Impact Bar Research Articles

The Fate of Bars in Braided Rivers

Ancient river deposits are important archives of past landscape conditions on planetary surfaces. On Earth, they host valuable groundwater, energy resources, and carbon-storage potential. Reconstructing details of paleochannel forms and movements refines our understanding of the controls on river behavior under different climate, landcover, and tectonic conditions, and improves predictions and models of subsurface reservoirs. While studies have shown detailed connections between channel kinematics and bar-deposit architecture in meandering river systems, similar connections between braided river movements and preserved braided river deposits have not been established. Here we explore the potential for connecting braided river deposits to paleochannel movements, form, and flow conditions, and we evaluate the controls on bar preservation using synthetic stratigraphy generated with a numerical morphodynamic model. We investigate how attributes of channel morphodynamics, like channel widening or braiding intensity, impact bar deposits’ preservation, scale, geometry, and architecture. We then assess how the scale, preservation, and facies composition of bar deposits reflect formative flow conditions of the channel. Our results demonstrate that no diagnostic signature of braided channel morphodynamics is recorded in bar-deposit geometry, facies, or preservation patterns. Rather, the unique local history of thread movements combines stochastically to preserve or rework bar deposits, and the timing of channel avulsion is the dominant control on bar preservation. Our results also show that representative paleochannel flow conditions will likely be accurately reflected in aggregate observations of braid bar deposits within channel-belt sandbodies at a regional or member/formation scale. These results demonstrate the need for broad sampling and statistical approaches to subsurface prediction and paleo-flow reconstruction in ancient, braided river deposits.

Study on Dynamic Mechanics of Node-Enhanced Graded Lattice Structure and Application Optimization in Automobile Energy Absorbing Box.

Based on the lightweight characteristics of automotive energy absorption boxes and the requirement of good energy absorption effect, this article first applies the node-enhanced body centered cubic (NBCC) lattice structure to the inner core design of automotive energy absorption boxes. The gradient study of the NBCC lattice structure was carried out using a drop hammer impact and split Hopkinson pressure bar (SHPB). The results indicate that gradient lattice structures have advantages in energy absorption, but there are differences under different gradient strategies. When the impact is not sufficient to compact the structure, the vertical rod diameter gradient node-enhanced lattice structure (RGNBCC) can absorb more energy and improve energy absorption performance by 25%. The vertical height gradient node-enhanced lattice structure (HGNBCC) is more suitable for high-speed impact conditions. Based on the advantages of the RGNBCC in resisting low-speed impacts, it is applied to the inner core design of automotive energy absorption boxes and optimized using multi-objective optimization methods. The optimization results show that the maximum peak impact force is reduced by 45.6% and the specific energy absorption is increased by 30.4%.

Static and dynamic behaviour of aluminium infiltrated ceramic foam at high volume fraction

Ceramics are used in ballistic protection applications for their high hardness and compressive strength; however, they are brittle and shock-sensitive. Co-continuous ceramic composite (C4) infused with a ductile phase can compensate for the brittleness of the ceramic and increase energy absorption with a potential weight reduction in comparison with present multilayer armours. Nevertheless, the research on C4 for armour applications is in its infant stage. This article aims to investigate the energy absorption characteristics of C4 composites with ballistic grade Al5083 infiltrated into different volume fractions of SiC foam (10PPI, 20PPI and 30PPI). The infiltrated C4 samples have 13, 15 and 18 volume percent of SiC in 10PPI-C4, 20PPI-C4 and 30PPI-C4 respectively. The uniaxial compression test of C4 samples revealed that 30PPI-C4 samples have 135 times high compression strength than ceramic preforms and hardness of C4 also enhanced by 13% for 30PPI-C4 samples. The gas gun impact and Split Hopkinson Pressure Bar (SHPB) tests on the 30PPI-C4 specimens reveals that their specific energy absorption (SEA) are 78% and 30% higher than those of 10PPI-C4 and 20PPI-C4 respectively.

