Drop Hammer Test Machine Research Articles

Evaluation of measurement uncertainty of drop hammer impact test for composite materials

Future aircraft structures are usually dominated by composites, and one of the key defects and forms of damage to composite structures is the impact damage caused by low-energy (especially low-speed) foreign matter. This kind of low-energy impact test is usually completed by the drop hammer testing machine, so accurately assessing the impact test of the falling hammer completed in accordance with the standard test method, and the reliability of the permissible value of the impact performance of the objective reaction composite is of great significance to the future aircraft structure design. Taking a standard composite test piece as an example, considering the key factors in the whole process of impact test, a mathematical model is constructed, and the measurement uncertainty of different configuration composite test pieces of different configurations is calculated according to the test data, which provides a basis for aircraft structural design.

Low-velocity impact failure of foam-filled GFRP trapezoidal corrugated sandwich structures

In this paper, a new lightweight sandwich structure with polyurethane foam filled glass fiber reinforced polymer (GFRP) trapezoidal corrugated sandwich structure is fabricated. Based on the low-velocity impact tests, the impact failure performance and energy absorption efficiency of polyurethane foam filled sandwich structures are investigated. Low-velocity impact tests were carried out on the node and base positions of the foam filled trapezoidal corrugated sandwich structure by using a drop hammer test machine, and the set impact energy range was 25 J – 150 J. Experimental results show that when the impact energy is the same, the maximum impact load and maximum energy absorption generated by the node impact are greater than the base impact, which proves that the node position has better impact resistance and energy absorption effect than the base position. In addition, by comparing the displacement-time curves of foam filled and unfilled sandwich structures, it is found that when the impact energy is the same, the slope of the displacement-time curve of unfilled specimen is greater than that of foam filled specimen. Therefore, within the same time, the deformation of unfilled specimen is larger than foam filled specimen during the impact process, which demonstrates the effectiveness of polyurethane foam filling on the gain of sandwich structure.

Impact response of lightweight steel foam concrete composite slabs: Experimental, numerical and analytical studies.

This paper presents a study on the low-velocity impact response of lightweight steel foam concrete (LSFC) composite slabs. The LSFC composite slab consisted of a W-shaped steel plate, foam concrete and oriented strand board (OSB). Low-velocity impact tests on the LSFC composite slabs were conducted by employing an ultra-high heavy-duty drop hammer testing machine. The tests revealed the failure mode, impact force and displacement response of LSFC composite slabs. The effects of density and thickness of foam concrete and drop height on the peak impact force and energy absorption ratio were investigated. A finite element (FE) model was set up to predict the impact resistance of the LSFC composite slabs, and a good agreement between simulation and test results was achieved. In addition, an equivalent-single-degree-of-freedom (ESDOF) model was set up to predict the displacement response of the LSFC composite slabs under impact loading.

Failure mechanism and impact resistance of a novel all-composite double-corrugated sandwich plate under low-velocity impact

A novel composite double trapezoidal corrugated sandwich plate (CDTCSP) was prepared by mold hot pressing and secondary bonding of carbon fiber reinforced polymer (CFRP) prepregs. The DIT302E drop hammer testing machine with a hammerhead of 5.5 kg was selected to realize the impact test of the new corrugated sandwich structure and the all-composite trapezoidal corrugated sandwich plate (CTCSP) with three different energies of 10 J,30 J, and 50 J by changing the height. The failure modes of the two samples were further studied by experimental investigation along with the finite element model established in Abaqus/Explicit. Based on the verified numerical model, the failure process of CDTCSP under 30 J and 50 J impact energy is analyzed. At the same time, the effects of different impact positions and layup angles on the impact resistance of CDTCSP at 10 J energy were evaluated. It can be observed that as the impact energy increases, the peak load of the composite corrugated sandwich plate decreases. Compared with the traditional ones, the impact position has no noticeable effect on the overall impact resistance of CDTCSP. Based on the analysis of CDTCSP with five different layup parameters, it is found that the matrix compression failure extends along the fiber direction, and the peak load of the sample with all the surfacing layup of ± 45° is 17% larger than that of the sample with 0°.

