Bar Impact Research Articles

Method for measuring rice grain internal damage degree undergoing threshing force

During the threshing process of rice, the grains fall off the head of the rice ear due to the impact of the threshing bar. At the same time, the impact force of the threshing element causes a certain degree of damage to the grain. However, there are relatively few methods to analyze the internal damage of rice grains during the threshing process. In this study, the connection force between rice grains and stalks and the compressive bearing capacity of the grains were tested on a push-pull test machine, and then the critical impact force and velocity of rice grains during plastic deformation and brittle fracture were obtained by Hertz theory. On this basis, the quantitative evaluation model of grain internal damage was established through the extraction and calculation of the damaged area inside the grain, and the damage degrees inside the grain under different loading times and loading forces were analyzed. The results showed that the average threshing force required for rice grains is 1.57 N (variance is 0.0529), and the critical impact forces for plastic deformation and brittle fracture of the grains during threshing are 138.79 N and 145.77 N. Since the threshing force during the threshing process was 43.9-71.9 N, it could be known from the internal damage model that the grain is in the safe loading area. Under the same load, the vertical pressure causes the most damage, the lateral pressure takes second place, and the positive pressure was the least. The results of this study can provide a basis for the development of combine harvester and rice grains damage evaluation. Keywords: threshing process, internal damage of grain, threshing force of roller, plastic deformation, critical impact force DOI: 10.25165/j.ijabe.20211401.5750 Citation: Ren H, Tang Z, Li X Y, Li Y, Liu X, Zhang B, Li Y M. Method for measuring rice grain internal damage degree undergoing threshing force. Int J Agric & Biol Eng, 2021; 14(1): 63–73.

Method for measuring rice grain internal damage degree undergoing threshing force

During the threshing process of rice, the grains fall off the head of the rice ear due to the impact of the threshing bar. At the same time, the impact force of the threshing element causes a certain degree of damage to the grain. However, there are relatively few methods to analyze the internal damage of rice grains during the threshing process. In this study, the connection force between rice grains and stalks and the compressive bearing capacity of the grains were tested on a push-pull test machine, and then the critical impact force and velocity of rice grains during plastic deformation and brittle fracture were obtained by Hertz theory. On this basis, the quantitative evaluation model of grain internal damage was established through the extraction and calculation of the damaged area inside the grain, and the damage degrees inside the grain under different loading times and loading forces were analyzed. The results showed that the average threshing force required for rice grains is 1.57 N (variance is 0.0529), and the critical impact forces for plastic deformation and brittle fracture of the grains during threshing are 138.79 N and 145.77 N. Since the threshing force during the threshing process was 43.9-71.9 N, it could be known from the internal damage model that the grain is in the safe loading area. Under the same load, the vertical pressure causes the most damage, the lateral pressure takes second place, and the positive pressure was the least. The results of this study can provide a basis for the development of combine harvester and rice grains damage evaluation. Keywords: threshing process, internal damage of grain, threshing force of roller, plastic deformation, critical impact force DOI: 10.25165/j.ijabe.20211401.5750 Citation: Ren H, Tang Z, Li X Y, Li Y, Liu X, Zhang B, Li Y M. Method for measuring rice grain internal damage degree undergoing threshing force. Int J Agric & Biol Eng, 2021; 14(1): 63–73.

Study on the Dynamic Response Characteristics of Cylindrical Coal-Rock Samples under Dynamic Loads

To research the dynamic response characteristics of cylindrical coal-rock samples under impact loads, the impact of rigid bars on cylindrical coal-rock samples is simulated under different speed conditions, based on LS-DYNA software, and the dynamic distribution characteristics of the stress, strain, and energy of cylindrical coal-rock samples are analyzed. The results demonstrated the following: (1) the cylindrical coal-rock sample failed at the center first, and the damage developed downward along the axial direction. (2) The critical effective stress and strain have an exponential function relationship with the velocity, and the critical time has a linear relationship with the velocity. (3) The energy change law of the cylindrical coal-rock sample is consistent with the destruction morphology. (4) The axial stress peaks in the severe damage part have a linear relationship with the speed, the axial stress attenuates rapidly after passing the stress yield point, and the axial strain does not increase continuously. (5) The peaks stress and strain on the central axis and the radial line obey the power function distribution, the axial stress produces tensile stress in the axial propagation direction, and the axial stress and strain peaks at the same position are larger than those of the radial stress and strain peaks. This research provides a reference for studying coal and rock dynamic disasters.

