• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.7
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• pp.1073-1081
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• 2001

Many researches have published numerous papers about the high-strain-rate obtained from Split Hopkinson Pressure Bar(SHPB) tests. And 6.5wt%Si steel is widely known as an excellent magnetic material because its magnetostriction is nearly zero. Single crystals are prepared by the Floating Zone(FZ) method, which melts the alloy by the use of a high temperature electron beam in a pure argon gas condition. In this paper, the fracture behavior of the poly crystals and single crystals (DO$_3$phase) of Fe-6.5wt%Si alloy by SHPB test is observed. The comparison of high-strain-rate results with static results was done. Obtained main results are as follows: (1) Fe-6.5wt%Si alloy has higher strength at high-strain-rate tensile. SHPB results of polycrystal are twice as high as static results. (2) From the fractography, the cleavage steps are remarkably reduced in the SHPB test compared with the static test.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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• pp.559-564
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it is utilized in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. Accurate understanding of material's mechanical properties with various strain rates is required in order to guarantee the reliability of structural parts made of INCONEL 718. This paper is concerned with the dynamic material properties of the INCONEL 718 at various strain rates. The dynamic response of the INCONEL 718 at the intermediate strain rate is obtained from the high speed tensile test and at the high strain rate is from the split Hopkinson pressure bar test. The effect of the strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure is evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of rNCONEL 718.

• Composites Research
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• v.35 no.3
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• pp.196-200
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• 2022

Split Hopkinson Pressure Bar (SHPB) is a general test equipment for measuring the mechanical properties of high modulus metal and composite materials at high strain rate. However, for the soft plastic material, it is difficult to hold the specimen and achieve dynamic stress equilibrium due to the weak transmitted signals. In this study, SHPB test apparatus were designed to measure accurately the high strain rate stress-strain curve of the soft plastic materials by changing the incident bar materials and the shape of the specimen holder parts. In addition, to verify the high strain-rate tensile strain data obtained from SHPB, the strain distribution of the specimen was measured and analyzed with a high-speed camera and the digital image correlation (DIC), which was compared with the strain history measured from SHPB.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.256-259
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• 2004

In the present study, AZ31B sheets has a bad formability in room temperature, but the formability is improved significantly as increasing the temperature because of rolled magnesium alloy sheet has a hexagonal closed packed structure (HCP) and a plastic anisotropy. In this paper, after tensile test in various temperatures, strain rate, show the tensile mechanical properties, yield and ultimate strength, K-value, work hardening exponent(n), strain rate sensitivity(m). As temperature increased, yield, ultimate strength and K-value, work hardening exponent(n) are decreased but strain rate sensitivity(m) is increased. As cross-head-speed increased, yield, ultimate strength and K-value, work hardening exponent(n) are increased. And according to the temperature, how change the plastic anisotropy factor R. In addition, we observed how temperatures and cross-head-speed effect on microstructure.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.492-497
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• 2017

In this study, we investigated the effect of thermal aging on mechanical characteristics of Inconel 600 nickel-based alloy. The thermal aging was conducted up to 1000 hours at an atmosphere of $650^{\circ}C$. The microstructure of thermally aged specimens was investigated by an optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). In addition, tensile test (strain rate: 2 mm/min) and micro Vickers hardness test were conducted to evaluate mechanical properties with time. As a result of the experiment, Cr-rich carbide continuously precipitated during thermal aging, leading to the change of the mechanical characteristics and fracture mode. With the increase of aging time, tensile strength, yield strength, and hardness gradually decreased. The fracture mode changed from ductile to brittle with the increase of grain boundary carbide.

