Drop-weight Test Research Articles

Optimization of multiple collision characteristics using an innovative crashworthiness diagram

As the crashworthiness and weights of parts in vehicles are both directly influenced by the thickness of the corresponding materials, a reasonable compromise is required for the optimal design. In this study, an innovative crashworthiness diagram was proposed for optimizing the multiple collision characteristics of automobile components with respect to thickness. The crashworthiness diagram was designed to consider multiple collision characteristics, such as the impulse, energy absorption, and anti-intrusion displacement, based on a crashworthiness index (CI). The respective CI values were assessed both analytically and numerically to determine the optimal thickness of an alternative material. The use of aluminum alloys was investigated, aiming to improve the collision resistance while ensuring lightness. Based on the crashworthiness diagram, an Al7075-T6 bumper beam with a thickness of 2.5 mm was used to replace a 22MnB5 (HPF) bumper beam with a thickness of 1.4 mm. An experimental validation of the Al7075-T6 bumper beam through a drop-weight test confirmed that the proposed crashworthiness diagram is a feasible and reliable guide to determine alternative material with target collision resistance

Failure Modes of Reinforced Concrete Beams Strengthened in Flexure with Externally Bonded Aramid Fiber-Reinforced Polymer Sheets under Impact Loading

This paper focuses on the aramid fiber-reinforced polymer (AFRP) sheet bonding method to investigate the influences of the sheet volume and input impact energy on the failure modes of strengthened RC beams. The drop-weight impact loading tests were conducted on RC beams strengthened with AFRP sheets. The sheet volume was investigated, varying from 415 to 1660 g/m2. The impact force was generated by dropping a 300 kg steel weight onto the midspan of the beams from different heights (0.5, 1.0, 2.0, 2.5, 3.0, and 3.5 m), and the weight’s drop height was raised until the sheets were debonded or ruptured. As a reference beam, nonstrengthened beams were also evaluated. The following are the findings of this research. (1) In the event of impact loading, the impact resistance capacity of strengthened beams can be enhanced by up to 85% by applying the AFRP sheet bonding method; however, (2) in the case of relatively large impact energy, the impact resistance capacity may not always be remarkable. (3) Depending on the sheet volume, the failure mechanism of the AFRP-strengthened beams was classified into two types: sheet debonding and sheet rupturing. Furthermore, (4) increasing the sheet volume may not improve the debonding of the AFRP sheet of the strengthened beams.

고감도 유연 마찰전기 센서 제작을 위한 유전분극 특성 향상에 관한 연구

A novel method for the development of a highly sensitive triboelectric sensor based on porous PDMS matrix and carbon black (CB) particles is proposed. The porosity of the PDMS is controlled by using wet sugar particle sizes, and we fabricate a porous PDMS plate with a pore-to-volume ratio of 46%, which has a larger internal contact area compared to a non-pore one. To investigate the sensitive responses of the sensor, two key processes for the deposition of CB particles are conducted. One is the stirring process and another is ultrasonic vibration waving process. Based on the proposed method, a high-performance flat triboelectric sensor is fabricated. By a weight drop test of two different sensors, the amount of out-voltage is changed to approximately 29.1 and 95.1%, respectively. Through this study, we can evaluate that the sensitivity of triboelectric sensors is affected by the deposition method of the CB particles. The proposed flexible triboelectric sensor can be applied to analyze human physical behavior. Also, we believe that it can be applied to measure various physical signals such as contact force or gripping force with small values.

Impact properties of modified 9Cr 1Mo steel welds: Comparison between cold wire and hot wire gas tungsten arc welding processes

