Force Time Histories Research Articles

Crushing behavior and deformation mechanism of randomly honeycomb cylindrical shell structure

Abstract Honeycomb structure, which presents potential ability in energy absorption and impact resistance, has advantages of simplicity, lightweight, easy manufacturing and designability. In this study, honeycomb structure panel is expanded to cylindrical shell by adopting the rolled-up algorithm and the crushing behaviors of the randomly honeycomb cylindrical shell (RHCS) structures are investigated under axial loading. The influence of geometrical and topological parameters, i.e. the thickness-to-diameter ratio, cell irregularity, relative density on the deformation evolution and energy absorption performance is systematically performed. It is found that the deformation modes of RHCS structures are significantly affected by thickness-to-diameter ratio and cell irregularity. Moreover, the rate-independent, rigid–plastic hardening (R–PH) idealisation with two parameters is adopted to characterize the crushing responses of RHCS structures and the parameters are quantified as power-law relations with respect to relative density. Further, the crushing behaviors of density-graded RHCS structures with continuously varying in density are carried out under different impact velocities. Results indicated that the introduction of density gradients can strongly affect the deformation mode, crushing force and energy absorption performance of density-graded RHCS structures. Combining with analysis of crushing front propagation, the theoretical determination of crushing responses of the density-graded RHCS under different loading rates is presented based on R–PH model. The results of predicted crushing force-time histories of density-graded RHCS structures show versatile agreement with that of finite element values at both impact and support ends. Additionally, the energy absorption capacity that is related to deformation mechanisms of density-graded RHCS structures is investigated.

Deflection Calculation Based on SDOF Method for Axially Loaded Concrete-Filled Steel Tubular Members Subjected to Lateral Impact

Axial force has a great influence on the dynamic behavior and the impact resistance of concrete-filled steel tubular (CFST) members. Based on numerical simulation and theoretical analysis, the impact response and deflection calculation method for axially loaded CFST members subjected to lateral impact are investigated in this paper. The nonlinear numerical model of an axially loaded CFST member considering the strain rate effects has been established, and the simulation accuracy has been validated by comparing with existing test results. The contrastive investigation is carried out to illustrate the influence of axial load on the variation pattern of impact force for CFST members under various structural and impact parameters, and its result indicates that the impact force-time histories for CFST members with different axial loads are mainly characterized by rectangular pulse and triangular pulse. Moreover, a simplified calculation method considering the effect of axial force is proposed based on the equivalent single degree of freedom (SDOF) method, devoted to predicting the deflection of axially loaded CFST members subjected to lateral impact. The comparisons with the numerical simulation prove that the deflection calculation method has a reasonable accuracy; thus, the proposed method can be utilized in the damage assessment and anti-impact design for CFST members subjected to lateral impact and axial load.

Effect of tapered and semi-tapered geometry on the offshore piles driving performance

Pile driving procedure and efficiency is not only affected by soil parameters, but also by pile geometry including the pile shape and taper angle. Several important effective factors in pile driving are hammer blow counts, penetration and velocity developed in the pile during driving. In this paper, the drivability of different pile geometries was investigated by performing field tests and numerical analyses based on finite difference method. Four steel piles have driven by hammer blows and pile driving analyser (PDA) was used to record the pile dynamic responses. The time histories of the pile head force, settlement, and velocity have been continuously monitored under each hammer blow during the driving tests. The numerical analysis with simulating the soil-pile system in the driving process has been also investigated and compared with the obtained results from the field tests. Parametric studies have been performed on effective parameters on driving such as pile geometry and embedded length. The results indicate that the pile geometry such as tapered and semi-tapered can offer better drivability performance with decreasing cumulative hammer blow counts, increasing the piles' velocity and settlement and the efficiency of the driving operation. These are remarkable in pile driving scenario.

Measurement and Analysis of Biomechanical Outcomes of Chiropractic Adjustment Performance in Chiropractic Education and Practice

