Impact Force-time Curves Research Articles

Experimental investigation on the horizontal impact response of precast RC bridge piers with grouted sleeve connections considering defects

To investigate the behaviour of precast bridge piers with grouted sleeve connections under horizontal low-velocity impact loads, twelve precast reinforced concrete (RC) bridge pier specimens and two cast-in-place reference specimens were tested to study the effect of grouting defect degree, impact velocity and fabricated method (precast vs. cast-in-place) on the impact response of RC piers. The failure modes, rebar strains, impact forces, displacement, and energy dissipation capacity of both cast-in-place and precast specimens were compared and analyzed. The results indicate that due to inertial effects induced by impact loading, the peak impact forces were three to seven times greater than the peak static loads. Transverse cracks were more likely to initiate in the grout layer for precast specimens, with diagonal cracks extending from the loading position to the pier bottom after impact. As horizontal impact velocity increased, the impact force, maximum displacement, and energy absorption ratio also significantly increased. The impact force-time curves of the pier specimens with grouting fullness ranging from 30 % to 100 % showed minimal differences compared to the cast-in-place specimen. A decrease in grouting fullness led to an increase in the maximum displacement of the pier specimens and reduced the transmission of impact waves between the reinforcement bars.

Impact responses of the steel-PU foam-concrete-tube multilayer energy absorbing panel: Numerical and analytical studies

The enhancement of structural protection can be achieved by using energy absorbing structures as sacrificial layers. In this study, a new steel-PU foam-concrete-tube multilayer energy absorbing panel (SFCTMEAP) is developed to improve the impact resistance of buildings and infrastructures, and its behaviour under impact loading is numerically and analytically studied. A Finite Element (FE) model is established using LS-DYNA to further study the behaviours of SFCTMEAP, and its results (including the failure mode, displacement–time and impact force–time curves) agree well with the test data. The SFCTMEAP presents a deformation mode of local indentation of the front energy absorbing layer, flexure of the steel-concrete-steel panel and collapse of PU foam-filled steel tubes (PUFSTs). The energy dissipations of variant components of the SFCTMEAP are obtained through the FE model and the PUFSTs is the main energy absorbing component. In addition, parametric studies are performed to obtain the influences of the impact location, initial momentum of impactor and thickness of PU foam panel on the response of SFCTMEAP. The results indicates that the specimen with larger impact eccentric distance dissipates less impact energy, and raising the initial momentum of the impactor is benefit to the energy dissipation by the PUFSTs. Moreover, an analytical model is developed to calculate the displacement history of SFCTMEAP under the impact loading. The displacement responses predicted by the analytical model are found to be in good agreement with the test results.

Experimental and Field Investigations on the Impact-Resistance Mechanical Properties of Negative Poisson’s Ratio Bolt/Cable

Abstract Dynamic impact tests of negative Poisson’s ratio (NPR) and rebar bolts under different impact wavelengths were carried out using a self-developed NPR bolt tensile impact test system. Additionally, a field anti-impact test using blasting was performed to simulate rockburst, and the field anti-impact characteristics of the NPR and conventional cable were compared and analysed. The experimental test results revealed that the peak impact force of the NPR and rebar bolts was inversely proportional to the wavelength. The NPR bolt underwent only constant resistance structural deformation, and the rod body did not break. The rebar bolt body fractured and necked. Under the same impact wavelength, the impact force and elongation of the two bolt types were proportional to the impact velocity. Compared with the greater peak impact force of the rebar bolt, the NPR bolt output structure deformation reduced the peak impact force. At the same impact velocity, as the wavelength increased, the impact force of the NPR bolt decreased rapidly, and the number of peaks also decreased. The impact force peak value of the rebar bolt was high, the impact force-time curve had multipeak characteristics, and no apparent rapid attenuation occurred. The field test results indicated that the NPR cable could produce slip deformation under the action of an explosion impact force to absorb the impact energy and that it had special mechanical properties to maintain a constant resistance. Under the same equivalent blasting impact energy, the conventional cable test section collapsed completely. The NPR cable test section was stable overall, verifying that the NPR cable had better impact-resistance mechanical properties than conventional cable. The research results provide a reliable basis for the effectiveness of NPR bolts/cables in preventing rockbursts.

