WS/NR foam composites used to produce stair tread covers consisted of a blowing agent of 12 phr, wood sawdust of 44 phr, and forming temperature of 117 °C. Foam composites made with this condition had effective mechanical properties that closely agreed with the predicted values from the fitted models.

Lateral impact test and inertial force of concrete-filled steel tube column

The mechanical behavior of concrete-filled steel tube (CFST) subjected to lateral impact was studied by drop hammer test and finite element method (FEM). Lateral deformation occurred when the midspan of CFST was impacted by a drop weight. Two plastic hinges were formed in the mid-span and near the fixed support, respectively. The numerical and experimental results were compared to ensure that the numerical model was reasonable for investigating the stress development, damage, and inertial force of the CFST column. The effects of the impact velocity, impact mass, cross-sectional steel ratio, and boundary conditions on the inertial force of the CFST column were analyzed. During the impact process, the maximum stress was at the steel tube part of the impact location and the fixed support, while the other parts were still in the elastic or elastoplastic stages. The region under restraint at the fixed end of the CFST column exhibited the first signs of concrete core damage under tension, followed by the region near the location of the impact at midspan. At the peak impact force (Fp), the impact velocity had a considerable influence on the distribution of inertial force of CFST, while the impact mass and cross-sectional steel ratio had no discernible impact on the inertial force at the Fp, and boundary conditions had little impact on the distribution of inertial force. Based on a research of the inertial force at the Fp, a simple mechanical model of the inertial force was built.

Experimental and numerical analysis of low-velocity impact damage of CFRP laminates with negative Poisson ratio (NPR) rubber protective layer

Carbon fiber-reinforced polymer (CFRP) structures are widely used in aviation industry, which can sustain damage during assembly from low-velocity impact events, decreasing residual stress and bearing capacity. A method of negative Poisson ratio rubber protective layer placing on the CFRP structures has been proposed to address this. The influence of cell angle on the impact response and protection effect were first investigated in this study. The experimental results indicate that the negative Poisson ratio rubber protective layer enhanced the impact resistance of the CFRP laminates, which reduces 33.1% the impact peak force and 17.5% the absorbed energy. Moreover, the impact resistance of CFRP with increases with the increasement of the cell angle. A low-velocity impact finite element model was developed with mixed-mode damage criterion for laminates and the hyperelastic model for rubber. The simulation results were validated with the experiment results in impact response and delamination damage. Additionally, the impact response and resistance were analyzed by varying seven different structural parameters of the protective layer to reveal the influence of relative volume. The experiment and simulation results demonstrated that the impact resistance increased with increasing cell angle and relative volume of the negative Poisson ratio rubber protective layer.

A simplified analytical method for lateral dynamic responses of a transmission tower due to rockfall impact

Transmission tower structures support high-voltage power lines that carry electricity over long distance and rockfall is one of critical disasters during its safe operation. This paper presented a simplified analytical methodology for lateral dynamic responses of a transmission tower structure due to rockfall impact. At first, the lateral dynamic displacement of a lattice transmission tower structure can be represented by a second-order partial differential equation and half sine wave was used for rockfall impact. Then, the solution can be approximated by a set of specified shape functions multiplied by time-dependent generalized coordinates. And the partial differential equation is discretized into a set of single degree of freedom system. And then the shape function can be determined by solved an eigenvalue function and the fundamental frequency of a transmission tower can was derived based on the energy method and combination synthesis method. Finally, the lateral dynamic displacements can be approximately obtained. A numerical study of a transmission tower was conducted. Parametric study of the effect of impact location height, impact duration, peak impact force, as well as the distribution of cross-arms on dynamic responses were also carried out. And the results show that the discrepancy between the analytical and the computed of fundamental frequency is less than 3%, the error of dynamic displacement is within 10%, and the fundamental frequency of the structure decreases with the increase of the tower top additional mass ratio.

Investigation on the Impact Response of Concrete Beams Reinforced with Hybrid Steel–BFRP Bars

An appropriate hybrid form of steel and fiber-reinforced polymer (FRP) bars in reinforced concrete members can prevent steel corrosion and ensure capacity and ductility. To investigate the impact resistance of concrete beams reinforced with hybrid steel and basalt FRP (BFRP) bars, a three-dimensional numerical model was developed that takes into account the strain-rate strengthening effect. The validity of the numerical model was first verified. Subsequently, drop hammer impacts were simulated on 10 concrete beams reinforced with hybrid steel–BFRP bars to determine the influence of the BFRP bar proportion and position on their impact resistance. The results indicated that the level of concrete damage in the hybrid bar–RC beams is between those of the concrete beams with steel bars and concrete beams with BFRP bars. As the proportion of BFRP bars increased from 0 to 1, the peak impact force and internal force of the beams linearly decreased by 20%, the reaction force linearly declined by 50%, while the peak midspan displacement linearly increased by 20%. Except for the midspan deflection, the comparable degree of damage among beams with four different bar configurations indicates the equivalent impact resistance of the beams. The change in the frequency of the hybrid bar–RC beams before and after impact loading can reflect their impact resistance.