Impact resistance of single-cell and multi-cell sandwich aluminum plates filled with aluminum foam

The aim of this paper is to investigate the impact resistance and energy dissipation capacity of a new type of multi-cell sandwich aluminum alloy plate filled with aluminum foam, in comparison to the single-cell structure. To achieve this goal, 30 sandwich aluminum alloy plates were tested using a drop hammer test machine, varying impact velocity, wall thickness, and the number of internal diaphragms. The results were analyzed and finite element analysis was conducted to explore the energy dissipation mechanisms and the effect of aluminum foam on multi-cell plates. The findings revealed three failure modes and three stages of the impact force time history curve. Multi-cell plate exhibited showed much better specific energy absorption compared with the single-cell plate. Taking an example displacement of 22.5 mm, which differentiates the specific energy absorption the most between the two types of structures, the multi-cell plate exhibited an average increase of 332% in specific energy absorption compared to the single-cell plate. The numerical simulations were consistent with experimental results and highlighted the contribution of different components to energy dissipation in both structures.

Forming of Multiple Straight Convex Shapes on Aluminum Sheet Using Impulsive Water Pressure

Several types of multiple straight convex shapes were formed on a thin aluminum sheet with a grooved die using impulsive water pressure. The maximum pressure was 160 MPa in the high-speed forming, wherein a drop hammer testing machine was used, whereas it was 100 MPa in the low-speed forming because of the limitations of the press machine. The effects of the forming speed, cross-sectional shape, and pitch of the grooves on the deformation behavior were investigated. The increase in the impulsive water pressure was found to be affected significantly by the compressibility of water. The symmetricity of the convex shape in the cross-section decreased at both ends for a smaller pitch because of the imbalance of the material flow at both peripheries of the groove. The concave surface profile of the pressure side was more rounded in the high-speed forming than that in the low-speed forming when semicircular and rectangular grooved dies were used. This may be attributed to the fact that the plastic deformation becomes more uniform owing to the positive strain rate sensitivity of the test material. In the forming with rectangular grooves, fracture occurred under the low- and high-speed conditions, wherein the maximum pressure was set to 100 MPa. However, the material did not fracture during high-speed forming with a pressure of 160 MPa, where the convex shape was higher and the material contacted the bottom of the groove. This behavior may be because the dislocation density of the material did not increase rapidly owing to the strain rate being maintained high until the material suddenly stopped deforming in the latter condition. In forming with a trapezoidal grooved die, the formed profiles were considerably similar under all conditions because the strain was considerably smaller than that with the other grooves.

Dynamic analysis of hybrid basalt and carbon fiber reinforced Bismaleimide composites suited for high temperature structural applications

The main aim of this work is to study thedamage tolerance of hybrid basalt and carbon fiber-reinforced composite subjected to low velocity impact (LVI) at different velocities, 2.89 m s−1 and 4.42 m s−1, simulated using a CEAST drop hammer testing machine and Dynamic Mechanical Analysis(DMA) were conducted to characterize the sample. In this article, the detailed failure mechanism of seven composite laminates (Basalt fiber/Bismaleimide(BMI)-diallyl Bisphenol A(DABA), Carbon fiber/BMI-DABA, Carbon and basalt fiber(hybrid fibers)/BMI-DABA) were studied under loading of LVI. Through the experiment, it was also substantiated that the hybrid fiber-reinforced composites possessed better damage tolerance and thermo mechanical properties than the homogenous fiber-reinforced composites. The hybrid fiber composites that were produced vary in the number of carbon fiber to basalt fiber ratio and stacking sequence. The impacted surface was analyzed at macro level by using Image J software. The impact force, the energy absorbed, and the deformation of the laminates under impact load were scrutinized extensively, and it was inferred that the basalt fiber intercalated with carbon fiber with BMI/DABA possessed the highest damage resistance than the other composite laminates under study. The highest peak force 5702 N and 9241 N with the highest elastic energy 4.8 J, 11.7 J and with lower deformation (3.85 mm, 6.09 mm) and deformation area (22.79 mm2, 28.09 mm2) was observed in the intercalated hybrid laminate.