Effect of structure on dynamical stab-resistance behaviors of laminates composite

The dynamic stab-resistance behaviors of laminate composites composed of TA15, TA1 titanium with various thicknesses of ultra-high-molecular-weight polyethylene, and polyester fabrics are characterized under dynamic stab testing conditions and analyzed by a new method using the average velocity of tension-compaction-plastic deformation process to calculate the ratio of energy in different damage process. The damaged area is observed by optical microscopy and SEM, and the impact force-time curve and damage degree are analyzed, and the energy of different processes during the dynamic stab test is calculated. The results show that laminates with the structure of high strength material among the low strength materials have much better performance than other specimens.

A progressive damage model of composite laminates under low-velocity impact

In this paper, a progressive damage model for studying the dynamic mechanical response and damage development of composite laminates under low-velocity impact was established. The model applied the Hashin and Hou failure criteria to predict the initiation of intra-laminar damage (fiber and matrix damage); a linear degradation scheme combined with the equivalent displacement method was adopted to simulate the damage development; a cohesive zone model with the bilinear traction-separation relationship was used to predict delamination. A user material subroutine VUMAT was coded, and the simulation analysis of carbon fiber reinforcement composite laminates subjected to 25 J impact was performed via commercial software ABAQUS. The predicted impact force-time curve, impact force-displacement curve, and damage distribution contours among the layers were in a good agreement with the experimental, which verified the proposed model. According to the simulation results, the fiber damage and matrix damage were analyzed, and the expansion of delamination was discussed.

Effect of different microstructure on dynamical stab-resistant property of TA15 alloy

The effects of different microstructure on the dynamical stab-resistant property of TA15 alloy are investigated. The specimens were tested on the stab apparatus after heat treatment at temperature of 850, 930 and 1030°C, time of 30min and air cooled. The impact force-time curves, microstructure and fracture morphology of specimens were analyzed. The results showed that the properties of higher strength and plasticity are benefit to the performance of stab resistance of TA15 specimens, and the curves of 930°C and 850°C exhibit two peaks and longer time ranges, but the curve of 1030°C exhibits the shortest time to reach the peak of impact force, and the specimens heat treated at 850°C exhibit the better performance against the knife impactor because of fine grain and stronger grain boundary binding force to absorb the impact force energy.

Research of Dynamic Constitutive Model of Reinforced Concrete Based on LS-DYNA

Bridge structure in life span, in addition to the need to withstand permanent and variable action, there may be large or small under dynamic loading, such as impact, explosion, earthquake etc. In order to get the real response of the structure under dynamic load, based on reasonable dynamic constitutive model, a nonlinear finite element analysis is needed. In this paper, several commonly used models of concrete dynamic constitutive model for ship collision with bridges are introduced: Reinforced concrete damage model (RC damage model), Elastic-Plastic Cap model, HJC model and Elastic model. Then the simulation analysis of two impact tests of rigid beads strike the target concrete walls and hammer strike the RC beams are carried out by using the analysis software LS-DYNA for nonlinear dynamic analysis. In the analysis, the influence of the various dynamic constitutive models on the impact structure is compared, and the calculated dynamic impact force-time curve and displacement-time curve are compared with the experimental data. It is found that the RC damage model can better simulate the change of concrete damage, and can simulate the development of structural cracks more realistic, and can consider the influence of reinforcement ratio on the impact force. Based on this, a multi parameter sensitivity analysis is made on the RC damage constitutive relationship, and the practical formula of the impact force is put forward. Research shows that the maximum impact force increases with the increase of the ratio of reinforcement, and the impact of the ship bridge collision analysis should be considered.