Interface Wetting Driven by Laplace Pressure on Multiscale Topographies and Its Application to Performance Enhancement of Metal-Composite Hybrid Structure

Surface topography reconstruction is extensively used to address the issue of weak bonding at the polymer-metal interface of metal-composite hybrid structure, while enhancement from this approach is seriously impaired by insufficient interface wetting. In this study, the wetting behavior of polymer on aluminum surfaces with multiscale topographies was theoretically and experimentally investigated to realize stable and complete wetting. Geometric dimensions of multiscale surface topographies have a notable impact on interfacial forces at the three-phase contact line of polymer/air/aluminum, and a competition exists between Laplace pressure and bubble pressure in dominating the wetting behavior. Laplace pressure facilitates the degassing of trapped air bubbles in grooves, bringing more robust interfacial wettability to grooves than dimples and grids. Conversely, dimples with excessive dimensions generate interfacial pores, and this intrinsic mechanism is theoretically unraveled. Moreover, different degrees of interface wetting cause variations in bonding strength of polymer-aluminum interface, which changes from ∼18% improvement to ∼17% reduction compared to original strength. Finally, groove topography perfectly achieved complete wetting between polymer and aluminum and consequently improved flexure performance by over 11% for the aluminum-carbon fiber hybrid side impact bar, which verifies the importance of complete wetting at a part scale. This study deepens the understanding of wetting behavior and clarifies the intrinsic correlation between interfacial bonding performance and surface topography.

Long-term process stability in additive manufacturing

Laser powder bed fusion (L-PBF), also known as selective laser sintering or direct laser melting, is an additive manufacturing process in which part geometries are formed simultaneously with the underlying material. The microstructure, defect content, and surface quality are all synthesized conjointly with the part shape. While the geometric design freedom allowed by this process enables new complex features and parts with small (∼1 mm) features, challenges associated with process qualification can deter wider adoption. Furthermore, a lack of historical performance data for statistical process control of witness coupons, for either bulk material or for small features, makes the barrier to entry more difficult. Here, we demonstrate long-term, property-based process monitoring and variability assessment using both small-featured (1 mm) and larger, bulk-representative material witness coupons. Over a one-year period, more than 550 tensile bars and 80 Charpy impact bars were printed alongside 316 L stainless steel parts built using L-PBF and tested to detect shifts in the process over time. Miniature tensile bars with a 1 mm2 gage area were tested using a high throughput mechanical testing system. In parallel, a larger test coupon was used to monitor density, hardness, and Charpy impact toughness. This collection of measurements was used to determine detectable property shifts correlated to L-PBF process changes including powder feedstock, machine hardware, software versioning, and machine parameter settings. The benefits of using small featured, high-throughput samples are discussed based on process sensitivity and the number of repeat tests possible for each build. This study not only reveals the utility of property-based process monitoring but illustrates the sensitivity of these measurements to detect process changes and provides further evidence for property stability in modern L-PBF.

Numerical simulation of axially impacted elastic bar

This numerical analysis considers a model of an elastic cylindrical bar impacted by rigid mass, where the accuracy of the model is benchmarked by a closed-form solution developed for this impact process. The analytical solution provides theoretical background and understanding, however, practical problem is not always restricted to a simple one-dimensional geometry and boundary conditions of a purely elastic material behaviour. Hence, the current work numerically simulates the impacted elastic bar, then explores parameters which are not considered in its theoretical model. A two-dimensional (2D) solid axisymmetric system is considered, in which rigid impactor is assigned with initial velocity corresponding to certain drop height and a 2D contact type is defined between interacting bodies. Both elastic and time-dependent viscoelastic material models are considered in this study. The simulation results reveal time intervals gradually increase in every sequential intervals, while relatively small discrepancies are recorded for peak load and pulse width outputs. The parameters of impactor’s mass, drop height and structural stiffness are varied; showing how these parameters individually affect the resulting force response at end struck. The models then evaluate time-dependent viscoelastic material model; showing stiffer response of the resulting force in comparison to models assigned with long-term elastic moduli. Derived elastic modulus-output variable relations show comparable mathematical forms to corresponding equations formulated analytically.

