Split Hopkinson Pressure Bar Method Research Articles

Effect of Foam Structure on Impact Compressive Properties in Foamed Polyethylene Film

The purpose of this study is to elucidate the effect of foam structure on the impact compressive properties of foamed polyethylene film. Three types of foamed PE film were prepared, which have different foam structure: base type, spheral type and dense type. A quasi-static test was performed using a universal testing machine at the strain rate of 10-3~10-1s-1. Impact tests were carried out using a drop-weight testing machine at the strain rate of 101~102s-1 and using a split Hopkinson pressure bar method at the strain rate of approximately 103s-1. It was confirmed that the foamed PE film shows an increase of the flow stress with increasing of the strain rate, regardless of the specimen type. In the spheral type specimen, the elastic response is observed immediately after compression because the cell shape of this specimen has high bending resistance in comparison with the other two specimens. In addition, it is confirmed that the relative density and cell size affects the flow stress in the foamed PE film.

Effect of Ductile Agents on the Dynamic Behavior of SiC3D Network Composites

Co-continuous SiC ceramic composites using pure aluminum, epoxy, and polyurethane (PU) as ductile agents were developed. The dynamic mechanical behavior and failure mechanisms were investigated experimentally using the split Hopkinson pressure bar (SHPB) method and computationally by finite element (FE) simulations. The results show that the SiC3D/Al composite has the best overall performance in comparison with SiC3D/epoxy and SiC3D/PU composites. FE simulations are generally consistent with experimental data. These simulations provide valuable help in predicting mechanical strength and in interpreting the experimental results and failure mechanisms. They may be combined with micrographs for fracture characterizations of the composites. We found that interactions between the SiC phase and ductile agents under dynamic compression in the SHPB method are complex, and that interfacial condition is an important parameter that determines the mechanical response of SiC3D composites with a characteristic interlocking structure during dynamic compression. However, the effect of the mechanical properties of ductile agents on dynamic behavior of the composites is a second consideration in the production of the composites.

Anisotropic dynamic mechanical response of tungsten fiber/Zr-based bulk metallic glass composites

The anisotropic dynamic mechanical behavior of the W fiber/Zr-based bulk metallic glass composites (Wf/BMGCs) with different W fiber orientations (θf) were investigated by split Hopkinson pressure bar (SHPB) and finite element method (FEM). The composites exhibited the most excellent mechanical properties at θf of 0° while the poorest at θf of 45°. The composites failed by longitudinal splitting at θf of 0°, shearing at θf of 45°, a mixture of shearing and splitting during 0°<θf<45° or 45°<θf<90°, and a mixture of shearing and transverse splitting at θf of 90°. Strain rate sensitivity of the composites also varied with θf, exhibiting positive strain rate sensitivity at θf of 0°, 15°, 60°, and 75° ranging from the strain rate of 10−3 to 2.1×103s−1, positive strain rate sensitivity with the strain rate ranging from 10−3 to 10−2s−1 but negative strain rate sensitivity from 10−2 to 2.1×103s−1 at θf of 30° and 90°, and even strain rate insensitivity at θf of 45°.

射出成形ガラス長繊維強化ポリアミドの衝撃引張特性に及ぼす繊維径の影響

Applications of fiber reinforced plastics have been expanding due to improvement of not only fuel efficiency but also the motion performance of some recent vehicles. Especially, the demand for injection-molded fiber reinforced thermoplastics is expected to increase because of their superior moldability, productivity and recyclability. In this study, the influence the fiber diameter has on the impact tensile properties of long glass-fiber reinforced polyamide (GF/PA) is investigated using the split Hopkinson pressure bar method. Prior to the tensile tests, an investigation of the fiber-orientation distribution was conducted in order to cut out specimens with the same fiber orientation angle from the injection molded plate. Two types of specimens, referred to as specimens with high- and low orientation angle, were manufactured using glass fibers with average diameters of 13, 17, 23 μm. In the tensile test, the GF/PA with smallest fiber diameter showed the highest tensile strength and the most significant strain rate dependency on the strength. These effects were more significant for the specimens with high orientation angle. From SEM observations on the fracture surface and an average fiber length measurement, it was observed that the interfacial fracture and the fiber breakage were dominant failure modes under the considered tensile loading conditions. It was suggested that decreasing the stress acting on the fiber/matrix interface by reducing the fiber diameter affected the improvement of the GF/PA strength. Using the modified linear rule of mixtures, the tensile strength was predicted. The predictions showed good agreement with experimental results. Therefore, it is believed that the decrease of critical fiber length is the reason that the impact tensile properties are higher for the samples with smaller fiber diameter.