Modified 9Cr 1Mo steel is used for the manufacture of Steam Generators (SG) for Prototype Fast Breeder Reactor at Kalpakkam, India. The hot wire Gas Tungsten Arc Welding (GTAW) process was selected for the manufacture of SGs wherever feasible in addition to the conventional cold wire GTAW process due to various advantages. Drop weight tests on modified 9Cr 1Mo steel welds produced by hot wire and cold wire GTAW processes were carried out in accordance with ASTM E208. It is found that the Nil Ductility Transition (NDT) behavior of the hot wire and cold wire GTA welds were similar during drop weight tests performed up to −10 °C. Subsequently, Charpy V notch impact tests were carried out at +18 °C and 0 °C in accordance with ASME Boiler and Pressure Vessel Code. The impact strength at 0 °C of welds produced by cold wire GTAW process was found to be superior compared to the welds of hot wire GTAW process. Subsequently, the analysis of impact strength was carried out using a two-sided students t-test. With a 95% confidence level, the results of the t-test revealed that there is a genuine difference in impact strength at 0 °C between the welds of hot wire and cold wire GTAW processes.

An extended peridynamic model for dynamic fracture of laminated glass considering interfacial debonding

In this work, an extended peridynamic (PD) model considering interfacial debonding is proposed to investigate the dynamic fracture behavior of laminated glass under low-velocity and high-velocity impacting loads. The interaction between different materials is described by adding an interfacial force term into the governing equations, which is derived from the energy density function of the interfacial bonds. A potential function term sourced from the cohesive zone model (CZM) is reconstructed and then introduced into the peridynamic model to describe the cohesive interfaces. The failure criterion of interfacial debonding is determined by the calculation of interface fracture energy and interfacial energy density. Two benchmark examples, a through-cracked tensile test and a drop-weight test, have been conducted to establish the validity of the proposed model. The proposed model and approach are then employed to investigate the dynamic fracture mechanism of laminated glass under high-velocity impacting loads.

Functional Anatomy, Impact Behavior and Energy Dissipation of the Peel of Citrus × limon: A Comparison of Citrus × limon and Citrus maxima.

This study analyzes the impact behavior of lemon peel (Citrus × limon) and investigates its functional morphology compared with the anatomy of pomelo peel (Citrus maxima). Both fruit peels consist mainly of parenchyma structured by a density gradient. In order to characterize the lemon peel, both energy dissipation and transmitted force are determined by conducting drop weight tests at different impact strengths (0.15–0.74 J). Fresh and freeze-dried samples were used to investigate the influence on the mechanics of peel tissue’s water content. The samples of lemon peel dissipate significantly more kinetic energy in the freeze-dried state than in the fresh state. Fresh lemon samples experience a higher impulse than freeze-dried samples at the same momentum. Drop weight tests results show that fresh lemon samples have a significantly longer impact duration and lower transmitted force than freeze-dried samples. With higher impact energy (0.74 J) the impact behavior becomes more plastic, and a greater fraction of the kinetic energy is dissipated. Lemon peel has pronounced energy dissipation properties, even though the peel is relatively thin and lemon fruits are comparably light. The cell arrangement of citrus peel tissue can serve as a model for bio-inspired, functional graded materials in technical foams with high energy dissipation.

Stiffness and damping properties of railway ballast aggregate considering influence of degradation of aggregate and incorporation of crumb rubber

Impact loads over ballasted railway tracks can accelerate ballast aggregate degradation and deformation. The incorporation of energy-absorbing materials is a practical method to improve the stiffness and damping characteristics of granular layer and diminish aggregate degradation. This study investigated the dynamic responses of ballast aggregates subjected to the drop-weight impact loading test to further illuminate the effect of loading conditions and crumb rubber (CR) incorporation on the stiffness and damping coefficients of ballast material. Experimental measurements were combined with the analytical approach to link the aggregate degradation level to energy evolution and characterize the relationship between the induced impact load and the dynamic properties of granular material. The results demonstrated that the damping properties of ballast material decreased as the number of loading steps increased, which is mainly attributed to further aggregate degradation. The experimental-analytical analysis corroborated lower stiffness and higher damping coefficient for CR-reinforced mixtures. Smaller CR particles led to greater energy dissipation. A linear relationship was also found between the breakage level of aggregates and the energy induced due to friction development between particles and individual aggregate breakage.