On a bidirectional bending Hopkinson tension test method

In order to achieve bidirectional high strain rate dynamic tension of materials or structures, based on the elastic stress wave propagation theory in bending bars and the principle of the Hopkinson bar, a symmetrical herringbone bending bar was designed. The designed structure can generate and transmit two compression waves at the same time, and convert them into two-way tension waves propagating along the tension bar through the contact adapters. In order to understand the influence of the herringbone bending bar geometric configuration on the propagation of elastic compression waves, the dynamic analysis and ABAQUS finite element analysis (FEA) were carried out for the device. The study shows that after the square compression elastic wave propagates through the bending bar, the platform section of the square wave will incline in high front and low back, and as the bending angle increases, the slope is larger, and the waveform distortion caused by the large curvature rod is more serious. In order to realize the platform segment of the square wave or trapezoidal wave, the tapered impact bar is optimized so that it can be used to generate load waves with low front and high back to offset the tilt distortion in the transmission. In the end, to verify the feasibility and effect of the bidirectional dynamic tensile loading device based on the bidirectional bending Hopkinson bar, a small verification device was built. The results show that the device realized bidirectional tension loading for the pulse width of about 54 μs with good synchronization, the time difference between the starting point of the two waves was less than 2.5 μs, and the amplitude difference was less than 6×10−6. The bidirectional tensile test was carried out on the 2024 aluminum alloy samples, and the good test results were obtained. This confirms that the proposed method can be used for bidirectional dynamic tension and lays the foundation for the expansion of the device to biaxial tensile loading.

Mechanical properties and cushioning mechanism of shear thickening fluid

Shear thickening fluid (STF) is one type of dispersed system with rapidly changing rheological properties under an impulse load. The apparent viscosity of such a suspension system changes dramatically under high-speed impact, and the system can even change from suspension to quasi-solid. Once the load is removed, the STF will quickly return to its original state. In this paper, a mechanical model based on a particle-jammed model and added mass was proposed by calculating the acceleration response of the impact bar, and the local hardening phenomenon of STF in the low-speed impact test was interpreted. Then with the low-speed impact test, the rheological properties of STF in the cushioning process were recorded by a high-speed camera. Meanwhile, a comparison was made with the cushioning efficiency of AV-200, a closed-cell foam material, by using the force-displacement curve. Finally, based on the constitutive relation of STF and by using the fluid-solid coupling method in the FEM, the low-speed impact test of STF was analyzed to obtain more comprehensive dynamic characteristics. The acceleration response obtained in the test was consistent with the theoretical results, which further verified the rationality and effectiveness of the theoretical model. Compared with AV-200, STF has a cushioning efficiency of 50 %–60 %, and its cushioning performance was superior to AV-200. Starting with the rheological cloud map of STF and the acceleration response of the impact bar by the numerical model, a comparison was made with the results of low-speed impact test, and a good agreement is observed.

Experimental Study on Dynamic Compression Mechanical Properties of Aluminum Honeycomb Structures

In this paper, dynamic compression tests are developed to investigate the dynamic compression mechanical properties of the aluminum honeycomb structures at different strain rates, especially at the high strain rates. The difficulties at the high strain rates exist due to the large deformation, the low wave resistance and the size effect of the honeycomb structures. The Split Hopkinson Pressure Bar (SPHB) test method is carried out and special measures such as the adoption of waveform shaper, the size optimization of the impact bar and the specimen, and employment of the semiconductor strain gauge, etc. are taken to overcome the difficulties. It is discovered that the dynamic compression mechanical properties possess a stress hardening effect at a high strain rate from 1.3 × 103 s−1 to 2.0 × 103 s−1, but then a stress softening effect at a high strain rate of 4.6 × 103 s−1. It is also discovered that the yield strength and the average plateau stress at the strain rate of 2.0 × 103 s−1 is higher than that at the strain rate of 1.3 × 103 s−1. However, the yield strength and the average plateau stress at the strain rate of 4.6 × 103 s−1 is lower than that at the strain rate of 2.0 × 103 s−1 and 1.3 × 103 s−1, but higher than that at a quasi-static state. This indicates that the aluminum honeycomb structure is sensitive to the strain rate. Additionally, the damage mode of the aluminum honeycomb structure is plastic buckling, collapse and folding of the cell wall, which is carried out using dynamic compression tests. The folding length of the cell wall at a higher strain rate is found to be longer than that at a lower strain rate. The test results can also be used as the stress–strain curves of the honeycomb constitutive model at the high strain rates to carry out the numerical simulation of high-speed impact.