Research on Ottosen constitutive model of frozen soil under impact load

Impact blasting loading is an unavoidable problem in cold area construction. In this study, the dynamic characteristics of frozen soil with a water content of 20% and different freezing temperatures are studied under the impact of a spilt Hopkinson pressure bar. Two aspects of the dynamic mechanical response are analyzed to describe the experimental results: temperature rises and the failure mechanism. A rate damage equation is derived considering the improved Ottosen model and thermal activation theory. The experimental results indicate that the improved nonlinear model can be applied to understand the impact mechanics of frozen soil and predict the evolution law of typical mechanical indexes.

Wave Attenuation and Dispersion in a 6 mm Diameter Viscoelastic Split Hopkinson Pressure Bar and Its Correction Method

The propagation characteristics of viscoelastic waves have been investigated with a 6 mm diameter split Hopkinson pressure bar (SHPB) made of polymethyl methacrylate (PMMA). The strain signals in SHPB tests were improved by the pulse shaping technique. Based on the experimentally determined propagation coefficients, the amplitude attenuation and wave dispersion induced by viscoelastic effects at different impact velocities were quantitatively analyzed. The results indicate that the high-frequency harmonics attenuate faster in a higher phase velocity. With an increase in the impact velocity, the amplitude attenuation of the viscoelastic wave changes slightly during propagation, while the waveform dispersion gradually intensifies. A feasible method by waveform prediction was proposed to verify the validity and applicability of the propagation coefficient. The results indicate that the strain obtained from the small diameter viscoelastic SHPB can be effectively modified by utilizing the propagation coefficient. Furthermore, it is preferred to adopt the propagation coefficient obtained at low impact velocity for correction when the impact velocity varies. Moreover, the PMMA-steel bar impact test was performed to further illustrate the accuracy of the propagation coefficient and the effectiveness of the correction method.

Energy-absorption behavior of metallic hollow sphere structures under impact loading

An integrated experimental and computation study is presented of the energy-absorption behavior of metallic hollow sphere structures (MHSS) as an innovative anti-collision material to protect bridge piers from vehicle impact loading. Quasi-static compression and dynamic split Hopkinson pressure bar impact testing were first conducted to compare different deformation and energy-absorption characteristics of MHSS subjected to different loading modes, followed by more realistic laboratory downscaled model impact testing and finite element modeling (FEM) of collisions between real-scale bridge piers and vehicle to further examine the energy-absorption capability of MHSS under dynamic loading. Results show that the MHSS exhibits an increased structural stiffness (e.g., by ~20 times), yield strength (by 4–5 times), and toughness (by 200%) with increasing loading rate (i.e., from static to impact loading). When used as a protective layer on bridge piers, the downscaled model tests and FEM simulations validated the MHSS can provide remarkable anti-collision function to concrete structures: MHSS can substantially reduce the horizontal accelerations (by 63–68%), displacements (by 56.6%), and surface strains of bridge piers, and there reductions further increases with impact velocity. The high energy-absorption capability of MHSS may originates from the exceptionally high, multiscale porosity as well as the excellent mechanical properties of the MHSS material. The findings suggest that MHSS can be an effective energy-absorptive material for anti-collision protection of bridge structures.

