Impulsive Loading Research Articles

Discovering causal models for structural, construction and defense-related engineering phenomena

Causality, the science of cause and effect, has made it possible to create a new family of models. Such models are often referred to as causal models. Unlike those of mathematical, numerical, empirical, or machine learning (ML) nature, causal models hope to tie the cause(s) to the effect(s) pertaining to a phenomenon (i.e., data generating process) through causal principles. This paper presents one of the first works at creating causal models in the area of structural and construction engineering. To this end, this paper starts with a brief review of the principles of causality and then adopts four causal discovery algorithms, namely, PC (Peter-Clark), FCI (fast causal inference), GES (greedy equivalence search), and GRaSP (greedy relaxation of the sparsest permutation), have been used to examine four phenomena, including predicting the load-bearing capacity of axially loaded members, fire resistance of structural members, shear strength of beams, and resistance of walls against impulsive (blast) loading. Findings from this study reveal the possibility and merit of discovering complete and partial causal models. Finally, this study also proposes two simple metrics that can help assess the performance of causal discovery algorithms.

A Framework for Structural Analysis of Icebreakers during Ramming of First-Year Ice Ridges

This paper presents a framework for structural analysis of icebreakers during ramming of first-year ice ridges. The framework links the ice-ridge load and the structural analysis based on the physical characteristics of ship–ice-ridge interactions. A ship–ice-ridge interaction study was conducted to demonstrate the feasibility of the proposed framework. A PC-2 icebreaker was chosen for the ship–ice interaction study, and the geometrical and physical properties of the ice ridge were determined based on empirical data. The ice ridge was modeled by solid elements equipped with the continuous surface cap model (CSCM). To validate the approach, the simulated ice resistance was computed using the Lindqvist solution and in situ tests of R/V Xuelong 2. First, the local ice-induced pressure on the hull shell was determined based on numerical simulations. Subsequently, the local ice pressure was applied to local deformable sub-structural models of the PC-2 icebreaker hull by means of triangular impulse loads. Finally, the structural response of sub-structural models with refined meshes was computed. This case study demonstrates that the proposed framework is suitable for structural analysis of ice-induced stresses in local hull components. The results show that the ice load and the structural response obtained based on the four first-year ice-ridge models show obvious differences. Furthermore, the ice load and corresponding structural response increases with the width of the ridge and with increasing ship speed.

Development of a prediction model of dynamic deflections for asphalt pavements under FWD impulse loading

Pavement deflections are critical indicators in pavement design and acceptance programs. Falling weight deflectometer (FWD) technique has been widely adopted to measure the dynamic deflections in pavement engineering. Although the dynamic effect of FWD impulse loading on deflections is significant, FWD deflections are still commonly interpreted and examined using the static analysis programs in acceptance projects because of their ease of implementation and high computational efficiency. This may lead to an inability to effectively control the construction quality of pavements. Accordingly, this study aims to propose a simple and accurate approach for converting static deflection to dynamic deflection. Layered elastic theory (LET) and spectral element method (SEM) were adopted to generate the theoretical static and dynamic deflection databases, respectively. Based on the databases, a simple approach is proposed to predict the dynamic deflection only using four static deflections. The proposed approach shows lower computational workload and higher accuracy than other traditional formula forms which include equivalent layer moduli and thicknesses. In the field engineering cases, the calculated static deflections can be 2 ∼ 3 times higher than the measured ones, while the predicted dynamic deflections from the proposed approach match the theoretical dynamic deflections well and are comparable to the measured deflections for both asphalt pavements with asphalt binder or inorganic binder bases and granular bases. This indicates that dynamic deflections can more effectively control the construction quality of asphalt pavements in the FWD deflection-based design program. Meanwhile, the drawbacks of traditional prediction methods are investigated and evaluated. The proposed approach exhibits simpler form and higher accuracy, while avoiding the drawbacks of traditional methods. Combining with the common static LET-based programs, the proposed approach provides a more reasonable and practical way for the construction quality acceptance of asphalt pavements using FWD data.