ホプキンソン棒法によるラミー繊維/ＰＬＡ/PBAT複合材の引張特性の評価

In order to improve the tensile properties, natural fiber was added to PLA/PBAT/PEEHEXA polymer alloy. We have done researches on effects of chemical treatment to the fiber and physical treatment to the polymer alloy ,the mixing ratio of PLA/PBAT as well. Also the tensile properties of specimens were measured using split Hopkinson pressure bar method at high strain rates.

FCC系高エントロピー合金の衝撃変形挙動と組織変化

In recent years, new solid solution alloy called High Entropy Alloy (HEA) has been attracting attention. CoCrMnNiFe equiatomic alloy is expected as a new structural material because of its excellent mechanical property. However understanding of the deformation mechanismin the CoCrMnNiFe alloy is still not sufficient. In this study, CoCrMnNiFe alloy was loaded at room temperature quasi-statically or dynamically by Split-Hopkinson Pressure Bar (SHPB) method at the strain rate of 103 s-1. CoCrMnNiFe alloy showed higher yield stress under the dynamic loading than that at the quasi-static rate. Therefore, it is suggested that this alloy possesses the strain rate dependence of the yield stress. Deformation twining was not observed in the dynamically deformed micro structure. It suggests that the dominant deformation mechanism of CoCrMnNiFe is dislocation slip

Effects of Silica Nanoparticle Addition on Dynamic Properties of Poly(lactic acid)

Bioplastics are plastics derived from renewable sources such as corn starch or microbe and biodegradable plastics are plastics that are capable of being decomposed by bacteria or other living organisms. Poly (lactic acid) (PLA) is a typical and biodegradable bioplastic. It has been recognized as a promising alternative material for petroleum-based polymers. In order to increase Young’s modulus, in the present study, silica nanoparticles were added to PLA. The effects of the addition of silica nanoparticles and the surface treatment of nanosilica particles on dynamic properties of nanoparticle added PLA were examined using tensile split Hopkinson pressure bar method and the Izod impact strength tests.

Effect of W volume fraction on dynamic mechanical behaviors of W fiber/Zr-based bulk metallic glass composites

The effect of W volume fraction (Vf) on dynamic mechanical behavior of W fiber/Zr-based bulk metallic glass composites (Wf/BMGCs) was investigated by split Hopkinson pressure bar (SHPB) and finite element method (FEM). The yield strength increased with the increase of Vf under both quasi-static and dynamic compression, and the dynamic flow stress is obviously greater than that under quasi-static compression. The fracture strain also increased with the increase of Vf under dynamic compression, which is different from that the composite with ~70vol% W exhibited the highest fracture strain under quasi-static compression. With the increase of Vf under both quasi-static and dynamic compression, the failure mode of the composites changed from shearing to a mixture of shearing and splitting, and lastly only splitting. High strain rate suppressed macro-shearing but promoted micro-shearing and splitting compared to that under low strain rate, which is suggested to be the reason why the composites exhibited different rules of strain rate-related fracture strain under quasi-static and dynamic compression.

Strain-rate sensitivity of aluminum 2024-T6/TiB2 composites and aluminum 2024-T6

Strain-rate sensitivities of 55vol%–65vol% aluminum 2024-T6/TiB2 composites and the corresponding aluminum 2024-T6 matrix were investigated using split Hopkinson pressure bar method. The experimental results showed that 55vol%–65vol% aluminum 2024-T6/TiB2 composites exhibited significant strain-rate sensitivities, which were three times higher than the strain-rate sensitivity of the aluminum 2024-T6 matrix. The strain-rate sensitivity of the aluminum 2024-T6 matrix composites rose obviously with increasing reinforcement content (up to 60%), which agreed with that from the previous researches. But it decreased as the ceramic reinforcement content reached 65%. After high strain rates compression, a large number of dislocations and micro-cracks were found inside the matrix and the TiB2 particles, respectively. These micro-cracks can accelerate the brittle fracture of the composites. The aluminum 2024-T6/TiB2 composites showed various fracture characteristics and shear instability was the predominant failure mechanism under dynamic loading.

Dynamic compressive properties of bovine knee layered tissue

In Japan, the most common articular disease is knee osteoarthritis. Among many treatment methodologies, tissue engineering and regenerative medicine have recently received a lot of attention. In this field, cells and scaffolds are important, both ex vivo and in vivo. From the viewpoint of effective treatment, in addition to histological features, the compatibility of mechanical properties is also important. In this study, the dynamic and static compressive properties of bovine articular cartilage-cancellous bone layered tissue were measured using a universal testing machine and a split Hopkinson pressure bar method. The compressive behaviors of bovine articular cartilage-cancellous bone layered tissue were examined. The effects of strain rate on the maximum stress and the slope of stress-strain curves of the bovine articular cartilage-cancellous bone layered tissue were discussed.