Study on the constitutive model of anisotropic aluminum alloy in high speed cutting

In order to construct the constitutive model for high speed machining of aviation aluminum alloy with different forming directions, the Split Hopkinson Pressure Bar (SHPB) impact compression experiment and the high speed orthogonal cutting experiment are carried out in the normal direction (ND), rolling direction (RD) and transverse direction (TD) of aviation aluminum alloy 7050-T7451 rolling sheet. Firstly, the deformation parameters are solved mathematically, and the shear angle, cutting force and cutting temperature are obtained. Subsequently, the initial Johnson–Cook (JC) constitutive model parameters of the material are obtained based on dynamic impact compression experiment. Then, the constitutive model parameters for high speed machining are obtained by modifying the inverse solution program of Oxley orthogonal cutting model. Finally, the modified constitutive model for high speed cutting of aviation aluminum alloy 7050-T7451 rolling sheet considering anisotropy is established. The rationality of the modified JC constitutive model and the accuracy of the results are verified by the finite element simulation.

Fiber reinforced polymer-confined concrete under high strain rate compression: Behavior and a unified dynamic strength model

The behavior of FRP-confined concrete (FCC) under quasi-static compressive loadings is well understood, while the research on dynamic compressive behavior of FCC has hitherto been rarely reported. An experimental program consisting of Split Hopkinson Pressure Bar (SHPB) impact tests and quasi-static compression tests on FCC is conducted and the results are presented in this paper. The strain rate effect on the axial compressive behavior of FCC is studied. Additionally, a new unified dynamic strength model for FCC is proposed and the test results from the current study and the literature are compared with the predictions from the proposed model. Results presented in this research demonstrate that the strain rate effect on impact behavior of FCC is significant and the proposed model can well predict the mechanical properties of the FCC.

Research on the fractal characteristics of the micro/nano-mesoscopic pore structure of high-rank coal under impact loads

ABSTRACT To reveal the mechanism of impact load on coal micropores and improve the extraction efficiency of high-rank coal gas, a separate Hopkinson pressure bar (SHPB) impact test system was used to simulate the shock and stress waves of the impact stress in different attenuation processes. Based on mercury intrusion and low-temperature liquid nitrogen test data before and after impact, fractal theory was applied to study the micropore fractal characteristics of high-rank coal in different directions before and after impact in the Chengzhuang Mine. The results show that pores smaller than or equal to 100 nm based on mercury intrusion data and pores larger than or equal to 100 nm based on low-temperature liquid nitrogen data do not follow fractal rules. Impact loads reduce the seepage and adsorption pore fractal dimensions. Although the seepage and adsorption pore fractal dimensions do not decrease with increasing impact load, a minimum fractal dimension occurs. The impact load corresponding to the minimum seepage and adsorption pore fractal dimensions in the same direction is the same. Impact loads increase gas migration velocities of the seepage pores, reduce the adsorption capacity of the adsorption pores, and promote gas desorption. The research results are important for determining the optimal drainage hole layout and examining the impact cracking and infiltration mechanism.

Turbulent characteristics of flow in the vicinity of mid-channel braid bar

The impact of a mid-channel bar on the turbulent flow structure has been investigated in this research. A new Dominance Function S_(i,H) is proposed in this study as a measure of the relative dominance of ejection and sweep events in turbulent flow structure. Occurrence of the kolk-boil phenomenon is observed due to interaction of ejection and sweep events.. A new parameter Movement Ratio is formulated in this study which is found to faithfully reflect the fluvial processes of sedimentation and scouring on the channel bed.. Acceleration of flow is seen to occur at adjoining regions close to the upstream end of the bar. Due to the presence of the bar, the flow area in its proximity decreases which has caused increment in the velocity at sections located near the upstream end of the mid-channel bar. For model runs with bars, a distinct bulge in the turbulent intensity graph is observed.

Evaluation of traffic behavior in response to alternative police lighting

More than 1500 U.S. law enforcement personnel fatalities occurred from 2007 to 2016, with 39 % of these related to automobile crashes. This study looked at various types of lighting on police vehicles to determine if changes made to the visibility of a police vehicle can impact the surrounding traffic behavior and increase safety for both law enforcement and the general public. Unmarked and marked police vehicles were positioned behind a civilian vehicle on the shoulder of five different multi-lane highways in Virginia, simulating a routine traffic stop. The data collected indicated that more lighting and the use of red in a light bar impact traffic behavior in terms of merging and speed when passing a police vehicle. The benefits may be attributed to the symbolic influence of red as denoting a different type of emergency than a traffic stop in addition to red’s chromatic contrast against the blue sky during the daytime.