Numerical Simulation and Influence of Non-Gaussian Vibrations on Flexible Robotic Systems

Random vibration excitation is a standard method for obtaining the dynamic properties of aerospace structures and simulating loading conditions. Shaker-based random excitation and traditional finite element analysis techniques use random vibrations, assuming a Gaussian distribution of excitation impulse magnitudes. While Gaussian signals may sufficiently describe some vibrational environments, many real-world excitations have non-Gaussian distributions. These signals may contain vibrational impulses larger than those observed in a Gaussian signal and could cause damage if not considered. This paper examines the influence of non-Gaussian signals on flexible vs. rigid robotic architectures using NASA JPL’s Pop-Up Flat Folding Explorer Robot (PUFFER) and Cooperative Autonomous Distributed Robotic Explorer (CADRE). The results indicate that flexible systems can be significantly impacted by a non-Gaussian excitation profile and that neither a typical enveloping of a Gaussian excitation nor a superposition of the responses to a worst-case impulse load with the response to a Gaussian signal was sufficient to bound the response due to non-Gaussian excitation. The driving mechanism for increased sensitivity of flexible robotic systems appears to be inertial, and designers may consider shifting the relative flexibility of the system or its constraints to force particular deformation modes or designing hinge mechanisms with increased damping to minimize the influence of non-Gaussian signals on the response of a flexible robotic structure.

Study of vibration shock processes of non-linear mechanical systems with distributed parameters

In practice, under the conditions of perfection and constructive development of modern equipment and machines, nonlinear mechanical systems with distributed parameters are often encountered, which, depending on the principles of operation, are affected by vibration shock. Therefore, the study of vibration shock processes of the mentioned systems has great theoretical and practical importance and as a result to determine the optimal parameters of vibration protection devices to ensure their safe operation. In our case, the displacement field of two interacting non-linear mechanical systems with distributed parameters is considered, when their interaction is of vibration shock nature. Obviously, the mentioned events are more pronounced when the self-oscillation frequency of one or both systems momentarily approaches the frequency of forced vibration shock processes. In addition, critical moments are fixed during the phase shifts of forced oscillations of oscillatory systems, in this case, the frequencies of forced oscillations approach mutually opposing phase moments. By choosing the optimal parameters of hysteresis losses, it is possible to almost exclude sub-harmonic modes superimposed on the main resonance modes in vibration shock processes. During hysteresis losses of the parabolic type, the value of µ changes automatically in connection with impulsive loads, which will allow us to transfer the vibration shock processes to automatic modes and, accordingly, the practically safe operation of the mentioned systems.

Numerical study on dynamic cracking characteristic and mechanism of quasi-brittle materials under impulsive loading

This study focuses on investigating the dynamic cracking behaviors of quasi-brittle materials under impulsive loading using the extended non-ordinary state-based peridynamic (NOSB-PD) model. This extended model incorporates two stress-based failure criteria: Mohr-Coulomb and maximum tensile stress criteria, to represent shear and tensile fractures of quasi-brittle materials, respectively. By analyzing the evolution characteristics of the maximum principal stress obtained from the NOSB-PD model, the fracture mechanisms of quasi-brittle materials subjected to impulsive loading are explored. The research reveals that tensile failure predominantly governs the initiation and propagation processes of quasi-brittle materials under impulsive loading. The stress concentration effect, transfer effect, and dissipation effect observed in the maximum principal stress fields provide insights into the cracking mechanism during the failure processes of such materials. To validate the findings, the crack initiation modes and crack propagation paths obtained from the NOSB-PD model are compared with those obtained from the existing experimental and numerical approaches. The results demonstrate that the extended NOSB-PD model is effective in addressing fracture problems associated with quasi-brittle materials under impulsive loading conditions.

Stability analysis of power quality under complex operating conditions

This article draws inspiration from the derivation of the failure model of ordinary components under impulse loads and obtains a calculation method for the forced outage rate of power equipment under impulse loads. Based on the revised forced outage rate, the reliability of the power system under impulse loads is evaluated. By comparing and analyzing the reliability of the power grid under two scenarios: impulse loads and conventional loads, the impact of impulse loads on the operational risk of the power grid is obtained.

Exploring the possibility of undesirable manufacturing heritage reduction in parts made of composites and their joints

The object of the research is the possibility of improving the quality of parts made of composites (CM) by means of pre-polymerization treatment of the wet package with intensive pulse loading. The existing technologies for forming parts from CM involve the compaction of the collected impregnated package of reinforcement layers and their subsequent polymerization under the influence of pressure and temperature. As a result of this technology, residual thermal and shrinkage stresses occur in the composite package, which lead to undesirable spatial deformations of profile parts, a violation of monolithicity in the areas of the connection of the composite and metal ends. Using the example of an angular composite profile with a profile with doubler on one of the caps, the residual stress calculation is given and the method of choosing rational angles for stacking the reinforcing material is demonstrated in order to reduce the amount of residual thermal stresses that arise in the composite during its polymerization. The dependence of the twisting parameter of a long-dimensional composite profile of constant cross-section along its axis on the modulus of elasticity and the coefficient of linear temperature expansion is plotted. The work explains the mechanism of the emergence of such harmful technological heredity. The value of the residual deformations was estimated. Based on the analysis of the impregnation process of dry reinforcing material with a binder, the task of increasing the maximum contact area of the binder with fibers is formulated and a possible method of its increase is analyzed. Thus, using the model of capillaries between the fibers of the composite, it is concluded that it is necessary to apply additional pressure to the binder for its deeper advancement between the fibers. Using a synergistic method of combining knowledge from various branches of industry and based on experimental data, a process of pre-polymerization loading of the impregnated package with intense impulse loading (shock waves) is proposed. This process greatly improves the quality of parts of the units produced.

