Split Hopkinson Pressure Bar Method Research Articles

Strain rate dependence of anisotropic compression behavior in porous iron with unidirectional pores

The strain rate dependence of anisotropic compression behavior in porous iron with cylindrical pores oriented in one direction was investigated. Through high strain rate (˜103 s−1) compression tests along the orientation direction of pores using the split Hopkinson pressure bar method, it was shown that the stress–strain curve exhibits a unique plateau-stress region where deformation proceeds with almost no stress increase. The appearance of the plateau-stress region is related to the buckling deformation of the iron matrix and provides superior energy absorption. However, for the middle (˜10−1 s−1) and low strain rates (˜10−4 s−1), compression along the same direction produces no such plateau region. In fact, in contrast to compression in the parallel direction, compression perpendicular to the orientation direction of pores produces no plateau-stress regions in any of the three strain rates.

Obtaining Constitutive Relationship for Rate-Dependent Rock in SHPB Tests

A large number of tests have recently been conducted with the Split Hopkinson pressure bar (SHPB) method to determine the characteristics of rock dynamics. However, it is still impossible to get test results at a perfect constant strain rate from this set-up owing to the rate dependency of rock materials. For instance in most cases, dynamic behavior of rock can only be described with an average strain rate. The results from these methods, including rich strain rate information, frequently tend to be inexplicable or self-contradictory. The obtained stress–strain curves can then never be directly treated as constitutive curves as in static tests. In this paper, the reasons behind the controversial stress–strain results with current methods are analyzed. In addition, the requirement for the rock specimen to deform at a constant strain rate is demonstrated after theoretical analysis of correlations among specimen, deforming stress, incident stress, reflected stress and transmitted stress. With test results from SHPB by pulse shaper and special shape striker methods, the requirement is verified. Finally, the method of 3D scattergram considering stress–strain–strain rate simultaneously is brought up to get constitutive relationships of rate-dependent rock. The new method gives reasonable predictions for constitutive relationships of rock at different strain rates. At the same time, the new method has fewer requirements and has a wider application scope for SHPB tests.

Finite-element analysis of SHPB tests on double-lap adhesive joints

Adhesively bonded assemblies are in increasing use in multiple engineering applications. However, they can endure impact loads. The measurement, of these assemblies mechanical behaviour, under dynamic loads is of great concern. Several works used the split Hopkinson pressure bar (SHPB) method to assess the strength of adhesive joints at high loading rates. In this paper, we investigated the accuracy of SHPB tests on double-lap bonded joints by three-dimensional finite-element analysis. For this analysis, an elastic behaviour is assumed for both adherends and adhesive. We were interested in the influence of material, geometrical and dynamic parameters on the SHPB accuracy. From this study, we can conclude that the SHPB bar method gives a good estimation of the mean adhesive stress value. However, its estimation, to the mean adhesive strain and to the maximum adhesive stress and strain, is rather bad. A unified parameter is therefore proposed to help designing specimens and to correct the SHPB results.

Study of adiabatic localized shear in metals by split Hopkinson pressure bar method

This paper is devoted to the technique for study of localized shear using hat-shaped samples by the split Hopkinson pressure bar (SHPB) method. Also it is devoted to results obtained in tests with samples of copper M1 and steel 09G2S. The tests were performed using hat-shaped samples with beforehand-determined direction of forced shear. Sizes of samples were thoroughly selected in order to minimize plastic deformation of the hat-shaped part and the ring base, which are in contact with the bar ends. Results of testing of copper M1 and steel 09G2S were obtained; “shear stress-displacement” diagrams were plotted. Values of amplitudes and durations of loading pulses were determined. Also shear stresses were determined when adiabatic localized shear was formed in case of this geometry of samples.

