• 한국자동차공학회논문집
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• 제10권2호
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• pp.96-100
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• 2002

The purpose of this paper is presented a rational method of predicting dynamic/impact tensile strength of high tensile steel materials widely used fur structural material of automobiles. It is known that the ultimate strength is related with the loading speed and the Lethargy Coefficient from the tensile test. The Dynamic Lethargy Coefficient is proportional to the disorientation of the molecular structure and indicates the magnitude of defects resulting from the probability of breaking the bonds responsible for its strength. The coefficient is obtained from the simple tensile test such as failure time and stresses at fracture. These factors not only affect the static strength but also have a great influence on the dynamic/impact characteristics of the joist and the adjacent structures. This strength is used to analyze the failure life prediction of mechanical system by virtue of its material fracture. The impact tensile test is performed to evaluate the life parameters due to loading speed with the proposed method. Also the evaluation of the dynamic/impact effect on the material tensile strength characteristics is compared with the result of Campbell-Cooper equation to verify the proposed method.

• 한국안전학회지
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• 제27권6호
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• pp.7-13
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• 2012

A lack of study on the dynamic tensile strengths of Sn-based solder joints at high strain rates was the motivation for the present study. A modified miniature Charpy impact testing machine instrumented with an impact sensor was built to quantitatively evaluate the dynamic impact strength of a solder joint under tensile impact loading. This study evaluated the tensile strength of lead-free solder ball joints at strain rates from $1.8{\times}10^3s^{-1}$ and $8.5{\times}10^3s^{-1}$. The maximum tensile strength of the solder ball joint decreases as the load speed increases in the testing range. This tensile strength represented that of the interface because of the interfacial fracture site. The tensile strengths of solder joints between Sn-3.0Ag-0.5Cu and copper substrate were between 21.7 MPa and 8.6 MPa in the high strain range.

• Computers and Concrete
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• 제26권3호
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• pp.275-283
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• 2020

Reinforced concrete (RC) does not provide sufficient resistance against impacts and blast loads, and the brittle structure of RC fails to protect against fractures due to the lack of shock absorption. Investigations on improving its resistance against explosion and impact have been actively conducted on high-performance fiber-reinforced cementitious composites (HPFRCCs), such as fiber-reinforced concrete and ultra-high-performance concrete. For these HPFRCCs, however, tensile strength and toughness are still significantly lower compared to compressive strength due to their limited fiber volume fraction. Therefore, in this study, the tensile behavior of slurry-infiltrated fiber-reinforced cementitious composites (SIFRCCs), which can accommodate a large number of steel fibers, was analyzed under static and dynamic loading to improve the shortcomings of RC and to enhance its explosion and impact resistance. The fiber volume fractions of SIFRCCs were set to 4%, 5%, and 6%, and three strain rate levels (maximum strain rate: 250 s^-1) were applied. As a result, the tensile strength exceeded 15 MPa under static load, and the dynamic tensile strength reached a maximum of 40 MPa. In addition, tensile characteristics, such as tensile strength, deformation capacity, and energy absorption capacity, were improved as the fiber volume fraction and strain rate increased.

• Geomechanics and Engineering
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• 제23권5호
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• pp.467-480
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• 2020

The failure behavior and tensile strength of sandstone materials under different strain rates are greatly different, especially under static loads and impact loads. In order to clearly investigate the failure mechanism of sandstone materials under static and impact loads, a series of Brazilian disc samples were used by employing green sandstone, red sandstone and black sandstone to carry out static and impact loading splitting tensile tests, and the failure properties subjected to two different loading conditions were analyzed and discussed. Subsequently, the failure behavior of sandstone materials also were simulated by finite element code. The good agreement between simulation results and experimental results can obtain the following significantly conclusions: (1) The relationship of the tensile strength among sandstone materials is that green sandstone < red sandstone < black sandstone, and the variation of the tensile sensitivity of sandstone materials is that green sandstone > red sandstone > black sandstone; (2) The mainly cause for the difference of dynamic tensile strength of sandstone materials is that the strength of crystal particles in sandstone material, and the tensile strength of sandstone is proportional to the fractal dimension; (3) The dynamic failure behavior of sandstone is greatly different from that of static failure behavior, and the dynamic tensile failure rate in dynamic failure behavior is about 54.92%.

• 한국구조물진단유지관리공학회 논문집
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• 제22권3호
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• pp.31-37
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• 2018

이 논문은 압축강도 수준(100, 140, 180 MPa급)에 따른 HPFRCC의 동적충격 인장강도를 평가하였다. 먼저 100, 140, 180 MPa급 HPFRCC의 압축응력-변형률 관계를 분석한 결과 압축강도는 각각 112, 150, 202 MPa로 나타났으며, 압축강도가 높아짐에 따라 탄성계수도 증가하는 경향을 나타내었다. 100, 140, 180 MPa급 HPFRCC의 정적 인장강도는 각각 10.7, 11.5, 16.5 MPa로 나타났으며, 압축강도가 높아질수록 인장강도도 증가하는 경향을 나타내었다. 반면 100 및 140 MPa급 HPFRCC에서의 인장강도 및 에너지 흡수능력은 압축강도 수준에 따라 큰 차이를 보이지 않았다. 이는 시험체의 규격 및 강섬유의 배열에 영향을 받은 것으로 판단된다. HPFRCC의 동적충격 인장강도를 평가한 결과, 변형률 속도가 10-1/s에서 150/s로 증가할수록 모든 HPFRCC의 인장강도와 동적증가계수는 증가하는 경향을 보였다. 한편 동일한 범위의 변형률 속도에서 HPFRCC의 압축강도가 낮을수록 인장강도에 대한 DIF가 높게 측정되어 효율적인 측면에서는 100 MPa급 HPFRCC가 가장 우수한 것으로 나타났다. 따라서 높은 수준의 인장성능이 요구되는 경우 높은 압축강도를 가지는 HPFRCC를 사용하는 것이 유리하며, 폭발과 같은 고속변형률 속도에서 보다 효율적인 접근을 위해서는 목표 압축강도에 근접한 HPFRCC를 사용하는 것이 바람직한 것으로 판단된다.