Fractal and pore structure analysis of structural anisotropic coal under different impact loads

Pore structure is the key factor that affects the adsorption/desorption of coal. In order to study the change characteristics of pore structure in structural anisotropic coal under different impact loads, the low- temperature liquid nitrogen adsorption tests were carried out after the split Hopkinson bar (SHPB) impact, then the pore structure variation and fractal dimension were calculated and analyzed. The results show that before and after impact, the adsorption isotherms change from type II (raw coal) to type III (impacted coal). With impact loads increasing, adsorption and desorption isotherms change from hysteresis loops to overlap which are determined by open pore structure and dead end pore structure. Meanwhile, mesoporous and micropores in coal samples are much more obviously damaged by larger impact load, and the adsorption capacity becomes smaller, especially for coal samples in parallel to the bedding. Pore volume mainly distribute in mesoporous and macropores, and SSA mainly distribute in mesoporous and micropores. On the whole, the pore volume and SSA decrease with the increase of impact load. Not only pore volume but also SSA in perpendicular to the bedding are larger than that in parallel to the bedding under same impact load. Fractal dimension D2 decreases with impact load increasing, which causes the adsorption capacity linearly reduces.

Confidence-Based Uncertainty Quantification and Model Validation for Simulations of High-Speed Impact Problems

Abstract Validation exercises for computational models of materials under impact must contend with sparse experimental data as well as with uncertainties due to microstructural stochasticity and variabilities in thermomechanical properties of the material. This paper develops statistical methods for determining confidence levels for verification and validation of computational models subject to aleatoric and epistemic uncertainties and sparse stochastic experimental datasets. To demonstrate the method, the classical problem of Taylor impact of a copper bar is simulated. Ensembles of simulations are performed to cover the range of variabilities in the material properties of copper, specifically the nominal yield strength A, the hardening constant B, and the hardening exponent n in a Johnson–Cook material model. To quantify uncertainties in the simulation models, we construct probability density functions (PDFs) of the ratios of the quantities of interest, viz., the final bar diameter Df to the original diameter D0 and the final length Lf to the original length L0. The uncertainties in the experimental data are quantified by constructing target output distributions for these QoIs (Df/D0 and Lf/L0) from the sparse experimental results reported in literature. The simulation output and the experimental output distributions are compared to compute two metrics, viz., the median of the model prediction error and the model confidence at user-specified error level. It is shown that the median is lower and the model confidence is higher for Lf/L0 compared to Df/D0, implying that the simulation models predict the final length of the bar more accurately than the diameter. The calculated confidence levels are shown to be consistent with expectations from the physics of the impact problem and the assumptions in the computational model. Thus, this paper develops and demonstrates physically meaningful metrics for validating simulation models using limited stochastic experimental datasets. The tools and techniques developed in this work can be used for validating a wide range of computational models operating under input uncertainties and sparse experimental datasets.

Phenomena of Adiabatic Shear Bands Forming of Structural Steels Under Impact Load Conditions

Abstract The paper presents the results of an experimental study on adiabatic shear bands (ASB) in two grades of steel with three different microstructures. Samples were subjected to impact forces in order to obtain a targeted shear band. The process of deforming the samples was carried out with a bar impact rod moving at high speeds in the range of 1.4 m/s to 16.5 m/s was carried out. Microstructural studies of deformed samples were performed using the Electron Backscatter Diffraction (EBSD) method. The results of the experiments show that the ASB type depends on the initial microstructure of the material and the deformation speed. It has been shown that, depending on the type of microstructure, ASBs are characterized by a different mechanism of formation and show different character.