Investigation of dolomite’ rock brittle fracture using fully calibrated Karagozian Case Concrete model

This paper presents a procedure to compute the parameters of the Karagozian and Case Concrete (KCC) constitutive model for brittle materials based on dolomite rock. First, the fracture energy and fracture toughness of the dolomite rock were determined from two experimental tests: the semicircular bending test (SCBT) and Brazilian indirect tension test (BT). Next, the novel optimization-based strategy was developed for efficiently calibrating the brittle damage parameters, and a broad parametric study was performed based on dolomite rock. Finally, the optimal parameters were validated through three experimental tests: SCBT, BT and a drop-weight fragmentation test. The results were compared with those obtained using three different sets of parameters for dolomite rock that is the KCC model with automatically generated parameters, parameters that provides an instable softening behavior, and the KCC model with parameters calibrated by the authors in a previous study. A qualitative and quantitative comparison of the results confirmed that the approach presented here improves the efficiency of fracture reproduction.

Finite element modelling of low velocity impact test applied to biaxial glass fiber reinforced laminate composites

• High-speed imaging and DIC are used to track damage progression during impact test • A proposed 3D FE model allows predicting the impact behavior of laminate composites • [0/90] 3s laminates failed due to fiber breakage at high compression impacted region • [±45] 3s laminates exhibited matrix cracking and delamination caused by high tension The aim of this paper is to describe the dynamic behavior of biaxial glass fiber reinforced laminate composites under low velocity impact test through finite element modelling. Experimental investigations by impact test performed using an instrumented drop weight testing machine were conducted on three-point bending composite samples in order to assess their impact damage resistance. Moreover, the experimental setup allowed the visualization of real-time damage progression of the impacted laminate composite via high-speed camera Phantom V2512 enabling to capture 83000 frames per second. Dynamic strain fields were extracted by Digital Image Correlation (DIC) method. Based on the experimental results, a numerical study of the impacted specimens was developed as a user subroutine VUMAT integrated to ABAQUS/Explicit in order to precisely capture the progressive dynamic failure of the laminate composite under impact test. In the proposed model, the damage and failure of each ply are accounted by a Hashin 3D damage-based behavior, and a cohesive zone model is employed to capture the onset and progression of inter-laminar delamination. A good experimental-numerical correlation was obtained for peak force and failure modes.

Impact resistance of porosity-free fiber-reinforced concrete (PFFRC) beams under low-velocity impact loading

Ultrahigh-performance fiber-reinforced concrete (UHPFRC) is an advanced cement-based composite material. Its ultrahigh compressive strength and high ductility can enable the downsizing of structural members, with special application to high-rise buildings. These excellent mechanical properties also allow its application in protective structures to resist high-speed penetration, low-velocity impact, and blast loading. UHPFRC with a compressive strength of approximately 150–200 MPa has traditionally been used to investigate the impact resistance of structural members under low-velocity impact loading. Recently, however, porosity-free concrete of the 400 MPa class of compressive strength has been developed. In this paper, to investigate the effects of the concrete strength and the steel fiber volume fraction on the impact resistance of porosity-free fiber-reinforced concrete (PFFRC) members, static and drop-weight impact loading tests were conducted on PFFRC beams by varying the volume fraction of steel fiber from 1 to 3.5%. As reference beams, 90 MPa high-strength fiber-reinforced concrete (HSFRC) beams with a 2% fiber volume fraction and normal-strength concrete (NSC) beams without stirrups and steel fibers were also tested. The results obtained from this study were as follows: (1) the static load-carrying capacity of a PFFRC beam can be enhanced by more than two and three times that of an NSC beam by adding 1 and 3.5% volume fractions of steel fiber, respectively; (2) a PFFRC beam with 3.5% fiber had the greatest impact resistance of all the beams considered in this study, and the beam with 2% fiber volume had the second-greatest performance, but the difference was small; (3) even though an HSFRC beam with 2% fiber had a smaller static load-carrying capacity than a PFFRC beam with 1% fiber, the former exhibited a slightly greater impact resistance than the latter because the bridging effect of the steel fibers has a greater influence under impact loading than under static loading.