ObjectiveThe purpose of this study was to compare biomechanical measures of chiropractic adjustment performance of the McTimoney toggle-torque-recoil (MTTR) technique among students and chiropractors. MethodsFifty-three participants (15 year-3 [Y3] and 16 year-5 chiropractic students and 22 McTimoney chiropractors [DCs]) participated in this study. Each applied 10 MTTR thrusts to a dynamic load cell, 5 each with their left and right hands. Biomechanical variables including preload force, peak force, time to peak force, thrust duration, and total thrust time were computed from each of the force-time histories and compared within groups using a series of 2-way analysis of variance to evaluate the effects of sex and handedness, and between groups to determine the effect of experience using a series of 3-way analysis of variance. The Games-Howell post hoc test was used to further assess pairwise comparisons. ResultsMean time to peak force was more than 3 × shorter for DCs (69.96 ms) compared with Y3 students (230.36 ms) (P = .030). Likewise, mean thrust duration was also found to be nearly 2.5-fold significantly shorter for DCs (117.77 ms) compared with Y3 students (283.84 ms) (P = .030). The DCs took significantly less total thrust time (mean = 1.27 seconds) in administering MTTR thrusts than Y3 students (1.89 seconds) (P = .006). No significant differences were found among any of the 3 clinician groups for peak force or in time to peak force or thrust duration for comparisons of all 10 MTTR thrusts among year-5 students and DCs. Higher peak forces were observed for thrusts delivered with clinicians’ dominant hands (P = .001), and the fastest thrusts were found for the dominant hands of DCs (P = .001). Sex had no significant effect on biomechanical variables. The Y3 students had significant greater variability in thrust times for each hand and for analyses of both hands combined (P = .001). ConclusionTraining and experience were found to result in shorter MTTR thrust times and other biomechanical variables that have been identified as important factors in the mechanisms of chiropractic adjustments. Identification of such biomechanical markers as performance outcomes may be of assistance in providing feedback for training in chiropractic education and technique application.

Characterization of Spall in Hard Rock from Observations and Simulations of the Source Physics Experiment Phase I

ABSTRACTSpall signals from the Source Physics Experiments are presented, analyzed, and modeled for insight to the explosion source. The observed signal is similar in nature to nearby historical nuclear explosions, and the surface force-time history or velocity can be interpreted with the same model. We use the models for peak spall velocity, spalled mass, and spall depth and radius derived from historical nuclear explosions to parameterize the physical force-time history model from Stump (1985) and show that this parameterized model can be used for spall prediction. The spall signal is also investigated with a numerical continuum model that incorporates gravity. Peak velocity and dwell time are well predicted, and the multiple slap-down phases are captured if one includes a weak near-surface layer similar to the geologic observation.

Delamination in GLARE laminates under low velocity impact

Present paper deals with the finite element (FE) analysis for determination of impact induced delamination in GLARE laminates. Despite the fact that GLARE possesses better impact properties compared to those for both aluminium and glass/epoxy composites, the low interface strengths may lead to failure in the form of delamination and debonding under low velocity impacts (LVIs). In the present work, LVI responses of GLARE 5 and GLARE 4-3/2 are studied to compare the contact force-time history, plate deflection and delamination at the interfaces using a transient dynamic FE code developed incorporating Newmark-β method and Hertzian contact law. Results show that under LVI, GLARE 4-3/2 is more susceptible to delamination at the interfaces compared to GLARE 5-2/1. The effects of outer aluminium layer thickness and laminate configuration on the interfacial delamination in GLARE under LVI are also studied.

Experimental study on the dynamic behavior of T-shaped steel reinforced concrete columns under impact loading

This paper reports an experimental investigation into the behavior of axially loaded steel reinforced concrete (SRC) columns subjected to impact loads. A total of seven SRC columns with T-shaped steel skeleton were prepared and tested using a drop hammer impact system. The testing variables include the impact height, stirrup spacing and the axial compression ratio. The impact force time histories and lateral displacements at mid-span and quarter-span were recorded and analyzed. The experimental results indicated that the decrease of stirrup spacing resulted in a smaller lateral deflection. Axial load was also found to have a strong influence on the residual deflection of columns subjected to impact loading. In addition, the finite element analysis models, which considers the effects of strain rate of steel and concrete as well as the axial loads, were established to simulate the experiment. The FEA results are proved to agree well with that of experiment. The findings obtained from this study can facilitate the application of SRC columns in improving the impact-resistant performance of bridge and building columns.

Experimental investigation of slender RC columns under horizontal static and impact loads

This paper reports an experimental investigation on the behaviour of slender reinforced concrete (RC) columns under horizontal static or impact loading. Fourteen square RC columns were tested under horizontal impact loading by using a modern horizontal impact facility. These specimens were subjected to the same design impact velocity of 0.8 m/s. The effects of three main parameters, namely the specimen slenderness ratio, the longitudinal reinforcement ratio, and the axial compression ratio, were considered. Based on the impact test results, the descriptions of failure mode, crack pattern, time histories of impact force, deflection, and strain are illustrated. On the other hand, tests on three additional RC columns with different cross-section dimensions subjected to horizontal static loading were undertaken for comparison purpose. In the comparisons of the load–displacement relationships for static and impact load cases, the significant divergence can be observed owing to the existence of the inertial force initiated in the dynamic responses. After the completion of the impact test, six impact-damaged specimens were tested under static loading to evaluate their residual resistance and the corresponding behaviour. It is found that the ultimate capacities of damaged specimens could reduce by 7%–14% compared with those of undamaged ones.