Simulation of the impact bar top layer tensile test applying the Finite Elements Method

Impact bars represent the main structural components of impact idlers which are used to absorb the impact of the transported material at chutes in belt conveyance systems. An impact bar is a composite comprising three basic structural parts. The top part consists of a polyethylene or polyurethane layer; the middle part is flexible rubber absorbing the dynamic impacts of the falling material; and the lower part is formed from the steel carrying profile. Mathematical modelling of the belt conveyance elements is one of the methods of obtaining relevant results regarding their dynamic load when being impacted by the falling material. The tensile test simulation, performed applying the Finite Element Method, was performed using the Abaqus 6.14 software. On the basis of the true laboratory experimental test, the tension diagram was created and subsequently used as the input for the mathematical model. For the purpose of examination of the plastic behaviour in the Abaqus environment, the logarithmic strain was used and the plastic load zone was demarcated. The elastic zone of relative deformation was determined by the modulus of elasticity. The present article contains the graphical interpretation of the separation of reversible and permanent relative deformations, model geometry, defined material characteristics and boundary conditions, as well as analysis results. The outcome is a high degree of concordance of the results of the laboratory experimental test and the results of the FEM analysis in terms of relative elongation at the breaking point and stress at the breaking point of the tested specimen of the impact bar top layer. The max. difference in the plastic deformation doesn’t exceed 10 %.

Methodology of the Impact Process Applying the Finite Element Method

The economy of material conveyance by pipe conveyors is largely affected by high costs of a conveyor belt and the support system of a conveyor. Even though the operational properties of a conveyor belt are taken into consideration, destruction of the top cover layer and punctures of the whole belt occur rather frequently. The most frequent cause of such damage to a conveyor belt is the impact load at critical sections of the transportation process. Such critical sections, where approximately 60 % of all the damage occurs, include chutes and filling stations. These sections are exposed to the elastic and plastic impact at the moment when the material of a certain weight falls down from a certain height (the maximum allowable impact height is 2.0-2.5 m). The magnitude and the direction of the impact force depend on the structural design of the chute and on the type of the support system. The present article deals with the application of the Finite Element Method (FEM) within the study of the dynamic effects developed at the impact of a load onto the impact bar.

Temperature Effects during Impact Testing of a Two-Phase Metal-Ceramic Composite Material.

Metal-ceramic composite (MCC) materials can be used for manufacturing high-responsibility structures such as jet engines or cutting tools. One example of these materials is a two-phase wolfram carbide (WC) and cobalt (Co) composite. This MCC is a combination of hard WC grains with a Co metallic ductile binder. The resulting microstructure is a combination of two phases with significantly different mechanical behaviors. In this study, we investigate impact conditions, starting with an illustrative example of the Taylor impact bar where—although the process is very rapid—the equivalent plastic strain and temperature are higher in the adiabatic solution than those in the coupled solution. On exposing the WC/Co composite with a metallic binder to impact loading, heat is generated by plastic deformation. If the process is fast enough, the problem can be treated as adiabatic. However, a more common situation is that the process is slower, and the heat is generated in the ductile metallic binders. As a result, the associated grains are heated due to the conduction effect. Consequently, the process should be treated as coupled. When the impact is applied over a short time period, maximum temperatures are significantly lower if the process is analyzed as coupled rather than as adiabatic. The grains are immediately affected by temperature increase in the binders. Therefore, the heat conduction effect should not be omitted.

A miniature multi-pulse series loading Hopkinson bar experimental device based on an electromagnetic launch.