Experimental determination of sectional forces in impact tests: Application to composite RC-HPFRCC beams

The impact response of concrete structures differs significantly from the quasi-static behaviour due to strain rate influence on mechanical properties, formation of inertia forces and local damaging mechanisms. The time-variable acceleration of the impacted element leads to inertia forces which produce a time-dependent distribution of shear forces and bending moments. The failure mode of impacted elements is significantly affected by the distribution of sectional forces and a detailed study of such forces is therefore convenient for a full understanding of impact mechanics. One of the most extended approaches to study experimentally the impact behaviour of reinforced concrete (RC) beams is with the help of instrumented drop weight testing machines. Such facilities usually incorporate dynamic load cells to measure the support reactions and the impact force. Though the resulting inertia force can be derived by difference of reactions and impact force, its distribution cannot be determined, which is necessary for the estimation of sectional forces. In the present paper, an experimental methodology based on digital image correlation (DIC) supported by a high-speed and high-resolution camera is presented. The proposed methodology provides an accurate estimation of inertia forces which allows deriving the time-dependent evolution of shear forces and bending moments. The methodology is applied to an experimental campaign consisting of RC beams strengthened with a thin layer of high-performance fiber-reinforced cement composite (HPFRCC). The impact response of composite RC-HPFRCC elements is analyzed by examining the shear forces and bending moments at the critical sections. The implemented DIC-based methodology allows understanding the critical instants of the tests which lead to shear cracking. Moreover, a shear strength model is presented to estimate the capacity of studied RC-HPFRCC elements.

Impact Resistance of Styrene-Butadiene Rubber (SBR) Latex-Modified Fiber-Reinforced Concrete: The Role of Aggregate Size.

Improvements in tensile strength and impact resistance of concrete are among the most researched issues in the construction industry. The present study aims to improve the properties of concrete against impact loadings. For this purpose, energy-absorbing materials are used along with fibers that help in controlling the crack opening. A polymer-based energy-absorbing admixture, SBR latex, along with polypropylene fibers are used in this study to improve the impact resistance. Along with fibers and polymers, the effect of the size of aggregates was also investigated. In total, 12 mixes were prepared and tested against the drop weight test and the Charpy impact test. Other than this, mechanical characterization was also carried out for all the 12 concrete mixes. Three dosages of SBR latex, i.e., 0%, 4%, and 8% by weight of cement, were used along with three aggregates sizes, 19 mm down, 10 mm down, and 4.75 mm down. The quantity of polypropylene fibers was kept equal to 0.5% in all mixes. In addition to these, three control samples were also prepared for comparison. The mix design was performed to achieve a normal-strength concrete. For this purpose, a concrete mix of 1:1.5:3 was used with a water to a cement ratio of 0.4 to achieve a normal-strength concrete. The experimental study concluded that the addition of SBR latex improves the impact resistance of concrete. Furthermore, an increase in impact resistance was also observed for a larger aggregate size. The use of fibers and SBR latex is encouraged due to their positive results and the fact that they provide an economical solution for catering to impact strains. The study concludes that 4% SBR latex and 0.5% fibers with a larger aggregate size improve the resistance against impact loads.

Influence of geometry constraint in finite space on impact resistance of shear thickening fluid

The shear thickening area formed by impact load and the restriction boundary conditions play an important role in the impact resistance and energy absorption characteristics of the shear thickening fluid (STF). In order to reveal the low speed impact resistance of STF under finite space constraints, this paper carried out research through the preparation of STF, viscosity test and design of low speed drop weight impact experiment. Firstly, STF samples with different mass fractions were prepared by self-made. Then, the rheological tests were implemented to obtain the characteristics of STF viscosity under different shear rate loads. Next, a straightforward test through rapidly pulling the glass rod out of the STF was adopted to observe the shear thickening mechanism of STF. After that, two kinds of STF samples with different mass fractions and good shear thickening performance were selected for low speed drop weight test. In the drop weight test, three containers with different geometries were designed to equivalent the finite space constraints to reveal the low speed impact resistance of STF under finite space constraints. Finally, combined with the experimental results, a series of numerical models are established to study the influence of geometric parameters in finite space on the impact resistance of STF. Through the research of this paper, the influence of geometry constraint in finite space on impact resistance of STF was obtained, which can provide reference for the geometric design of protective structure filled with STF.