State-of-the-Art Polyurea Coatings: Synthesis Aspects, Structure-Properties Relationship, and Nanocomposites for Ballistic Protection Applications.

This review presents polyurea (PU) synthesis, the structure-properties relationship, and characterization aspects for ballistic protection applications. The synthesis of polyurea entails step-growth polymerization through the reaction of an isocyanate monomer/prepolymer and a polyamine, each component possessing a functionality of at least two. A wide range of excellent properties such as durability and high resistance against atmospheric, chemical, and biological factors has made this polymer an outstanding option for ballistic applications. Polyureas are an extraordinary case because they contain both rigid segments, which are due to the diisocyanates used and the hydrogen points formed, and a flexible zone, which is due to the chemical structure of the polyamines. These characteristics motivate their application in ballistic protection systems. Polyurea-based coatings have also demonstrated their abilities as candidates for impulsive loading applications, affording a better response of the nanocomposite-coated metal sheet at the action of a shock wave or at the impact of a projectile, by suffering lower deformations than neat metallic plates.

Damageability of Metals under Impulse Loading

Impulse loading of a sample of limited dimensions (at least two free surfaces) leads to the oscillation of the sample in the standing wave mode as a consequence of wave reflection from the faces and their interaction with each other. Localized strain bands originate and evolve at the standing wave nodes (wave interference zone), where the deformation of the material occurs in the compression-tension mode and the stress in the wave interference zone does not exceed the spall strength of the material. (Excessive stress leads to the formation of spall cracks and sample destruction). As a result of the absence of energy transfer through the nodal points,which is typical of standing waves, the deformation of the sample can last for a long time after passing a shock wave until dissipative processes would bring about oscillatory process damping. Another characteristic feature of standing waves is the formation of new harmonics with their own wavelengths and vibration eigen frequencies with new spall damage occurring at each node.

Hetero‐blast from a structural reactive material cylinder under explosive loading

AbstractA structural reactive material (SRM) cylinder is considered here as a limiting case of a dense metallic energetic system in which a mixture of metal particles is consolidated to the theoretical maximum density excluding porosity, to possess both high energy density and mechanical strength. Dynamic fragmentation and free‐field explosion of a 103 mm inner diameter SRM cylinder charge is experimentally studied, with a wall thickness varying in a range of metal‐to‐explosive mass ratio M/C=1.3 to 4.0. Under explosive loading, the SRM cylinder produces a designated fragment size distribution divided into two groups: fine fragments with sizes on the order of 102 μm and below, and coarse fragments with sizes on the order ranging between 100‐101 mm. Prompt detonation shock‐induced reaction (DSIR) of the expanding cloud of high‐concentration fine fragments supplements the energy to enhance the primary blast as it propagates, while the coarse fragments form a high‐speed, high‐concentration metal momentum flux crossing the fireball and blast front to contribute to the total impulse loading to a nearby structure. Rapid impact‐induced reaction (IIR) of the secondary fragments from high‐speed coarse SRM fragments further enhances the reflected blast loading or generates a high interior explosion pressure as fragments perforate into the structure. The above distinctive characteristics of a unique hetero‐blast are coupled effectively in the near‐field range.

Experimental and theoretical study on the response of the X-frame CFRP sandwich beam under the local impulsive loading

The impact resistance of the carbon fibre reinforced X-frame sandwich beam and its foam reinforced structure was investigated experimentally and theoretically. To simulate the blast loading on the composite sandwich beams, the aluminum foam projectiles were utilised to impact the composite specimens. Under the local impulsive loads of the different intensities, the core shear failure, core crushing and skin fracture of the sandwich beams were observed by using a high-speed camera. A theoretical model for the dynamic response of the fibre-reinforced composite sandwich beam under the impact loads was constructed. Three phases, namely the local compression, the propagation of global bending/shearing wave and global stretching were considered in this theory. The theoretical model can provide the reasonable deflection history and failure modes of the sandwich beam compared with the experimental and simulated results. The impact pressure between the foam projectile and the beam were obtained by the theoretical and numerical predictions. The results indicated that the decreasing of the structural density can reduce the transmitted impulse. The optimal design charts were constructed by introducing the normalised variables based on the theoretical model. The minimum weight design revealed that the composite sandwich beams with low-density cores generally had the better specific impact resistance, while the foam-filled sandwich beams with the higher density had the outperformed impact resistance at the low impulse. It is expected that the theoretical model can provide a useful reference for predicting the impact resistance of the fibre-reinforced composite sandwich structures.