Controlled multi-pulse loading has seldom been applied in classical split Hopkinson pressure bar (SHPB) research. Therefore, a new technique is proposed to realize a controlled multi-pulse loading SHPB experiment, and a miniature multi-pulse series reluctance coil launcher is developed. The micro-multi-pulse series reluctance coil emitter consists of two single-stage reluctance coils and two impact bars. Two loading pulses with the same amplitude are produced by driving the two impact bars to successively impact the incident bar. The distance between the impact bars controls the delay of the second pulse relative to the first one. The delay can be controlled by adjusting the distance between the impact bars and the launch speed. This precise multi-pulse loading technique is easy to implement and can be used to measure and study the dynamic response of various materials in loading SHPB experiments.

HKn-RVEA: a novel many-objective evolutionary algorithm for car side impact bar crashworthiness problem

In this paper, a novel hybrid many-objective evolutionary algorithm, named as hypervolume indicator based on knee point driven and reference vector guided evolutionary algorithm (HKn-RVEA) is proposed. HKn-RVEA is based on the hypervolume indicator, knee points, and reference vector adaptation strategies. The knee points are used to improve the search ability. The reference vectors are used to decompose the optimisation problem into a number of sub-problems. In the proposed algorithm, an adaptation strategy is used to adjust the distribution of the knee points and reference vectors. The proposed algorithm is compared with five well-known evolutionary algorithms over standard benchmark test functions. The results show the performance of HKn-RVEA is better than the competitor algorithms in terms of inverted generational distance (IGD) and hypervolume (HV ) performance measures. HKn-RVEA is also applied to real-life car side crashworthiness problem to demonstrate its efficiency. The experimental results show that the proposed algorithm is able to solve many-objective real-life problems.

HKn-RVEA: a novel many-objective evolutionary algorithm for car side impact bar crashworthiness problem

HKn-RVEA: a novel many-objective evolutionary algorithm for car side impact bar crashworthiness problem

Experiments and Constitutive Modelling of Sand Ejecta Impact

Analysis of the dynamic response of geological porous materials under shock and explosive loading is an important problem in numerous mining and military applications. The experimental characterisation of porous materials with planar shock impact and split Hopkinson pressure bar (SHPB) tests is well developed. However, progress in the test methodology and validation of advanced models is not yet adequate for the complexity of the materials. The present work suggests an experimental set-up aimed at the dynamic observation of momentum transfer from the plume of a porous material ejected by a high explosive (HE) charge. The momentum transfer provides data for model validation and is assessed from the target plate deformation due to impact by the ejecta from a HE charge buried under a layer of a porous material. The porous material used in the paper is represented by calcite sand. An earlier developed two-phase material model for porous materials implemented in the CTH hydrocode is employed for simulating the dynamic behaviour of the calcite sand. The validation experiments are complemented by tailored characterisation experiments for populating parameters within the model which describe (i) the plasticity and compaction behaviour of the sand; and (ii) a kinetic governing shock consolidation transformations within the sand. This includes an analysis of confined SHPB tests and the response of encapsulated sand loaded by HE products in two separate series of tests. The two-phase material model is validated for the calcite sand and comparison with the experimental data demonstrates a good description of the material behaviour.

Comparative experimental investigations on the compressive impact behavior of fiber-reinforced ultra high-performance concretes using split Hopkinson pressure bar

In this paper the compressive impact behavior of steel fiber reinforced ultra-high performance concrete (UHPC) with compressive strengths in excess of 210 MPa was investigated. Different steel fiber volume fractions were used ranging from 0% to 4%. The tested strain rate ranged from 22 to 110 s−1. Based on the obtained results a general equation was developed expressing the dynamic impact factor (DIF) in dependency of the fiber volume fraction. The impact resistance of all UHPC specimens was investigated using a split Hopkinson pressure bar complemented with pulse shaping disks or a shaped striker bar. All analyzed test results were found to satisfy the requirements of dynamic testing such as stress equilibrium, constant strain rate, and reduced friction to minimize inertial effects. A complementary finite element model was developed to simulate the behavior of UHPC specimens under high strain rates. From the results of the finite element analysis it was concluded that the contribution of friction between a greased specimen and the impact bars on the DIF can be neglected. Additionally, UHPC specimens reinforced with 0.5% volume fraction of steel, basalt, or polyvinyl alcohol fibers were tested under dynamic compressive loading at a strain rate of about 40 s−1. The results showed that the slope of the DIF versus strain rate increased with increasing fiber volume fraction. Moreover, UHPC with polyvinyl alcohol fibers was more strain rate sensitive than UHPC with steel and basalt fibers of the same length and volume fraction.