Low-velocity and ballistic impact resistances of particle reinforced metal–matrix composites: An experimental study

This study investigates the low-velocity and ballistic impact responses of SiC-reinforced Al6061 metal–matrix composites in different reinforcement volume fractions. Low-velocity impact (LVI) tests were performed with samples having SiC particle volume fractions of 0, 5, 10, 15, 20, 30, and 40%, while ballistic tests were carried out with samples having volume fractions of 0, 10, 20, and 30%. The weight-drop test method was used for LVI by applying 50 J (4.45 m/s) energy to all samples. Ballistic tests were carried out under the same conditions on all samples with the projectile launched at an average velocity of 500 m/s. For the determination of the ballistic resistance of the samples, the projectile penetrations in the witness structures were taken into consideration. The damage and deformations caused by both the LVI and the ballistic test in composites were examined. By the LVI test results, composite samples have absorbed less impact energy by increasing the reinforcement volume fraction, as well as demonstrated superior performance compared to unreinforced samples. In addition, the crack formation was mainly observed in the samples containing 30% reinforcement, while the composite material with a 40% volume fraction was completely broken. With the increase in the reinforcement volume fraction, the ballistic resistance of the samples increased significantly.

Numerical Simulation of a Single and Double-Rotor Impact Crusher Using Discrete Element Method

The Discrete element method (DEM) is an invaluable tool for studying comminution as it provides detailed information that can help with process analysis as well as trying out new equipment designs before the equipment is physically built. The DEM was used to analyse previous experimental work to gain some insight into the comminution process in an impact crusher with a single impeller. Further DEM simulations were done on a crusher with a second impeller installed. The energy spectra and threshold energy levels calculated from the drop-weight test were used as the basis of comparison. The simulations indicate that even at much lower speeds, the performance of a double impeller impact crusher is exceedingly superior. However, the energy associated with the double impeller impact crusher is much higher and energy intensification, rather than energy efficiency, is the main gain of the double impeller design. The double impeller also offers more operational flexibility, such as spacing between the impellers, which can be tailored to the particle size range being handled.

Investigations on the Response of Novel Layered Geopolymer Fibrous Concrete to Drop Weight Impact

In recent years, geopolymer concrete (GC) has become more popular in construction because of its multiple benefits, such as eco-friendliness, high temperature resistance and resistance to chemical attack in harsh environments. However, GC has limited deformation capability and tensile strength compared to ordinary concrete. Geopolymer fibrous concrete (GFC) exhibits high mechanical properties, such as compressive strength and impact strength. This study aimed to develop a novel composite comprising GFC at the tension zone and GC at the compression zone, and vice versa, are these composites were examined. The impact resistance of two-layered GC-GFC with various ratios (25–75, 50–50, 75–25%) was examined. In addition, a single layer specimen comprising GC and GFC was fabricated and tested as the reference specimen. Twenty-nine mixtures were developed and divided into four series. Four different types of fibre were used in this study; short polypropylene fibre, long polypropylene fibre, short steel fibre and long steel fibre. The ACI committee 544 drop weight test was used to evaluate the impact strength of specimens. Results indicated that the impact strength of GFC was significantly improved in long steel fibre-based specimens. In addition, two-layered specimens comprising different fibres—short polypropylene, long polypropylene, short steel and long steel—exhibited a positive influence on impact strength. Compared to a single-layer specimen, inferior impact strength was recorded in the two-layered specimen.