Research on the multiple successive impact resistant behaviors of biomimetic laminated basalt fiber-reinforced composite with double-twisted Bouligand structure

Basalt fiber-reinforced composite (BFRC) is extensively used in various fields such as rail transportation and aerospace. However, how to design the structure of BFRC to optimize its impact resistance remains a great challenge. Herein, inspired by the double-twisted Bouligand structure of coelacanth scales, a biomimetic BFRC is prepared. Significantly, the peak impact force of double-twisted BFRC (DT-BFRC) is 3408.12 N, which increases by 48.56% compared with unidirectionally laminated BFRC (UL-BFRC). The maximum residual elastic modulus of DT-BFRC reaches 7.88 J, which is 236.75% higher than that of UL-BFRC. This work offers a promising way to efficiently develop impact resistant BFRC.

Low-velocity impact of square conical gradient aluminium foam-filled automobile energy-absorbing boxes

In this paper, the low-velocity impact and lightweight design of the square conical gradient aluminium foam-filled automobile energy-absorbing boxes (EABes) is numerically studied. Firstly, the validity of the finite element calculation model is verified by comparing with the experimental results. Then, the influences of the conical bottom angle, tube-wall thickness, the number, position, height and depth of induction grooves, and the parameters of gradient foam on the energy absorption properties of the EABes under axial low-velocity impact are studied. After that, the mitigation and energy absorption of square conical gradient aluminium foam-filled automobile EAB are optimised. The results indicate that the aluminium tube-wall thickness has no obvious effect on improving the energy absorption properties of the EAB, and other factors have good effects on improving the energy absorption properties of the EAB. Compared with the constant cross-section EAB before optimisation, the peak impact force (F max) of the finally optimised square conical gradient aluminium foam-filled automobile EAB reduces by 22.4%, and the specific energy absorption (SEA) increases by 59.8%. The investigation is helpful for the design of the square conical gradient aluminium foam-filled automobile EAB.

Validation of In-Shoe Force Sensors during Loaded Walking in Military Personnel.

The loadsol® wireless in-shoe force sensors can be useful for in-field measurements. However, its accuracy is unknown in the military context, whereby soldiers have to carry heavy loads and walk in military boots. The purpose of this study was to establish the validity of the loadsol® sensors in military personnel during loaded walking on flat, inclined and declined surfaces. Full-time Singapore Armed Forces (SAF) personnel (n = 8) walked on an instrumented treadmill on flat, 10° inclined, and 10° declined gradients while carrying heavy loads (25 kg and 35 kg). Normal ground reaction forces (GRF), perpendicular to the contact surface, were simultaneously measured using both the loadsol® sensors inserted in the military boots and the Bertec instrumented treadmill as the gold standard. A total of eight variables of interest were compared between loadsol® and treadmill, including four kinetic (impact peak force, active peak force, impulse, loading rate) and four spatiotemporal (stance time, stride time, cadence, step length) variables. Validity was assessed using Bland-Altman plots and 95% Limits of Agreement (LoA). Bias was calculated as the mean difference between the values obtained from loadsol® and the instrumented treadmill. Results showed similar force-time profiles between loadsol® sensors and the instrumented treadmill. The bias of most variables was generally low, with a narrow range of LoA. The high accuracy and good agreement with standard laboratory equipment suggest that the loadsol® system is a valid tool for measuring normal GRF during walking in military boots under heavy load carriage.

Influence of fibre orientation, moisture absorption and repairing performance on the low-velocity impact response of woven flax/Elium® thermoplastic bio-composites

The importance of natural reinforced bio-composite materials with desirable properties such as high modulus-to-weight ratio, good impact resistance, and the ability to be easily repaired is crucial in the industry. A woven flax/Elium® thermoplastic bio-composite is manufactured to challenge these needs. Elium® is the only resin that permits the manufacture of large parts with thermoset-like processes, as Liquid Resin Infusion presented in that work. The paper highlights the influence of stacking fibre orientation, moisture absorption, and repair aptitude on its impact resistance. An instrumented drop tower was needed to conduct low-velocity impact tests at several energies and high-speed image coupled with microscopic observations was used to assess the damage evolution. The impact resistance was improved for the dry (0/90)6 orientation, but moisture absorption decreased its impact peak force by 20%. A three-point bending test was preferred to compression after impact for studying the residual properties after impact. The bio-composites with (±45)6 orientation showed higher impact residual performance than the (0/90)6 orientation, and corresponded to the reduction of maximum bending force by 20% than that of the reference. In addition, a thermo-compression process was applied to repair the impacted plates and conduct multiple impact/repair cycles which showed a significant recovery of stiffness and maximum impact force at 4J on (0/90)6 plates, highlighting their potential for repair in the automotive and marine industries.

Experimental and numerical investigation on the lateral impact responses of CFST members after exposure to fire

The impact load acting on structure can cause a completely different structural response from the static load, and structure may be subjected to both impact and fire in extreme events, leading to severe structural damage or collapse. This paper reports the lateral impact responses of concrete-filled steel tubular (CFST) members after fire. Nine CFST specimens with different parameters, i.e., the fire duration time, impact heights, and boundary conditions, were tested using an electric furnace and a drop hammer impact system. The failure modes, impact force, midspan deflection, and energy absorption were investigated and compared. Results reveal that post-fire CFST members exhibit global bending failure under lateral impact, and increasing the fire duration time reduces the impact resistance of CFST members, with lower peak and plateau impact forces but larger deflection. The finite element (FE) model of post-fire CFST members under lateral impact was developed and calibrated against the test results to further analyze the impact responses. In addition, simplified methods were proposed for the evaluation of dynamic flexural capacity, plateau impact force and maximum deflection of CFST members subjected to lateral impact.