OS0705-278 牛の関節軟骨-海綿骨複層組織の圧縮特性に与えるひずみ速度の影響

The tissue engineering and regenerative medicine have received a lot of attention. In this field, cells and scaffolds are important both ex vivo as well as in vivo. From the view point of effective treatment, in addition to histological feature, the compatibility of mechanical properties is also important. In this study, the dynamic and static compressive properties of bovine articular cartilage-cancellous bone layered tissue were measured using a universal testing machine and a split Hopkinson pressure bar method.

Strain rate effects on tensile strength of iron green bodies

Impact tensile strength of iron green bodies with densities of 7.2 and 7.4 g/cm3 was examined by Brazilian test using the split-Hopkinson pressure bar (Kolsky bar) method. The powder material used for the experiments was a press-ready premix containing Distaloy AE, graphite, and lubricant. During dynamic compression, the failure behavior of specimens was observed using a high-speed video camera. The failure stress and failure behavior of dynamic compressive tests were compared with those of static compressive tests.

Development of experimental methods for impact testing by combining Hopkinson pressure bar with other techniques

The split Hopkinson pressure bar (SHPB) technique and the wave propagation inverse analysis (WPIA) technique are both extensively used to experimentally investigate the impact behavior of materials, although neither of them alone provides a fully satisfactory analysis. In the present paper, attention is given to new experimental techniques by incorporating a damage-modified constitutive model into the SHPB technique and combining the Hopkinson pressure bar (HPB) technique with WPIA. First, to distinguish the response due to dynamic constitutive behavior and the response due to dynamic damage evolution, the SHPB method incorporating a damage-modified constitutive model is developed, including an explicit damage-modified Zhu-Wang-Tang model and an implicit damage-modified constitutive model. Second, when the SHPB results become invalid, a method of combining new Lagrange inverse analyses with the HPB technique is developed, including cases of the HPB arranged in front of a long specimen and behind the specimen. As examples of these new methods, typical results are given for nonlinear viscoelastic polymers and concretes considering damage evolution, a super-elastic Ti-Ni alloy with phase transformation and an aluminum foam with shock waves propagating within it.

Quasi-static and high strain rates compressive response of iron and Invar matrix syntactic foams

Abstract The present work is focused on developing iron and FeNi36 Invar matrix syntactic foams and studying their properties under quasi-static and high strain rate compression. The quasi-static compression is conducted at a strain rate of 10−3 s−1. High strain rate testing is performed using a split-Hopkinson pressure bar (SHPB) at strain rates up to 2500 s−1. One of the limitations of the SHPB method is that it does not provide useful results at the intermediate strain rates where the specimens do not fail completely during the test. In the present study, a recently developed repeated testing scheme is applied to obtain results at such intermediate strain rates. Syntactic foams containing 5 and 10 wt.% hollow glass microballoons (GMBs) are synthesized using the metal powder injection molding (MIM) process for this study. The results show that the yield strength decreases with increasing GMB content. The quasi-static yield strengths of 5 and 10 wt.% GMB syntactic iron foams were found to be 14% and 17% lower than that of iron. Similarly, 5 and 10 wt.% GMB syntactic Invar foams had 35% and 51% lower yield strength than Invar alloy. However, weight-related strength was found to increase with GMB content and exceed the respective data of other iron and steel foams. High strain rate testing revealed a weak trend towards yield strength increase with strain rate. However, the indication of strain rate sensitivity is not very strong due to scatter in data. Metallographic analyses conducted on failed specimens showed that the extent of matrix plastic deformation decreased with increasing strain rate. Particle crushing was observed at all strain rates.

Tensile Properties of 7075 Aluminum Alloys Subjected to Pre-Fatigue in Humid Environment

The tensile properties of the quasi-static and the impact tests for 7075 aluminum alloys subjected to pre-fatigue deformation in a humid environment were investigated. An impact tensile test of the pre-fatigue deformed specimens was performed by means of the Split Hopkinson pressure bar method. Within the authors set of experiments, the flow stress in both the quasi-static and the impact tests was unaffected by the pre-fatigue deformation. On the other hand, it was shown that the ductility of the pre-fatigue specimen was slightly lower than that of the non-fatigue specimen. Additionally, the pre-fatigue specimen in a high-humidity environment had a lower ductility than in a low-humidity environment. The ductility of the quasi-static test was decreased as compared with the impact test. It is thought that the ductility loss occurred due to changes in the microstructure, such as dislocations caused by the presence of hydrogen in the specimen due to pre-fatigue deformation in a high-humidity environment.