Materials and simulation modelling of a crash-beam performance – a comparison study showing the potential for weight saving using warm-formed ultra-high strength aluminium alloys

Forming complex parts out of high and ultra-high strength aluminium alloys has proved to be more challenging in comparison to the currently used deep drawing steels. The novel “Warmforming-Process” offers the potential to produce light and highly integrated one-piece components out of such aluminium alloys at elevated temperatures. When considering aluminium alloys in the 7000 group, which can reach strength values (UTS) far above 600 MPa, crash components such as side impact bars would offer a suitable field of application.It is important when taking into consideration the geometric design of structural components to utilise their load bearing characteristics in an efficient manner. This structural optimisation lends itself well to computational simulation techniques, which are essential in the evaluation of appropriate geometry and sizing of complex structures with challenging load scenarios.Crash simulations using the nonlinear finite element method (FEM) of side impact protection beams have been used to demonstrate the weight saving potential of high and ultra-high strength aluminium alloys. A beam design formed from a 7000 series alloy was taken as a reference. Substituting various materials, inter alia press hardened steel (phs), and benchmarking against the original beam’s crash performance, by changing the material thickness, equivalent beams were produced.The thicknesses of the beam geometries have been evaluated by “sizing optimisation” and their possible mass reduction are compared against each other. The nonlinear FEM simulations show good agreement with a corresponding set of experimental results. It was seen that for a common crash performance the ultra-high strength aluminium alloys outperform press hardened steel components in terms of their weight. Thus, there is a significant weight saving potential to be realised if crash components are manufactured using 7000 series aluminium alloys. In this work, the weight saving potential was found to be in the region of 20 - 25%.

Sustainable Biocomposites from Pyrolyzed Grass and Toughened Polypropylene: Structure-Property Relationships.

A novel class of injection-molded, toughened biocomposites was engineered from pyrolyzed miscanthus-based biocarbon, poly(octene ethylene) elastomer, and polypropylene (PP). The elastomer and biocarbon were added to the PP matrix at 30 and 20 wt %, respectively. The particle size of the biocarbon varied within two main ranges: <20 and 106–125 μm. The morphology and adhesion between the filler and the matrix were controlled by the addition of maleic anhydride grafted PP (MAPP). The composites were melt-blended and then injection-molded to tensile, flexural, and impact bars. The results showed that although the morphology of the composite is almost independent of particle size it is greatly dependent on the addition of MAPP. Two completely different morphologies, separate dispersion and encapsulated filler particles, were obtained in the presence and absence of MAPP, which was verified by atomic force and scanning electron microscopies. Model calculations based on a modified Kerner equation showed that the encapsulated filler content decreased from 64 to 8% by the addition of MAPP, which caused a major improvement in the stiffness and strength of the composites. Despite having a different morphology caused by the compatibilizer, composites with smaller particles exhibited better strength and modulus and lower impact toughness compared to those with a larger particle size. Results suggest that the failure mechanisms are mainly controlled by the local fracturing of biocarbon particles, which was more pronounced when the particle size was larger.

State-of-the-art in Impact Bar with High Performance

Impact bar is the key part of buffer bed for long distance conveyor equipment which has the characteristics of high energy absorption, low friction, product spillage and scattering elimination. The state-of-the-art and the application of the impact bar and metal matrix composites (MMCs) are introduced. The paper emphatically explained the impact bar structure and integrated process, new theories and computer aided development in the buffer investigation. The main concerns for the impact bar include: structure composition, performance index and key technology; damping technology, laser texturing and genetic algorithm in the simulation and optimization; computer aided design, analysis, testing and manufacturing process in the development of impact bar. Furthermore, the manufacturing standard, quality control and data mining for the impact bar design is urgent to exploited in the future.