Research on fracture behavior of lightly reinforced concrete beam under different loading rates

Under impact loads, the crack resistance of reinforcement in concrete is the focus of impact dynamics research. In this study, the three-point bending tests of lightly reinforce concrete beams with notch were conducted with a drop hammer testing machine. The high speed camera and Digital Image Correlation (DIC) technology were applied to catch the fracture process and analyse the displacement field. The shape and geometry of specimen followed the RILEM recommendation, i.e., 150 mm × 150 mm in cross section, 800 mm in length, notch-depth ratio was around 1/3 and span was kept constant 600 mm. And the impact force, mid-span deflection, steel strain beneath the loading point and concrete strain at the notch tip were measured over four loading rates. The experiment results showed that the crack initiation strain rate increased linearlywith the loading rate, and the growth trend weakened when loading rate was 1.771×103 mm/s. Based on the test results, the empirical formula of crack initiation strain rate with respect to loading rate wasgiven, which was meaningful to simulate the crack initiation in concrete under dynamic loading. In addition, with the increase of loading rate, the steel yielded gradually, which resulted in the response time difference between impact force and steel strain decreased. With the recovery of elastic deformation of steel bars, the crack started to close and the macro crack became visible clearly. Meanwhile, the crack mouth opening displacement (CMOD) declined to a constant value after reaching the maximum value. Then, the crack mouth opening displacement rate was obtained from the fitting curve, and a linear growth relationship between CMOD rate and loading rate was founded. The failure process of the lightly reinforced beams was analyzed based on the CMOD rate, which provided an idea for comparing the fracture process of the beam under dynamic and static loads.

쉬트와 와이어 형태를 가진 형상기억합금 강화 케블라 고분자 복합체와 일반 케블라 고분자 복합체의 비교 연구

The main objective of this work is to investigate the effect of shape memory alloy reinforcement in Kevlar polymer composites on mechanical and low-velocity impact properties. The sheet and wire forms of shape memory alloy (SMA-nickel-titanium alloy) are used as potential reinforcements in Kevlar-reinforced polymer composite. The developed composites were analyzed for tensile and flexural behavior. The effective bonding area, referred to as core density, contributes to incremental flexural strength in the SMA sheet reinforced composites. The developed composites exhibited better impact resistance during low-velocity impact tests at different velocities, 2.80, 3.96, and 4.85 m/sec, and simulated using a CEAST drop hammer testing machine. The impact surface of the specimen was studied on a micro-level using SEM analysis and macro-level using Image J software. The impact force, the energy absorbed, and the deformation of the specimen during impact were recorded and analyzed. The experimental results reveal that the SMA sheet reinforced Kevlar composites exhibited appreciable impact resistance with maximum energy absorbing capacity comparatively with plain Kevlar and SMA wire reinforced composites.

Experimental Investigation of Mechanical and Dynamic Impact Properties of High Strength Cementitious Composite Containing Micro Steel and PP Fibers

Cementitious composites are one of the most consumed construction materials in the world. The use of cementitious composites is increasing due to their special characteristics. The behavior of high strength cementitious composites is improved by increasing the fiber percentage. In the present paper, the effects of steel microfibers and polypropylene fibers on mechanical properties and impact resistance of high strength cementitious composites are investigated. The percentage of fibers used in the study was 0, 0.5, and 1.5% in seven separate and three combined mix designs. Experiments were carried out on 120 specimens in 10 mix designs. Compressive strength, tensile strength, flexural strength, and dynamic impact tests were carried out on 10 mix designs manufactured in this research. The dynamic impact strength of the disc specimen was investigated by a drop hammer test machine with a capacity of 7500J. After testing the samples, it was shown that using a high percentage of steel and polypropylene fibers reduces the compressive strength and increases tensile strength, flexural strength, and impact strength. The effects of steel microfibers on the reduction of the crush displacement resulting from the dynamic impact were higher than that of polypropylene fibers.

Experimental investigation of impact loading effects on rectangular flat panels of fiber self-compacting cementations composite with expanded steel sheet

Impact loadings essentially differ from static loadings due to a huge amount of the force applied to milliseconds under these loadings. Energy absorption of composites is proper criteria to examine the function against impact loading. Energy absorbers are widely used in the industry. At the same time, due to their unique properties, the use of strong self-compacting composites has been considered by the researchers. High tensile, compressive, and flexural strengths have made these concrete composites more eminent. In a comprehensive experimental work, using four basic mix designs, 64 rectangular composite panels were made with 100 mm2 of area and 30, 45, 60, and 75 mm thickness and tested by impact loading. Compressive, tensile, and flexural strength tests were performed on all the four max designs. Steel fibers with percentages of 0, 0.25, 0.5, and 0.75 with 25 m of length were used to make the concrete composites. A hammer with 180 kg weight and 7500 J power was used as the impact loading with drop hammer test machine (DH-TM). The specimens were dynamically loaded by drop test from a 60 cm height. The use of steel fibers and expanded sheets in combination with each other significantly increases the energy absorption. Moreover, the initial peak force increases, while crushing length and deformation of the specimens reduce.