Mechanical behavior and texture evolution of WE43 magnesium-rare earth alloy in Split-Hopkinson Pressure Bar and Taylor Impact Cylinder Testing

Mechanical behavior and texture evolution of Mg rare-earth alloy WE43 is investigated for strain-rates 10−3/s to upwards of 105/s for the two material conditions - as-cast (AC) and T6 age hardened, rolled plate (RT6). The high strain-rate behavior is tested using both Taylor cylinder impact tests (TC) and split Hopkinson pressure bar tests (SHB) and bulk textures are obtained using neutron diffraction. Unlike the quasi-static strained material, AC and RT6 SHB retained high hardening rates throughout the test, even up to 30% true strain. Moreover, the high strain-rate data revealed that the RT6 material has a much higher strength than the AC material, but similar hardening rates despite significantly different initial texture. The flow stress near yield increased up to 10% for RT6 and up to 30% for AC as the strain-rate increased six orders of magnitude from quasi-static rates 10−3/s to 103/s. Neither material exhibited significant plastic anisotropy over the broad range of strain rates, despite the fact that the RT6 material had a moderately strong initial texture. In the TC tests, the geometric cross-sectional changes and texture along the cylinder from the cylindrical sample foot to head are measured and from the neutron diffraction texture analysis, upper-bound estimates of twin volume fraction are obtained as well as dislocation density from analyzing diffraction peak broadening. Recorded geometrical changes along several loading directions show that the material has deformed homogeneously under impact. Analysis of deformed textures indicates that {101¯2} extension deformation twinning occurred in the RT6 condition over the range of strain rates, with an upper bound estimate of 40% twin volume fraction for approximately 0.10-0.25 true strain. The peak texture components after the impact have their c-axes closely aligned with the impact direction. These observations are presented and rationalized in the paper.

Dynamic compressive behavior of a novel ultra-lightweight cement composite incorporated with rubber powder

This paper develops a novel rubberized ultra-lightweight high ductility cement composite (RULCC) with added rubber powder and low content PE fiber (0.7%), and investigates the dynamic compressive response and failure mechanism of the RULCC both experimentally and analytically. The test program examines the dynamic compressive stress-strain relationship of the RULCC through Split Hopkinson Pressure Bar (SHPB) impact tests. The results show that the rubber powder aggregates have significant effect on the compressive strength, stress-strain relations and failure mechanism of the RULCC. A volume replacement of fine aggregates with 5%, 10% and 20% rubber power results in a reduction in static compressive strength by 29.5%, 47.7% and 60.3%, respectively. The RULCC with a low fiber content of 0.7% in volume exhibits a 3% direct tensile strain, and a 4–5% tensile strain can still be achieved after 10% rubber powder is added to the RULCC, showing a high ductility of the material. The SHPB impact test shows that the compressive strength increases with strain rate. An empirical model, taking into account of the replacement ratio of the rubber powder aggregates in the RULCC, is developed in this paper to evaluate the Dynamic Increasing Factor (DIF). The experimental and analytical studies are essential to better understand the fundamental dynamic behavior of the RULCC for its further applications in engineering applications, such as protective structures, etc.

Dynamic responses of hybrid lightweight composite sandwich panels with aluminium pyramidal truss cores

This paper experimentally and numerically investigates the free vibration, quasi-static compressive and split Hopkinson pressure bar impact responses of hybrid composite pyramidal truss sandwich panels. Such sandwich panels made of carbon fibre composite face sheets and aluminium alloy pyramidal truss cores are fabricated using an interlocking and adhesive bonding approach. Modal tests and quasi-static compression tests are conducted. A good consistency for natural frequencies, modal shapes and static stress–strain curves of the specimen with the same specification is obtained, which ensures the good repeatability of the present specimens. Considering the effect of strain rate, a series of split Hopkinson pressure bar tests combined with numerical simulations is carried out to investigate their dynamic compression responses. A good agreement between simulation results and experimental data is observed, which shows that the adopted split Hopkinson pressure bar testing device and the modified Johnson-Cook model are reasonable and reliable. Results show that the dynamic compression modulus and strength of specimen are strongly influenced by the relative density of the truss cores and much higher than the corresponding static compression modulus and strength. Furthermore, it is also revealed that all the specimens have excellent energy absorption performance, which may have greatly advantage in shock isolation application.