Finite element analysis of dynamic progressive failure of plastic composite laminates under low velocity impact

This paper studies dynamic mechanical responses and damage mechanisms of plastic fiber-reinforced polymer matrix composite laminate under low velocity impact. First, the plastic damage model is introduced for intralaminar damage, where Puck’s failure criteria and strain based damage evolution laws for fiber and matrix are used, and the bilinear cohesive model is adopted for delamination. Second, an uncoupled numerical scheme for dealing with the intralaminar plastic deformation and damage evolution by finite element analysis (FEA) is originally proposed based on the strain equivalence hypothesis, in which the effective stresses and strains are first solved using the backward Euler algorithm and then the nominal stresses and damage variables are updated independently. Finally, the proposed algorithm is implemented using ABAQUS-VUMAT by the time stepping algorithm. For two composite specimens under transverse impact, the impact force-time curve, the impact displacement-time curve and the dissipated energy at different impact energies are studied by comparing the results using experiments and FEA. Numerical results show the plastic damage model leads to higher precision than the elastic damage model as the impact energy becomes relatively large.

Dynamic response of expanded polystyrene concrete during low speed impact

The impact response of lightweight concrete filled with expanded polystyrene beads (EPS concrete) has been studied experimentally using a drop hammer system equipped with a high speed photography system. According to the impact force-time curves and the images of specimen surface obtained during the tests, the impact response of EPS concrete can be summarized as a four-stage procedure. The damage of EPS concrete is found to be a progressive process, which initiates from the upper part and develops downwards, leading to fluctuation of impact force. Based on the experiments, the energy dissipation capability of EPS concrete is evaluated, which demonstrates a dependence on the fracture mode of EPS concrete at the impact velocities in a range of 2–4m/s. The energy dissipation capacity of EPS concrete is found insensitive to the EPS volume fraction, when it is in a high range from 70.2 to 80.3vol%. Up to 18.6% increase in energy dissipation is observed in the concrete with 80.3vol% EPS under impact at 4m/s.

Numerical Simulation Analysis of Collision between Ship and Steel Sheet Pile Quay-Wall

The impact process of 50000t ship and steel sheet pile bulkhead is simulated by finite element software ANSYS/LS-DYNA. This article acquires the impact force-time curve, equivalent force-time curve of steel sheet pile and the pressure-time curve of breast wall. Comparing the impact force of numerical simulation with the result of ship-bridge collision specifications, and general rules and characteristics are obtained. At the same time, put forward some measures to prevent the damage of wharf structure under the ship of large velocity impact, which provide theoretical references during the design, maintenance, and transformation of similar wharf.

The use of experimentally-determined impact force as a damage measure in impact damage resistance and tolerance of composite structures

An instrumented drop-weight impact rig, ultrasonic C-scan and CAI test rig form a basic experimental system needed for the quantitative investigation of impact damage resistance and damage tolerance assessment. It is shown that it is essential to have an impact rig designed with certain traits along with other selected impact conditions so that dominant damage mechanisms occurring during impact can be identified with the threshold forces of recorded impact force-time curves. The so-determined impact force data are used to study impact damage resistance. It is demonstrated that the ratio of measured threshold impact forces is a useful alternative to residual compressive strength usually used for damage tolerance assessment. This provides a fast and cheap technique without resort to complex and expensive CAI tests.

Polyethylene toughened by CaCO 3 particles: The interface behaviour and fracture mechanism in high density polyethylene/CaCO 3 blends

Tensile behaviour and impact force-time curves of high density polyethylene/CaCO 3 blends have been investigated. The results showed that there may exist a flexible interfacial area with lower stiffness than the matrix. The concept of yielding in the interfacial area was proposed to explain the fracture mechanism of HDPE/CaCO 3 blends. Three types of fracture behaviour were assumed to be dependent on the surface-to-surface interparticle distance: (1) cavitation and crazing; (2) coexistence of cavitation and yielding in the interfacial area; (3) interfacial area yielding and matrix yielding. Based on the results, the interface conditions for brittle-ductile transition and core-shell morphology of CaCO 3 particles were discussed.