Low-velocity impact behavior of composites reinforced with weft-knitted spacer glass fabrics

Structural parameters of fabrics influence the mechanical behaviour of fabric-reinforced composites. Weft-knitted spacer fabrics have high energy absorption capacity. In this paper, low-velocity impact behavior of composites reinforced with weft-knitted spacer fabrics has been studied using energy-balance method. The effect of fabric geometry on the impact behavior of composites was investigated. A theoretical model was generated to predict the energy dissipated through the impact, considering the structural parameters of fabrics as reinforcement of composites. For this purpose, dissipated energies due to contact, membrane and bending deformation of fabrics, and buckling deformation of spacer yarns were considered. In order to evaluate the proposed model, weft-knitted spacer fabrics with two types of spacer yarn's orientation were used as reinforcement of composites. Low-velocity impact examinations were performed using the drop hammer testing machine. The results showed that the model has about 12 and 13% error in prediction of dissipated energies of different samples. Comparison between theoretical and experimental results confirms that the proposed model is capable to predict the impact behavior of weft-knitted spacer fabric-reinforced composites.

Experimental study on dynamic split tensile properties of rubber concrete

Static and dynamic split tensile tests were conducted on rubber concrete with varied volume fractions of rubber particles that replaced fine aggregate (10%, 20%, 30%, 40%, and 50%, named as RC10, RC20, RC30, RC40, and RC50, respectively). The flattened Brazilian disc specimens were applied to determine the tensile properties and energy absorption capabilities under high strain rate by an SHPB (Split Hopkinson Pressure Bar) and medium strain rate by a drop-hammer testing machine. With a high-speed camera, the crack growth of specimens in the SHPB and drop-hammer impacting tests was observed and validated. The experimental result of five rubber concretes and one normal concrete without rubber particles was obtained, and the strain-rate effect on tensile strength of rubber concretes and normal concrete was confirmed. For high strain rate, RC10, RC20 and RC30 were sensitive to strain rate dependence, but rate dependence of RC40 and RC50 was lower than normal concrete. RC30 exhibited the most sensitivity and excellent energy absorption capability in static and dynamic tests. Excessive rubber content did not continually increase the toughness of the concrete under dynamic loadings.

Analytical, numerical and experimental investigation of low velocity impact response of laminated composite sandwich plates using extended high order sandwich panel theory

The Nonlinear dynamic response of a sandwich plate subjected to the low velocity impact is theoretically and experimentally investigated. The Hertz law between the impactor and the plate is taken into account. Using the Extended High Order Sandwich Panel Theory (EHSAPT) and the Ritz energy method, the governing equations are derived. The skins follow the Third order shear deformation theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the three dimensional elasticity is used for the core. The nonlinear Von Karman relations for strains of skins and the core are adopted. Time domain solution of such equations is extracted by means of the well-known fourth-order Runge-Kutta method. The effects of core-to-skin thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that these parameters play significant role in the impact force and dynamic response of the sandwich plate. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The results are compared with experimental data acquired by impact testing on sandwich plates as well as the results of finite element simulation.

Geometrically nonlinear analysis of sandwich beams under low velocity impact: analytical and experimental investigation

Nonlinear low velocity impact response of sandwich beam with laminated composite face sheets and soft core is studied based on Extended High Order Sandwich Panel Theory (EHSAPT). The face sheets follow the Third order shear deformation beam theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the two dimensional elasticity is used for the core. The nonlinear Von Karman type relations for strains of face sheets and the core are adopted. Contact force between the impactor and the beam is obtained using the modified Hertz law. The field equations are derived via the Ritz based applied to the total energy of the system. The solution is obtained in the time domain by implementing the well-known Runge-Kutta method. The effects of boundary conditions, core-to-face sheet thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that each of these parameters have significant effect on the impact characteristics which should be considered. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The contact force histories predicted by EHSAPT are in good agreement with that obtained by experimental results.

Dynamic Behaviour and Catenary Action of Axially-restrained Steel Beam Under Impact Loading

In this paper, the dynamic response and catenary action of axially restrained steel beam under impact loadings is examined through a combination of experimental and numerical investigations. The results of six impact tests on the axially restrained welded H-beams by means of the drop hammer test machine are presented. The main behavioural patterns and the key response characteristics including the development of impact force, deformation and strain, as well as failure modes are examined, with emphasis on the effect of impact energy and the width to thickness ratio of beam flange. Finite element models are also developed and validated against the available testing results. It is demonstrated that the detailed FE model can reasonably capture the response of the welded H-beams under impact loadings. Moreover, the mechanism of catenary action was identified based on the development of the internal force in the welded H-beams.