Comparative Investigation for the Performance of Steel and Carbon Fiber Composite Front Bumper Crush-Can (FBCC) Structures in Quarter-Point Impact Crash Tests

As Light weighting is the top priority for the automotive industry today, the push for reducing overall vehicle weight will likely include the consideration of materials that have not previously been part of mainstream vehicle design and manufacturing, including carbon fiber composites. Therefore, the deformation characteristics and crush performance of carbon fiber reinforced polymer (CFRP) and steel front bumper crush-can (FBCC) assemblies in Quarter-point Impact Tests are investigated in this article. The experimental tests in this study were conducted using a sled-on-sled testing method. Force-time histories, kinematic data and videos for each test were recorded using several high-speed cameras (HSCs), accelerometers and a load cell wall. The collected data was filtered with SAEJ211 CFC 180 filter and sorted to ease the comparative analysis for the performance of the steel and CFRP bumper assemblies. A similar pattern was observed in the crashworthiness characteristics (i.e. force-time history, force-displacement, crash pulse and deformation patterns) of all steel and CFRP FBCC specimens. Typical failure modes of composite bumper assemblies, which were revealed by the high-speed videos were the failure of crush-can and failure of the bumper beam due to the generation of high stresses as it gets stretched due to its curvature after hitting the sled. On the contrary, local permanent deformation of the beam and crush-can was the predominant failure mode in steel FBCCs assemblies under quarter-point loading. Results obtained from the comparative investigation show that CFRP is a more efficient yet lighter material in regard to the absorption of the impact energy.

A comparative study on the fatigue life of the vehicle body spot welds using different numerical techniques: Inertia relief and Modal dynamic analyses

Among different parts of a vehicle, the body is the main load-bearing component and as a result, its durability is critical. Fatigue analyses are typically divided into different categories, the quasi-static methods and the dynamic methods. The aim of this paper was to compare the inertia relief and modal dynamic approaches for their formulation, accuracy and computation time. The chosen case study is the fatigue life of the vehicle body. By utilizing multi-body dynamics model and driving the vehicle on different standardized roads and by different velocities, the force and moment time histories which act on the body were calculated and later used by the finite element model for the stress analysis. Then, by using the structural stress method, the fatigue life of the vehicle spot welds were calculated and the results were compared for both quasi-static and dynamic approaches. The findings reveal that the modal dynamic method is almost 37 times more time-consuming than the inertia relief approach, but if accuracy is desired, it can be up to 96% more accurate. Also as predicted, at low frequency loading (less than 10% of the first nonzero frequency of the structure), there is no difference between the results of both methods.

Characterization of adhesive joints under high-speed normal impact: Part II – Numerical studies

This two-part article presents an experimental method with numerical verification of the characterization of adhesive bonds under normal impact loading. Part I presented the experimentally measured performance of static and impact behavior of two adhesives (a methacrylate and an epoxy). Part II presents the numerical modeling of the static and dynamic tests performed in Part I. The finite element simulations are used to determine approximate dynamic material modeling parameters. The simulations are also useful in estimating certain critical performance aspects of the adhesive for the proposed impact test such as the estimation of contact force time histories, the dynamic stress time history profiles within the adhesive, and to the various energy components in the adhesives and adherends.

Measurement and Numerical Simulation of Ground and Subgrade Vibrations of Beijing Urban Rail Line 13