A Virtual Mechanical System control law for energy transfer towards a single actuation point in [formula omitted] DOF buildings

Mitigating vibrations in engineering structures is of key interest, as they can lead to failure and/or discomfort. However, in some cases it is not feasible to actuate all the structure’s degrees of freedom, which makes vibration mitigation difficult. In this work, we investigate the addition of a single one-degree-of-freedom virtual mechanical system (VMS), as an active controller, to attract and mitigate the energy from an impulse load on the structure. To challenge the controller, an actuation point is chosen furthest away from the impact location. As it is implemented virtually, the coupling between the structure and VMS can be chosen freely. It is found that a skew-symmetric coupling generates a gyroscopic force that enables control over the structure’s mode shapes. Using this, the controller is tuned to achieve a beating phenomenon that attracts the vibration energy to the actuation location. A nonlinear damper, based on the slope of the envelope of the virtual velocity state, avoids reflection of energy to the structure and dissipates this unwanted energy. Furthermore, the virtual damper’s robustness to timing errors is investigated: damping too soon means an incomplete energy transfer to the VMS, damping too late leads to return of energy to the building. The tuning strategy of the VMS is applied to a 4 DOF and 60 DOF building benchmark. For comparison, a tuned mass damper (TMD) and a nonlinear energy sink (NES) are tuned as well. The VMS succeeds in decreasing the settling time significantly in both cases, while the performance of the passive TMD and NES is rather limited for this specific configuration.

The Shielding Effect of the Built in Damper Cage in a Synchronous Machine.

Because of the cost efficiency of modern machines, the design of a damper winding in a synchronous machine must be met the following both subjects. One criterion is a functional design, and a second one is an as cheap as possible design. Normally, the complete damper cage is substituted by the slot wedges of the rotor. But this replacement cage isn’t as effective as the original cage [1]. Furthermore the damping moments of the eddy currents in the massive rotor and in massive parts of a synchronous machine don’t changed. So in the case of an absent damper winding the sum of the damping moments decreases. In order to answer the question of the aims of a built in complete damper cage it must be differentiated between synchronous generators and motors. Generators have to produce sinusoidal voltages. As a result, the damping of higher harmonics in the generator is important. Furthermore, the damping of the negative sequence caused by an increased asymmetric load must be defined by the consumer. Normally, a five percent asymmetric load is acceptable. In the case of synchronous motors the damping of load impulses are important. One result is the difference between the damping moment of a complete built in damper cage and an incomplete built in damper cage. In addition this paper treats about the damping of higher harmonics and the damping of the negative sequence rotating field.

Numerical Study of the Vibrations of Beams with Variable Stiffness under Impulsive or Harmonic Loading

Numerical Study of the Vibrations of Beams with Variable Stiffness under Impulsive or Harmonic Loading

FURTHER DEVELOPMENT OF GDEM FOR THE MODELING OF MULTI-SCALE DYNAMIC RESPONSE OF ROCK SUBJECTED TO BLASTING AND IMPACT

The dynamical responses of rock subjected to blasting and impact have been of concern in most underground projects. Due to the size effects and strain-rate enhancement induced by inertial effects, the dynamic responses of rock and underground structures show multi-scale characteristics. Thus, in order to achieve better understanding of multi-scale dynamic responses of rocks, both computation accuracy and numerical efficiency have been taken into account. This is achieved by further development of a continuum-discontinuous element method code, called GDEM, with a new type of dynamic bounding-surface damage model being implemented, thus forming a bounding-surface dynamic plasticity damage-GDEM model (DB-GDEM). A dynamic bounding-surface damage model is adopted, with the strength surface of Holmquist-Johnson-Cook model being employed as bounding surface. The concept of critical state, strainrate hardening, and continuum damage evolution has been taken into account for both brittle and ductile responses of rock. The model performance has been demonstrated by a few numerical simulations, including the Landau blast model, explosions under various confinements, and trapezoidal impulse loading, etc. By comparing modeling results among DB-GDEM model, linear-elastic model in GDEM, and D-P model in GDEM, it is noted that the contribution of plasticity-damage can result in the decay of stress waves and deterioration of dynamic strength. Both continuous and discontinuous mechanical behaviors of rocks have been captured well by the newly developed DB-GDEM model. The main multi-scale dynamic characteristics of rock subjected to blasting and impact, including particle movement, fragmentation of rock mass, stress-wave propagation, and failure models, have been captured. The introduction of bounding-surface plasticity damage model in GDEM would reproduce a more realistic dynamic damage response of rock compared with the original GDEM model that embedded with conventional constitutive models.