• Advanced Composite Materials
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• 제17권2호
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• pp.139-156
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• 2008

This study aims to characterize the dynamic tensile strength of unidirectional carbon/epoxy composites. Two different carbon/epoxy composite systems, the unidirectional T700S/2500 and TR50S/modified epoxy, are tested at the static condition and the strain rate of $100\;s^{-1}$. A high-strain-rate test was performed using a tension-type split Hopkinson bar technique with a specific fixture for specimen. The experimental results demonstrated that both tensile strength increase with strain rate, while the fracture behaviors are quite different. By the use of the rosette analysis and the strain transformation equations, the strain rate effects of material principal directions on tensile strength are investigated. It is experimentally found that the shear strain rate produces the more significant contribution to strain rate effect on dynamic tensile strength. An empirical failure criterion for characterizing the dynamic tensile strength was proposed based on the Hash-in's failure criterion. Although the proposed criterion is just the empirical formula, it is in better agreement with the experimental data and quite simple.

• Advances in concrete construction
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• 제13권 2호
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• pp.123-132
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• 2022

This paper aims to adapt Multilinear regression (MLR) to predict the strength and toughness of SIFCON containing various pozzolanic materials. Slurry Infiltrated Fibrous Concrete (SIFCON) is one of the most common terms used in concrete manufacturing, known for its benefits such as high ductility, toughness and high ultimate strength. Assessment of compressive strength (CS.), flexural strength (F.S.), splitting tensile strength (STS), dynamic elasticity modulus (DME) and impact energy (I.E.) using the experimental approach is too costly. It is time-consuming, and a slight error can lead to a repeat of the test and, to solve this, alternative methods are used to predict the strength and toughness properties of SIFCON. In the present study, the experimentally investigated SIFCON data about various mix proportions are used to predict the strength and toughness properties using regression analysis-multilinear regression (MLR) models. The input parameters used in regression models are cement, fibre, fly ash, Metakaolin, fine aggregate, blast furnace slag, bottom ash, water-cement ratio, and the strength and toughness properties of SIFCON at 28 days is the output parameter. The models are developed and validated using data obtained from the experimental investigation. The investigations were done on 36 SIFCON mixes, and specimens were cast and tested after 28 days of curing. The MLR model yields correlation between predicted and actual values of the compressive strength (C.S.), flexural strength, splitting tensile strength, dynamic modulus of elasticity and impact energy. R-squared values for the relationship between observed and predicted compressive strength are 0.9548, flexural strength 0.9058, split tensile strength 0.9047, dynamic modulus of elasticity 0.8611 for impact energy 0.8366. This examination shows that the MLR model can predict the strength and toughness properties of SIFCON.

• 대한기계학회논문집
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• 제17권7호
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• pp.1772-1782
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• 1993

The characteristics of metal matrix composite under dynamic tension at high strain rates up to the order of $10^3/sec$ is studied by using newly developed apparatus. The composite material processed in this research is aluminum-alumina metal matrix composites, arid fabricated by compocasting with the fiber volume fraction from 5 to 20%. The whisker and matrix material used in this paper were ${\delta}-Al_2O_3$ and Al-6061, respectively. The mechanical tests performed in this research are low and high strain rate tensile test. At low strain-rate tensile test, the modulus of elasticity and the ultimate tensile strength of the composites were improved about 77 pct. and 55 pct., respectively comparing with the unreinforced materials. At strain-rate from $10^{-3}\;to\;10^3/s$, the effect of strain-rate on the modulus, ultimate strength, flow stress is determined. Also the effect of strain rate on the modulus, ultimate tensile strength, flow stress and elongation to failures were investigated.

• Advanced Composite Materials
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• 제16권2호
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• pp.167-180
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• 2007

The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress-strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai-Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the above failure criterion under dynamic loading conditions.

• 복식문화연구
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• 제21권6호
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• pp.967-973
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• 2013

During high speed sewing, the needle thread is exposed to dynamic loading, short strike loading, inertia forces, friction, rubbing, force of check spring, bending, pressure, friction, impact, shock and thermal influence. The dynamic thread loading/tension alters throughout the stitch formation cycle and along its passage through the machine. The greatest tensile force occurs at the moment of stitch stretching, when the take up lever pulls for required thread length through the tension regulator. These stresses act on the thread repeatedly and the thread passes 50-80 times through the fabric, the needle eye and the bobbin case mechanism, before getting incorporated into the seam, which result in upto 40% loss in tensile strength of the sewing thread. This damage in the sewing thread adversely affects its processing and functional performance. In this paper, the contribution of dynamic loading, passage through needle and fabric, and bobbin thread interaction in the loss in tensile properties has been studied. It is observed that the loss in tensile properties occurs mainly due to the bobbin thread interaction. Dynamic loading due to the action of take up lever also causes substantial loss in tenacity and breaking elongation of cotton threads.