Performance of reinforced concrete beam with cushion subjected to impact loading

Many countries are developing new ways to protect Reinforced Concrete (RC) structures under specific risks such as rockfall hazards. Cushioning materials, for example, are using to improve the impact resistance of the RC structures. Applying cushions improves the strength of RC structures under aging of materials and deteriorations, therefore, it improves the safety of people, buildings, and infrastructure systems. However, the impact resistance of RC structures with cushions have not yet been clarified. This study aims to clarify the effect of four types of high strength expanded materials, three are Polystyrene and one is Polycarbonate, which were set on RC beams to enhance impact resistance of the beams. Drop weight tests were employed to investigate the mechanical behavior of RC beams with cushions. The following conclusions were found based on the results of this study: 1) High energy absorbing cushions should be used to protect RC beams subjected to impact loadings as it significantly reduced the maximum deflection and crack opening process of the beams. 2) The hardening effect of concrete at upper cover surface of RC beam during collision were confirmed by using yielding static test. It is used to calibrate static fiber model of normal RC beam to obtain the maximum deflection due to impact loadings. 3) The impact absorbing energy of the cushions were verified to establish simplified equation of maximum deflections of the beam with cushions. 4) The estimated maximum deflections of RC beams with and without cushions are in agreement with the measured values.

Mechanical Properties of Clayey Soil Reinforced with PET Considering the Influence of Lime-Stabilization

Reusing waste plastic can be considered as an important issue in terms of economical as well as environmental concerns. Stabilization of clayey soil is a well-utilized approach to improve the mechanical properties concerning the geotechnical aspects. Meanwhile, the effect of concurrent employment of both lime and waste plastic fibers with different contents and various shapes on mechanical properties of clay is not evident. This research presents the mechanical characteristics of clayey soil reinforced with Plastic Polyethylene Terephthalate (PET). Both unstabilized and lime-stabilized clay are considered as unreinforced materials and the plastic strips and pellets are separately utilized as reinforcement substances. Various tests namely standard Proctor compaction test, point load test (PLT) and drop-weight impact loading test are performed to assess the effect of reinforcement and stabilization on mechanical behavior of clayey soil. The concurrent influences of using PET and adding lime confirm that positive effect of lime stabilization on strength is more meaningful. Meanwhile, the limited content of 1.5% of PET shows the maximum strength for reinforced clayey soil. Generally, reinforcement with strips leads to the exhibition of higher strength based on the point load strength index and more flexibility based on the applied impact loads in comparison with pellet particles.

Investigation on thermal characteristics and desensitization mechanism of improved step ladder-structured nitrocellulose

Nitrocellulose, or cellulose nitrate, has received considerable interest due to its various applications, such as propellants, coating agents and gas generators. However, its high mechanical sensitivity caused many accidents during its storage and usage in ammunition. In this work, two kinds of insensitive step ladder-structured nitrocellulose (LNC) with different nitrogen contents were synthesized. The products were characterized by FT-IR, Raman, XRD, SEM, elemental analysis, TGA, DSC, accelerating rate calorimeter analysis (ARC), and drop weight test to study their molecular structure, thermal characteristics and desensitization performance. Compared with raw nitrocellulose, LNC has a sharper exothermic peak in the DSC and ARC curves. The H50 values of the two kinds of LNC increased from 25.76 to 30.01 cm for low nitrogen content and from 18.02 to 21.84 cm for high nitrogen content, respectively. The results show that the ladder-structure of LNC which provides regular molecular arrangement and a soft buffer made with polyethylene glycol could affect the energy releasing process of LNC and reduce the sensitivity of LNC. Insensitive LNC provides an alternative to be used as a binder in insensitive propellants formulation.

Comparison of the mechanical properties of chopped glass, carbon, and aramid fiber reinforced polypropylene

In this work, a comparative assessment of the mechanical properties of chopped glass-carbon-aramid fiber reinforced polypropylene (PP) composites was carried out. Reinforcement and matrix materials were mixed with the extrusion method, and then composite materials were produced in the form of plates with the press molding technique. The composites' tensile, 3-point bending, and drop weight tests were carried out and the surface morphology of the fractured surfaces was examined by Scanning Electron Microscope (SEM). The tests’ results indicate that the mechanical properties increase significantly in the presence of fiber. On the other hand, it is observed that the effect in percentage decreases as the fiber content increases. Moreover, It was observed that some of the fiber materials were pulled out from the matrix as a result of stress. ANOVA analysis using S/N values, and F-Test were performed to observe the effectiveness of each test factor (fiber type, and fiber additive content) on the test results. Finally, an optimization study was carried out to obtain the mathematical expression by fitting the experimental data.