Urban rail transit is an effective way to deal with the problem of traffic congestion in major cities. Trains travel through dense residential and commercial areas, providing convenient transportation while also result in vibration problems in the surrounding environment. Long‐lasting vibrations result in disturbance to people’s sleep, malfunction of sensitive equipment, and even damage to heritage buildings. Compared with elevated and tunnel sections, ground surface urban railway generates vibrations and propagates to the surroundings via a more direct path in the form of surface waves, which makes the environmental problem more prominent. Due to the complexity of the train‐track‐ground system, the characteristics of the vibration propagation and attenuation are yet to be revealed. In this paper, we investigate the vibration of the ground and the subgrade next to the Beijing Urban Rail Line 13 by a field measurement combined with a mathematical model. The duration of ground vibration is divided into two parts: the train passing time and the Doppler effect‐related tailing part. Through a regression analysis of the duration, the train passing time is identified and the train traveling speed is estimated. The attenuation relationship of ground vibration intensity is expressed by a piecewise function. In the subgrade, the vibration intensity of particle decays with increasing depth and the stress decay rate is faster than that of the acceleration. The dynamic wheel/rail interaction behaves stationary and periodic, and the magnitude fluctuates up and down with the quasi‐static axle weight. The intensity attenuation relationship fitted in this paper provides a basis for designing new lines and renewing old lines and can be used as a reference for the development of vibration‐reduction technology. The simulated time history of the wheel‐rail force provides an excitation sample for further model experiments and numerical simulation. The proposed train speed identification method may be useful for parameter identification of moving sources such as ships, automobiles, and airplanes.

Regularized Cubic B-Spline Collocation Method With Modified L-Curve Criterion for Impact Force Identification

The time history of the impact force, especially for the peak force, is vital to monitor the performance of mechanical products over the life-time. However, considering the limitation of sensing technology and inaccessibility of installing, it is always difficult or even impossible to measure the force directly in engineering practice. Therefore, a regularized cubic B-spline collocation (RCBSC) method combined with the modified L-curve criterion (RCBSC-ML) is presented to identify the impact force by easily measurable dynamic response. Because the profile of cubic B-spline is close to that of impact force, a linear combination of cubic B-spline functions is used to approximate the unknown impact force. Then the force identification equation is reformed, wherein the unknown variable changes from impact force vector to weight coefficient vector. Furthermore, the modified L-curve criterion is developed to select the optimal number of collocation points which is the regularization parameter of RCBSC method. Rich simulation studies on a five degree-of-freedoms structure and experimental studies on a simplified artillery test-bed are performed to validate the performance of RCBSC-ML method. The results illustrate that RCBSC-ML method can be used to accurately identify the unknown impact force, and compared with modified generalized cross validation criterion, the presented modified L-curve criterion is more suitable to determine the optimal regularization parameter of RCBSC method. Furthermore, compared with classical Tikhonov regularization method, RCBSC-ML method is more efficient and accurate in impact force identification.

Determination of the mechanical properties of concrete using the split Hopkinson pressure bar method

Fine-grained concrete was subjected to tests with and without a pulse shaping techniques. Procedure of dispersion shift of pulses in the measuring bars was used in processing the experimental data. The time histories of forces acting on the sample from the side of measuring bars and the strength characteristics of the material obtained on their basis are compared when using a pulse shaper and correcting the shape of pulses taking into account dispersion as well as with traditional testing and data processing.

Probabilistic Multiple Pedestrian Walking Force Model including Pedestrian Inter‐ and Intrasubject Variabilities

A probabilistic walking load model that accounts for inter‐ and intrasubject variabilities has been developed to generate synthetic vertical load waveforms induced by pedestrians. The mathematical model is based on a comprehensive database of continuously recorded pedestrian walking forces on an instrumented treadmill, having a wide range of walking frequencies. The proposed model is able to replicate temporal and spectral features of real walking forces, which is a significant advantage over conventional Fourier series models. The load model results in more realistic force time histories than previous models, since it incorporates significant components of the spectra that are omitted in Fourier series approaches. The proposed mathematical model can be implemented in vibration serviceability assessment of civil engineering structures, such as building floors and footbridges, to estimate more realistically dynamic structural responses due to people walking.

Low Velocity Impact Response of Laminate Rectangular Plates Made of Carbon Fiber Reinforced Plastics

The paper aims to present an experimental study on low velocity impact behavior of composite materials reinforced with carbon fibers. The objectives of investigations are to assess the main characteristics of impact response such as the energy absorbed by the laminate plate, the contact force as well as the indentation corresponding to different initial kinetic energies of the projectile. The experimental tests were conducted on rectangular plate specimens with dimensions of 150x100x2.5mm3, cut off from a symmetric laminate made of 8 unidirectional carbon/epoxy vinyl ester laminate that are stacked in a lay-up configuration of [0/-45/45/90]s. The energy that induced the specimen’s complete perforation as well as the energy corresponding to the level of BVID were determined with regard to typical testing conditions, such as the time varying acceleration, displacement as well as the absorbed impact energy. Moreover, for comparison purposes, the analytically results obtained for the case of an elastic impact with a projectile velocity of 1m/s, by making use of a complete model based on Kirchhoff plate theory, is presented. Within the range of elastic impact, the analytical results demonstrated their good agreement with the experimental testing data in terms of the absorbed impact energy, displacements and contact force time histories.