610 ひずみ速度がデンプン由来生分解性プラスチックの降伏応力に与える影響(材料・構造部材の動的特性(1),ものづくりにおける基礎研究と先端技術の融合)

The dynamic compressive properties of starch-based biodegradable plastics were measured over a wide range of strain rates from 10^<-4> to 10^<-3> s^<-1> by using a split Hopkinson pressure bar method. In addition, compressive and tensile static stress-strain curves of starch-based biodegradable plastics were measured at a strain rate of 10^<-3> s^<-1>. We determined constants of Drucker-Prager yield criterion for starch-based biodegradable plastics, and drew the yield curves in the second deviatoric stress and invariant-first invariant of stress. The compressive yield stress is dependent upon the strain rate.

A Polymeric Split Hopkinson Pressure Bar Method and Its Applications to Low Impedance Materials

A Polymeric Split Hopkinson Pressure Bar Method and Its Applications to Low Impedance Materials

1211 植物由来エンプラ・ポリアミド11の衝撃特性の評価(OS12-4 実験・計測における先端技術とその応用-材料特性評価-)

The effects of strain rate, water absorption and specimen's temperature on impact properties of a plant-derived engineering plastic, polyarnide 11, were examined. Stress-strain curves of the polyamide 11 were measured over a wide range of strain rates from 10^<-4> s^<-1> to 10^3 s^<-1>, using a quasi-static compression testing machine and a split Hopkinson pressure bar (SHPB) method. The strain rate slightly affected Young's modulus and considerably increased flow stress. In addition, the effect of water absorption and specimen's temperature from 5℃ to 65℃ on flow stress was also examined. Flow stress decreased with water absorption and increasing specimen's temperature.

S0404-1-4 環境水素の影響を受けた6061および7075アルミニウム合金の衝撃引張特性(衝撃問題の新たなる展開と応用(1))

Impact tensile properties of T6-aged 6061 and 7075 aluminum alloys affected by atmospheric hydrogen were investigated. In order to introduce hydrogen from the atmosphere, the alloys were pre-deformed by a slow strain rate testing in a humid air atmosphere with a relative humidity of 90 %. For the pre-deformed specimens, the impact tensile tests were performed using split Hopkinson pressure bar method at an average strain rate of 5.0×10^2s^<-1> a set of the experiments, it was shown that the ductility in the impact test decreased when the T6-aged 7075 alloys were hydrogen charged. The hydrogen embrittlement sensitivity of the T6-aged 6061 alloys was lower than that of the T6-aged 7075 alloys. The decrease of the ductility due to hydrogen charging of the T6-aged 7075 alloys was closely related to the increase in the ratio of the intergranular fracture near the specimen surface.

数値シミュレーションによるTRIP鋼の衝撃変形挙動の評価

Due to a strain-induced martensitic transformation (SIMT), a strength, a ductility and a toughness of the TRIP steel are enhanced. Recently, a low-alloyed high strength steel based on the TRIP steel is under development and its application to an impact absorption member is being investigated. Therefore, an evaluation of an energy absorption characteristic of the TRIP steels is quite essential. An experimental approach provides us the SIMT behavior under only static deformation since it is difficult to capture a moment of the phase evolution and temperature rise for the impact deformation. Thus, a computational approach with an appropriate constitutive model for TRIP steel can be powerful for its evaluation. Here, the impact compressive deformation behavior of TRIP steel is experimentally studied by the split Hopkinson pressure bar (SHPB) method at room temperature. Then, a finite element equation with the constitutive model for the TRIP steel proposed in the past is derived from a rate form of the principle of virtual work based on an implicit time integration scheme. After the results between the computation and the experiment for an impact compression are compared to confirm an validity of the computation, an impact deformation behavior under tensile deformation at a various temperature are evaluated.