Full-scale aircraft impact test for evaluation of impact force

Previously, estimates of the force caused by aircraft impact into rigid structures have been determined using theoretical methods based on the aircraft's calculated mass and strength distribution. However, these methods required many assumptions to be made and they left many questions unanswered. Because of the uncertainty involved in these analytical predictions of impact force, a full-scale aircraft impact test was performed and an extensive set of response measurements was analyzed to evaluate the impact force against a rigid target. The analysis and evaluation gave an accurate impact force-time curve under the test condition and confirmed the practical use of an existing analytical method. An analysis with a lumped mass spring model also provided good agreement with the test results.

Analysis of the impact force by a transient liquid slug flowing out of a horizontal pipe

An abrupt increase in the gas flow rate in a horizontal gas-liquid two-phase stratified or wavy flow induces a transient slug flow. When this transient liquid slug flows out of a pipe, it applies a large impact force by its impingement on a structure located outside the pipe. The shape of this impact force-time curve is characterized by such quantities as initial impact force, maximum force, acting period of force and total momentum. The influences of each volumetric flux of two phases and of the pipe diameter on the impact force-time curves and the dynamic behavior of the transient liquid slug are experimentally studied and theoretically analyzed on the basis of Dukler-Hubbard's model by applying equations of the integral balance of mass and momentum to the transient liquid slug. The calculated results agree well with the experimental results of the dynamic behavior of the transient liquid slug and of the impact force.

The Behaviour of the Impact Damper

In this investigation a theory is developed relating to the behaviour of the impact damper. The analysis is based on the assumptions that (1) two un-equispaced impacts per cycle occur in the steady state, and (2) the impact force-time curve is of rectangular shape and of infinitesimal duration. Fourier series are used to represent the impact cycle and the differential equation of motion is derived. This is solved using the dynamic equations of impact to determine the boundary conditions. Three equations are developed to determine the variation of impulse, phase angle and vibrational amplitude with the change of the damper parameters. Resonance curves are obtained and the theory is examined experimentally. The regions of validity of the above assumptions are studied both theoretically and experimentally. Non-linearity in the behaviour of this damper is very clear, especially in the range of its optimum behaviour. Two design curves are developed which can be used to determine the damper parameters necessary for a certain amplitude reduction.

Photoelastic study of elastic impact on the edge of a plate

The Hertz impact theory assumes a quasi-static stress distribution adjacent to the point of contact. This assumption has been tested by a plane photoelastic investigation. The impacting bodies were made from glass plate, which is well suited to impact tests because at high rates of loading it is purely elastic up to fracture and shows no relaxation. Its small photoelastic sensitivity is an advantage for the investigation of high local stresses. A disadvantage is its large elastic modulus giving high propagation velocities. An apparatus based on single-shot exposure has been developed allowing us to follow quasi-cinematographically the wave propagation in the impacted plate at time intervals of micro-seconds with an exposure time determined by a spark of 0·6 μsec half-value duration. The fringes at the point of impact could be photographed very sharply with this arrangement because of their low velocities. The isoclinics were also photographed at various instants during the impact time which was between 45 and 100 μsec according to the impacting mass. Comparison of photographs with others taken under static compression of the same bodies in similar conditions confirms the similarity of the stress distribution near the impact or contact point. Hence the impact force can be determined photoelastically by static calibration. The maximum impact forces found in this way for the various impact masses and velocities coincide well with those calculated from the elementary theory. As an additional check, the area of the surface of contact was measured under static and dynamic loading. A comparison with the values calculated from the Hertz theory would be inaccurate because the impact duration was of the same order of magnitude as the natural period of the impinging bodies and hence smaller than the impact duration according to Hertz. The quasi-cinematographical series of photographs shows clearly the vibrations excited in the impacting bodies. The coefficient of restitution, which relates mainly to this part, could be determined from the impact force—time curve and the impulse. The fracture strength of glass proved appreciably higher under impact than under static loading.