Study on generation mechanism of vertical force peak values on T-girder attacked by tsunami bore

The generation mechanism and characteristics of peak values of tsunami bore vertical force are investigated comprehensively and thoroughly. A scaled down two-dimensional T-girder model, whose surface is divided into a series of panels, is tested in the cases with fixed initial downstream water depth, different incoming wave height and different initial clearance. Time history of vertical force is divided into four stages, in which the impinging stage is further divided into four sub-stages. Then the contribution rates of panels to the vertical force are discussed. Results show each peak value of vertical force in the impinging stage is composed of at least one peak value of vertical force on bottom panels of the girder, the continue increase of vertical force peak value is the result of more and more panels suffering static pressure of entrapped air when the chambers are successively closed by tsunami bore. The vertical force peak values on top panels of the chambers are mainly generated by the static pressure peak values of entrapped air. The entrapped air decreases the vertical velocity of tsunami bore under already closed chambers, resulting the simultaneous occurrences of pressure peaks of entrapped air in previous closed chambers.

Dynamic processes of 2018 Sedongpu landslide in Namcha Barwa–Gyala Peri massif revealed by broadband seismic records

At 22:48 pm, October 16, 2018, a large glacial mudslide occurred upstream of the Sedongpu gully on the southern mountainside of Gyala Peri in Mainling County, Tibet. To investigate its dynamical features, the force-time history of it was inverted using the broadband recording of six stations in the Namcha Barwa network. Preliminary results of the landslide force-time history indicated that the mass of the Sedongpu landslide is about one million tonne. The velocity and displacement curves from integration implied that the mass center of the Sedongpu event slipped down for a distance of 5100 m with an average velocity of 10 m/s (peaked at about 25 m/s). The fitted displacement curve (using the motion equation) revealed that the movement of the Sedongpu landslide experienced four processes. In the first 150 s, the stability at the upper part of Sedongpu glacier broke down, and the detached glacial deposits gradually moved downward. The subsequent 70 s is the stage of acceleration for the debris flow with the velocity increased and the acceleration peaked. After encountering the leading edge of the glacial deposits, the debris flow decelerated for about 80 s as the slope of the path declined and the canyon narrowed. In the final 180 s, the debris flow might have been blocked by the leading edge of the deposit or a large topographical bend; hence, it stopped eventually. The entire process lasted for 480 s. We proposed that the surface wave generated by an earlier earthquake (about 10 min before the landslide event) in Nagqu, Tibet, played a decisive role in triggering the severe event on the basis of the prolonged impact from rainfall and regional fault activity.

Dynamic force identification based on composite trigonometric wavelet shape function

The shape function-based methods are promising in dynamic force identification. However, the selection of shape function is still an issue as it determines the identification accuracy and efficiency to a large extent. This paper proposes a dynamic force identification approach by using the composite trigonometric wavelet as shape function which takes advantage of its 'wave' property in dynamic force expression. The whole domain of the dynamic force time history is segmented into different time units following the thought of finite element discretization and the local force is approximated by linear shape functions. Subsequently the force-response equation is established by assembling the calculated responses induced by shape function forces and the corresponding measured responses of all time units. Then trigonometric wavelet shape function is added to enhance the approximation capability of shape function and improve the identification accuracy progressively. Examples are employed to illustrate the effectiveness and superiority of the proposed method.

Parametric studies on the impact response of offshore triceratops in ultra-deep waters

This paper addresses the parametric studies on the impact response of offshore triceratops subjected to low-velocity impact. Triceratops is the object of the present impact study which is one of the new generation offshore complaint platforms with three buoyant legs connected to deck by ball joints. The innovative geometric form and compliant characteristics distinguish triceratops from conventional offshore platforms. The buoyant legs in triceratops are usually designed as orthogonally stiffened cylindrical shell structures. Numerical studies are carried out using Ansys Explicit analysis solver to predict the impact response and local damage of buoyant leg of triceratops. From the impact force time history obtained through explicit analysis, the hydrodynamic time response analysis is carried out in Ansys Aqwa to predict the response of deck and buoyant legs. Parametric studies are mainly focussed on the effect on the location of the indenter, size of the indenter, type of indenter, number of stiffeners and strain-rate definition. Force displacement curves are reported along with detailed numerical observations.