Effects of the Strain Rate and Alloying on the Compression Characteristics of Closed Cell Aluminum Foams

Though closed cell Al foams have extremely low density and high energy absorption performance, they are expected to improve the compressive strength and to clear the dynamic compression characteristics for much more practical application. In this research, the effects of density, test piece size and alloying (Al-10.0 mass%Zn-0.3 mass%Mg) on the uniaxial static and dynamic compressive strength was examined. Dynamic compressive strength were examined by the Split Hopkinson Pressure Bar (SHPB) method and the drop weight impact test device. As a result, the dynamic plateau stress of pure Al foams was about 1.3 times larger than the static one, and there was a scale effect of test pieces. The dynamic plateau stress of Al alloy foams was about 1.1 times larger than the static one, and there was less scale effect of test pieces for plateau stress because the cell walls of Al alloy foams tend to collapse owing to brittleness by alloying. The effect of the inner gas enclosed in cells on the dynamic response of pure Al foams by SHPB is also discussed. When providing inner gas vent holes, dynamic plateau stress decreased close to the static one. With Al foams, the increasing in dynamic plateau stress may be caused by the inner gas pressure rising under dynamic compressive conditions as well as influence of the strength and ductility of the cell wall. [doi:10.2320/matertrans.MRA2008487]

A STUDY ON IMPACT DEFORMATION AND TRANSFORMATION BEHAVIOR OF TRIP STEEL BY FINITE ELEMENT SIMULATION AND EXPERIMENT

Due to strain-induced martensitic transformation (SIMT), the strength, ductility and toughness of TRIP steel are enhanced. The impact deformation behavior of TRIP steel is very important because it is investigated to apply it for the shock absorption member in automobile industries. However, its behavior is still unclear since it is quite difficult to capture the transformation behavior inside the materials. There are some opinions that the deformation characteristics are not mainly depending on the martensitic transformation due to heat generation by plastic work. Here, the impact compressive deformation behavior of TRIP steel is experimentally studied by Split Hopkinson Pressure Bar (SHPB) method at room temperature. In order to catch SIMT behavior during impact deformation, volume resistivity is measured and a transient temperature is captured by using a quite thin thermocouple. Then, a finite element simulation with the constitutive model for TRIP steel is performed. The finite element equation can be derived from the rate form of principle of virtual work based on the implicit time integration scheme. Finally, the results between the computation and experiment are compared to confirm the validity of computational model.

STRAIN RATE EFFECTS ON COMPRESSIVE PROPERTIES OF A BIODEGRADABLE PLASTIC

The compressive properties of a biodegradable plastic were measured over a wide range of strain rates from 10−5 to 104 s −1, using a universal testing machine and a split Hopkinson pressure bar method. The yield stress of the biodegradable plastic increased with increasing strain rate and decreased with temperature and water absorption. Empirical equations for the yield stresses were derived for the strain rates from 10−5 to 103 s −1 and from 103 to 104 s −1, respectively.

IMPACT TENSILE PROPERTIES IN AL-MG-SI BASE ALLOYS FOR AUTOMOTIVE USE

Effect of alloy composition on impact tensile properties [Formula: see text] in Al - Mg - Si base alloys was investigated by means of the split Hopkinson pressure bar method. As a result of the impact test, it was proved that the nominal stress for 5% plastic strain was not changed by changing the strain rate regardless of the alloy composition. In the impact test, the elongation was decreased with increasing the amount of excess Si , while that was increased by the addition of Cu . Fractography revealed that the reduction of the elongation in the excess Si alloy was caused by the change of the fracture mode from the mixture of transgranular and intergranular fracture to the intergranular fracture.

INTEGRATED STUDY OF DYNAMICAL PROPERTIES OF AK4-1 ALUMINUM ALLOY

Results of experimental studies and numerical modeling of high strain rate of aluminum alloy AK4-1 (analog AU2GN) have been presented. Using Split Hopkinson Pressure Bar (SHPB) method stress-strain curves under compression and tension have been obtained. On the basement of these results appropriate parameters of some constitutive equations have been calculated. Strength and deformation material failure properties, dynamic crack resistance, dynamic friction factor for material pair aluminum-titanium have been obtained by carrying out of modificated SHPB tests. A verification of the constitutive equations has been realized by dynamic indentation method and modified Taylor test.