Deformation behavior of super-austenitic stainless steel sandwich panels subjected to air blast and underwater explosion

Super-austenitic stainless steel is a class of high alloy steels with enhanced toughness, outstanding strength, and corrosion resistance. In this article, the structural integrity of super-austenitic stainless steel square sandwich panels subjected to surface and underwater explosions is investigated through numerical simulations, and the results are validated with experiments. Abaqus Explicit Solver is used to predict the face deformation and core crushing failure modes of the sandwich panels. Simulations are performed for three levels of impulse load by varying the explosive quantity. The fluid-structure interaction is established by CONWEP and UNDEX algorithms for air blasts and underwater explosions respectively. The dynamic deformation behavior of the sandwich panel is modeled using the Johnson-Cook (JC) plasticity model incorporating strain rate and temperature effects. Good agreement is witnessed between the numerical predictions and experimental observations. An increment in deformation of the face sheet, cell wall buckling, and core compaction is observed with the increase in the impulse. From a series of air and underwater explosion simulations, the advantage of using sandwich structures for blast mitigation is demonstrated. In addition, the significance of numerical simulations to limit experiments and predict the deformation of the sandwich panels is presented.

Vibration Energy Harvesting from Plates by Means of Piezoelectric Dynamic Vibration Absorbers

In this paper, the possibility of harvesting energy from the vibrations of a plate is analyzed. The harvester takes the form of a cantilever dynamic vibration absorber equipped with a piezoelectric layer and tuned by means of a tip mass to the first mode of vibration of the plate. A mathematical model of the coupled system composed of the plate and the harvester is presented. The validity of the proposed harvester is proved by means of simulations carried out with the modal expansions approach. Simulation results highlighting the effects of harvester tuning and location are presented as well. Then, the validity of the harvester is confirmed by experimental tests carried out both with a concentrated impulsive load and with a distributed pressure load. Simulations and experimental tests are performed on the cantilever piezoelectric dynamic vibration absorber and on the same piezoelectric layer directly bonded to the plate surface. Results show an improvement in terms of generated voltage when the proposed novel device is used in place of the simple layer.

Effect of porosity on rapid dynamic compaction of nickel nanopowder.

The shock-loading behavior of nanomaterials requires careful investigation because these complex systems are widely used in environments subjected to impulsive loads. Planar plate impact experiments are conducted to study shock compaction waves in 94% porous nickel powder containing spherical ∼55 nm particles in the pressure and strain rate ranges of 0.1-0.4 GPa and 106-107 s-1, respectively. The distinct two-step structure of these waves is captured by a laser velocimetry technique with high time resolution. This structure is caused by the formation of faster precursor waves traveling ahead of main compaction waves. The complexity of the shock Hugoniot curve of the tested nanomaterial is described using the obtained two-wave data and earlier results for higher pressures. The effect of initial porosity on the fronts of both waves and compressed states behind them is demonstrated using the current data and those that were collected previously for 50% porous samples of similar nanopowder.

Energy absorption and storage of nanofluidic solid–liquid composite material under high strain rates

Efficient energy absorption and dissipation are crucial for the development of novel protective materials under intensive dynamic loadings. Nanofluidic solid–liquid composite materials (NLCs) provide a promising pathway to engineer such materials owing to their rapid and reversible energy absorption and storage performance. In this study, we conducted systematic experiments on nanoporous SiO2 based NLCs to gain a better understanding of the dynamic mechanical behavior and the underlying energy absorption and storage mechanisms under compressions with varying strain rates. Our findings indicate that the energy absorption in terms of dissipation and storage under the repeat compressive loadings includes two stages. The initial stage indicates the maximum energy absorption capacity, which is efficiently improved by the adding electrolyte solution and the retreatment. The stable energy absorbing stage represents the reversible energy absorption and storage capacity of the NLCs. Based on the noticeable strain rate effect, a three-stage mechanism is proposed to explain the significant increase of energy absorption capacity with the varying compressive strain rates. The superior reusable energy absorption capacity of NLCs holds great promise for their use as excellent energy-absorbing materials under intensive impulsive loadings.