Deformation behavior of axially compressed aluminum polygonal tube

Abstract Aluminum tubes are efficient energy absorbing components and are widely used as framework and reinforcement members of structures. This paper deals with the influence of the axial length, cross-sectional shape and reinforcing rib on a dynamic axially compressed aluminum polygonal tube in order to obtain basic data on buckling. The axial impact test of an aluminum square tube was carried out with a drop-hammer testing machine. The dynamic deformation process of a polygonal tube was analyzed by a finite element method. The specimen used in this analysis is an aluminum polygonal tube (square, hexagonal, octagonal and decagonal). The result shows that even when the axial length was changed, there was no difference in the trend of the compressive load-time curve in each cross-sectional shape. The trend of the compressive load-time curve was affected by the reinforcing ribs. The buckling was generated partially in each axial length and cross-sectional shape. In the case of a square tube without ribs, the deformation shape was concave-convex in adjoining surfaces, and crushed in a bellows-like manner. As for the deformation shape, the experimental results approximately agreed with those of the finite element method analysis.

Proactive regulation of axial crushing behavior of thin-walled circular tube by gradient grooves

The progressive buckling behavior of a gradient grooved tube (GGT) designed for high temperature gas cooled reactor (HTR) is systematically studied in this paper. Based on the plastic hinge formation process, a sectionalized theoretical model is established to predict the quadratic upward trend of crushing force of GGT. The ordered and stable energy absorbing process of GGT is examined by low-speed axial impact using drop hammer test machine. The effect of proactive regulation parameters, including non-dimensional groove width W/(h0+h), groove depth h0/h and half wavelength (H+W−h)/Dh on buckling modes and force–displacement curve is determined by experiments and FE simulation. The non-dimensional groove width W/(h+h0) is determined as π/2 according to the geometry coordination of bending grooves. The non-dimensional groove depth h0/h influences local buckling behavior and the critical value 0.6 for regular bending has been determined by numerical simulation. The quadratic trend force–displacement curves of GGT can be actively controlled by (H+W−h)/Dh within a certain range less than 1.2. Free-fall impact experiments show that GGT has a better stability than perfect tube when used as an energy absorber to protect the graphite in HTR from slender control rod impact.

Research on the energy absorption properties of aluminum foam composite panels with enhanced ribs subjected to uniform distributed loading

A new design of aluminum foam composite panels with enhanced ribs was proposed, and the energy absorption property of it was analyzed by combining dynamic testing and numerical simulation. The optimization of aluminum foam composite panels with enhanced ribs was investigated assuming that the panels had the same total mass. An Instron drop hammer test machine was used to study the dynamic compressive behavior of the new composite panels and the impact deformation characteristics of the components. Finite element method (FEM) software was employed to simulate the loading process, and the simulation results were compared with the experimental data for validating the reliability of the model. The effect of rib-mass ratio on the energy absorption property was investigated, and the energy absorption capacities of the new composite panels and conventional sandwiches were compared at different impact velocities. The analysis shows that, compared with conventional sandwich panels, aluminum foam composite panels with enhanced ribs have better energy absorption subjected to uniform distributed loading; and both rib-mass ratio and impact velocity have an effect on the normalized energy absorption. The results of this study can be a reference for related academic research and engineering application.

An Investigation on Low Velocity Impact Response of Multilayer Sandwich Composite Structures

The effects of adding an extra layer within a sandwich panel and two different core types in top and bottom cores on low velocity impact loadings are studied experimentally in this paper. The panel includes polymer composite laminated sheets for faces and the internal laminated sheet called extra layer sheet, and two types of crushable foams are selected as the core material. Low velocity impact tests were carried out by drop hammer testing machine to the clamped multilayer sandwich panels with expanded polypropylene (EPP) and polyurethane rigid (PUR) in the top and bottom cores. Local displacement of the top core, contact force and deflection of the sandwich panel were obtained for different locations of the internal sheet; meanwhile the EPP and PUR were used in the top and bottom cores alternatively. It was found that the core material type has made significant role in improving the sandwich panel's behavior compared with the effect of extra layer location.