OS0914 分割式ホプキンソン棒法を用いた幾つかの構造用接着剤の衝撃変形挙動及びひずみ速度依存性に関する研究(OS09-04 材料・構造の衝撃問題4,OS09材料・構造の衝撃問題(2))

本研究では代表的な衝撃試験法である分割式ホプキンソン棒法を用いて、構造用接着剤の衝撃変形挙動及びひずみ速度依存性を調査する.構造用接着剤の低機械的インピーダンスを考慮して、入力棒左端面に純銅製の薄円盤を貼り付けることにより、入射応力波を制御する.また、構造用接着剤の塑性変形を表す単軸構成式の定式化を試み、実験結果とモデルの比較検討を行う.塑性変形領域及びひずみ軟化領域を除き簡易的に塑性流動性の定式化が可能となった.

1545 でんぷん系生分解性プラスチックの動的圧縮特性に与える温度の影響(S11-4 バイオマス由来材料の成形加工と特性評価(4)生分解性プラスチックの成形性と機械的性質,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The effect of strain rate and temperature on compressive properties of starch-based biodegradable plastics (Nihon Cornstarch Co., CPR-M2) was examined. Dynamic stress-strain curves of starch-based biodegradable plastics were measured over a wide range of strain rates from 10^<-5> s^<-1> to 10^4 s^<-1>, using a quasi-static compression testing machine and a split Hopkinson pressure bar (SHPB) method. A master curve of 7% flow stress, reduced to 297 K, was made. The values of activation energies related to the α and β relaxation processes were respectively estimated from the master curve of 7 % flow stress and from the best fit of equations based on Ree-Eyring theory and Bauwens' treatment.

Low frequency limitations of the split Hopkinson pressure bar method for identification of complex modulus

Low frequency limitations of a recently developed method for identification of complex modulus utilizing the split Hopkinson pressure bar (SHPB) technique were investigated using computer simulations. Specifically, the effects of truncation, noise and discretization were examined. It was shown that the low frequency limitation of the method generally corresponds to the inverse of the length of the time signal. Further, it was shown that all three factors have an effect on the low frequency accuracy of the method and that careful consideration of these factors is necessary to optimize the capability of the method. Finally, it was shown how averaging techniques can be implemented to reduce the undesirable effects of truncation and noise.

Mechanical properties of bovine cortical bone at high strain rate

Intense investigation has been performed to characterize static and dynamic mechanical properties of trabecular and cortical bone. The Split Hopkinson Pressure Bar (SHPB) technique has been applied with success in the study of mainly other engineering materials, and constitutive laws concerning the dynamical behaviour of these have been derived. This paper describes the characterization of mechanical properties of fresh bovine cortical bone at different high strain rate using the SHPB method. Cube specimens of dimensions 10 × 10 × 10 mm of bone were prepared according to longitudinal and transverse directions. The differences of results for ultimate strength (max. 281 MPa; min. 240 MPa), strain at fracture (max. 45.3 mm/m; min. 32.6 mm/m) and elastic modulus (max. 9.9 GPa; min. 6.8 GPa) in these directions were not statistically significant. Overall, for both longitudinal and transverse directions the elastic modulus decreased and the ultimate strength increased for higher strain rates.

Accuracy of Viscoelastic Split Hopkinson Pressure Bar Method Using PMMA Bars

Accuracy of Viscoelastic Split Hopkinson Pressure Bar Method Using PMMA Bars

328 輪転印刷機におけるブランケットの動的特性(材料の動的特性)

The rotary printing machine requires preventing vibration because the vibration causes printing degradation. The blanket used in the rotary printing machine consists of rubber, sponge and fabric. We investigated dynamic characteristic of the blanket for curbing vibration. Therefore, we conducted dynamic compression impact test by SHPB (split Hopkinson's pressure bar) method and DMA (Dynamic Mechanical analysis). The result showed that elastic modulus of the blanket depended on the strain-rate and frequency.