Strain rate effect on dynamic mechanical properties and microstructure of cemented tailings composites

The dynamic mechanical properties of the cemented tailings composites (CTC) is one of the major technical challenges in the mining engineering field. In this paper, the Split Hopkinson Pressure Bar (SHPB) impact loading and scanning electron microscopy (SEM) system were conducted to investigate the average strain rate (ASR) rate on the dynamic compressive strength (DCS), microstructure fractal dimension and failure pattern of the CTC specimens. The result shows that the DCS of the CTC increased exponentially with the increase of ASR value when the ASR was in the range of 10–100 s−1. The main hydrate productions of CTC are C-S-H and AFt. The pore size of CTC increased with increased ASR. The fractal dimension of the pore area increased linearly with increased ASR. According to the above results, it provides a reference for engineers of mine sites to reduce the blasting impact load utilizing discontinuous charging and differential detonation, thus achieving the goal of reducing the dilution rate of underground mining.

Influence of Support Structures on the Microstructure and Mechanical Properties of Case Hardening Steel in Laser Powder Bed Fusion

Additive manufacturing, especially laser powder bed fusion (LPBF), enables the manufacturing of complex and lightweight parts. LPBF is a technology with high geometric degrees of freedom, but there are production restrictions, e.g., with regard to overhangs. One strategy to produce these components despite the restrictions is the use of support structures. After the LPBF process the support structures are removed by hand or through machining before general post-processing, e.g., manufacturing of functional surfaces or heat-treatments are concluded. However, support structures change the local process conditions during LPBF depending on the parts geometry (no support structures vs. use of support structures). The influence is mainly caused by the changed heat dissipation of the support structures compared to dense part material. In this contribution, the influence of support structures on the resulting microstructure and the mechanical properties are determined for the case hardening steel 16MnCr5. Case hardening steels are used for gearings and pinions for wide applications in the aerospace industry, e.g., engine gear boxes for helicopters or UAVs (unmanned aerial vehicles). It can be seen that the height of the applied support structures has great influence on the microstructure. Mechanical properties are determined through notched bar impact testing showing an increase in toughness in the as-built state with increasing support structure height. The findings correspond with the increasing content of ferrite seen in the microstructure. The effect of subsequent heat treatments (stress relief annealing and case hardening) on the mechanical properties is also investigated. Furthermore, generalized operating principles for the influence of support structures and the occurring insitu heat treatment in LPBF are presented and described based on the results shown.

Effect of Porosity on Dynamic Mechanical Properties and Impact Response Characteristics of High Aluminum Content PTFE/Al Energetic Materials.

In order to obtain the effect of porosity on the dynamic mechanical properties and impact response characteristics of high aluminum content PTFE/Al energetic materials, PTFE/Al specimens with porosities of 1.2%, 10%, 20%, and 30% were prepared by adding additives. The dynamic compression properties and impact response characteristics of high aluminum content PTFE/Al energetic materials with porosity were studied by using a split Hopkinson pressure bar (SHPB) impact loading experimental system. Based on the one-dimensional viscoplastic hole collapse model, an impact temperature rise analysis model including melting effects was used, and corresponding calculation analysis was performed. The results show that with the increase of porosity, the yield strength and compressive strength of the material will decrease. Under dynamic loading, the reaction duration of PTFE/Al energetic materials with different porosities generally shows a tendency to become shorter as the porosity increases, while the ignition delay time is basically unchanged. In this experiment, the material response has the optimal porosity with the lowest critical strain rate, the optimal porosity for PTFE/Al energetic materials with different porosity and high aluminum content (50/50 mass ratio, size of specimens Φ8 × 5 mm) is 10%. The research results can provide an important reference for the engineering application of PTFE/Al energetic materials.