• Structural Engineering and Mechanics
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• v.69 no.1
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• pp.43-50
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• 2019

In this research, the effect of bedding layer on the tensile failure mechanism of rocks has been investigated using PFC2D. For this purpose, firstly calibration of PFC2d was performed using Brazilian tensile strength. Secondly Brazilian test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Totally, 21 model were simulated and tested by loading rate of 0.016 mm/s. The results show that when layer angle is less than 15, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilizes in failure process. Also, the failure trace is very short. It's to be noted that number of cracks decrease with increasing the layer thickness. Also, Brazilian tensile strength is minimum when bedding layer angle is between $45^{\circ}$ and $75^{\circ}$. The maximum one is related to layer angle of $90^{\circ}$.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.6
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• pp.857-866
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• 2013

This paper is concerned with the material properties of functional high explosive(FHX) simulant at various strain rates ranging from $10^{-4}/sec$ to $10^1/sec$. Material properties of FHX at high strain rates are important in prediction of deformation modes of FHX in a warhead which undergoes dynamic loading. Inert FHX stimulant which has analogous mechanical properties with FHX was utilized for material tests due to safety issues. Uniaxial tensile tests at quasi-static strain rates ranging from $10^{-4}/sec$ to $10^{-2}/sec$ and intermediate strain rates ranging from $10^{-1}/sec$ to $10^1/sec$ were conducted with JANNAF specimen using a tensile testing machine, INTRON 5583, and developed high speed material testing machine, respectively. Uniaxial compressive tests at quasi-static strain rates and intermediate strain rates were conducted with cylindrical specimen using a dynamic materials testing machine, INSTRON 8801. And cyclic compressive loading tests were performed with various strain rates and strains. Deformation behaviors were investigated using captured images obtained from a high-speed camera.

• Korean Journal of Metals and Materials
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• v.49 no.3
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• pp.211-220
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• 2011

To improve the low ductility and high strain-rate sensitivity in Sn-Bi based solder alloys, the influences of the minor additions of alloying elements (Ag, Mn, In) were investigated. The strain-stress curves of various Sn-40Bi(-X) alloys, including a pre-suggested Sn-40Bi-0.1Cu composition were measured using a tensile testing machine. As a result, the elongation and ultimate tensile strength (UTS) values were compared. The small addition (0.5 wt.%) of Ag significantly enhanced the ductility and high strain-rate sensitivity of the alloys at strain rates of $10^{-4}$ to $10^{-2}\;s^{-1}$ mainly due to the increase and refinement of eutectic lamellar structures. The microstructure change increased the area of grain boundaries, thus ameliorating the grain boundary sliding mode. It was also found that Mn is an effective element in enhancing the ductility, especially at the strain rates of $10^{-3}$ to $10^{-2}\;s^{-1}$ The enhancement is likely attributed to the fine and homogeneous microstructure in the alloys containing Mn.

• Nuclear Engineering and Technology
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• v.48 no.5
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• pp.1252-1263
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• 2016

This paper presents a numerical method to simulate ductile tearing in cracked components under high strain rates using finite element damage analysis. The strain rate dependence on tensile properties and multiaxial fracture strain is characterized by the model developed by Johnson and Cook. The damage model is then defined based on the ductility exhaustion concept using the strain rate dependent multiaxial fracture strain concept. The proposed model is applied to simulate previously published three cracked pipe bending test results under two different test speed conditions. Simulated results show overall good agreement with experimental results.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.615-624
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• 2010

This study is concerned with tensile and Charpy impact properties of high-strength bainitic steels fabricated by controlled rolling process. Six kinds of steels were fabricated by varying finish rolling temperature, start cooling temperature, and cooling rate, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron backscatter diffraction analysis. The microstructures of the steels rolled in the single phase region were most similar to those of the steels rolled in the two phase region. The steels cooled from $700{^{\circ}C}$ were composed mainly of granular bainites, while those cooled from $600{^{\circ}C}$ contained a number of bainitic ferrites, which resulted in the decrease in ductility and upper shelf energy in spite of the increase in strength. In the steels cooling from $600^{\circ}C$, fine acicular ferrites were well formed when the cooling rate was slow, which led to the best combination of high ductility, high upper shelf energy, and low energy transition temperature according to the decrease in the overall effective grain size due to the presence of acicular ferrites having smaller effective grain size.