A Study on Reduction of Friction in Impact Compressive Test Based on the Split Hopkinson Pressure Bar Method by Using a Hollow Specimen

The split Hopkinson pressure bar (SHPB) technique is widely-used to describe the impact compressive behavior of different materials including metals. During the impact test, the specimen deforms in a wide range of impact strain rate from 102 to 104 s-1. It is a reason why the method is studied for many years even though the structure of the apparatus based on the SHPB is simple. Actually, the cylindrical specimens are widely used for a compressive test and it is clearly seen that stress measured by the test includes the increment of stress (an error) derived by friction effect between a specimen and pressure bars. Therefore, it is important that the measured stress should indicate similar value as the proper stress of the material by reducing friction effect during not only quasi-static but also the impact test. Various attempts to reduce a friction effect in past have been conducted. A method to reduce friction effect is in general a use of lubricants. However, it is ineffective because it can be considered that this method contributes to an attenuation of the stress wave for obtaining the stress-strain curve under impact loading. Thus, rise time of waves obtained by the experiment becomes longer compared with a case not to use lubricants. Recently, a study can be found using a ring specimen, however, the determined thickness of the specimen is quite thin and it can be considered that a buckling effect cannot be vanished. In this study, a use of hollow specimen is suggested to solve the problem related to reduce the friction effect by decreasing a contact area between a specimen and pressure bars instead of a cylindrical specimen. The compressive experiments at various strain rates are conducted by using a hollow specimen.

Effect of Pre-Fatigue Deformation under Humid Environment on Impact Tensile Properties in 7075 Aluminum Alloys

The effect of pre-fatigue deformation in a humid environment on the impact tensile properties of 7075 aluminum alloys was investigated. An impact tensile test of the pre-fatigue deformed specimens was performed by means of the Split Hopkinson pressure bar method. Within the author’s set of experiments, the flow stress was unaffected by the pre-fatigue deformation. On the other hand, it was shown that the ductility of the pre-fatigue specimen was slightly lower than that of the non-fatigue specimen in the impact test. Additionally, the pre-fatigue specimen in a high-humidity environment had a lower ductility than in a low-humidity environment. It is thought that the decrease in ductility occurred due to changes in the microstructure, such as dislocations caused by the presence of hydrogen in the specimen due to pre-fatigue deformation in a high-humidity environment.

Impact Compressive Properties of Foamed Film with Closed Cell

The compressive properties of foamed polyethylene (PE) film with a closed cell for electronic devices have been investigated. A commercial closed cell foamed PE film with a density of 330 kg/m3 was used. Quasi-static testing was carried out at strain rates of 10−3 to 10−1 s−1. The strain rate of the impact test was approximately 105 s−1 by means of split Hopkinson pressure bar method. Within the set of experiments, the compressive stress increased with the strain rate in both the quasi-static and impact test. In particular, the flow stress increased substantially with the increasing strain rate in the impact deformation. At strains of less than 0.4, the trapped air was locally compressed within the cells, which led to the strain rate dependency of strength in the quasi-static test and the impact test.

Stress gage system for measuring very soft materials under high rates of deformation

Soft materials have seen continued growth in industrial importance, but are difficult to test at relevant, particularly at high, rates of deformation and relevant temperatures. This is mainly due to the low stresses supported by these materials, which mean that very sensitive force measurements are required. In this paper, a split-Hopkinson pressure bar method for testing very soft materials and elastomers at high rates of deformation is presented and applied. Experiments are conducted in compression on hydroxyl terminated polybutadiene, a very soft rubber, at strain rates of about 2000 s−1. Titanium alloy bars are used, and in addition to the usual strain gauges on the bars, forces at both ends of the specimen are measured using a piezoelectric material, lead zirconium titanate (PZT), which is much more sensitive than the quartz crystal gauges typically used in previous literature. The piezoelectric constant of PZT ranges between 290–630 × 10−12 C N−1, making it 100 times more sensitive than quartz crystal (2.3 × 10−12 C N−1). Results obtained from the experiments show that the gauges are able to measure the forces on both ends of the specimen with excellent signal to noise ratios.

OS1702 7075アルミニウム合金の予疲労誘起延性低下に及ぼすひずみ速度の影響

In this study, the tensile properties of the quasi-static and the impact tests for 7075 aluminum alloys subjected to pre-fatigue deformation in a humid environment were investigated. An impact tensile test was performed by means of the Split Hopkinson pressure bar method. The flow stress in both the quasi-static and the impact tests was unaffected by the pre-fatigue deformation. On the other hand, it was clarified that the ductility of the pre-fatigue specimen was slightly lower than that of the non-fatigue specimen. The ductility of the quasi-static test was decreased as compared with the impact test. It is thought that the ductility loss occurred due to changes in the microstructure, such as dislocations caused by the presence of hydrogen in the specimen due to pre-fatigue deformation in a high-humidity environment.