• Journal of Magnetics
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• 제16권4호
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• pp.427-430
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• 2011

The rolled steels for welded structure applied tensile stress have been examined by means of magnetic Barkhausen noise (MBN) method and of a physical parameter obtained from a hysteresis loop. The behaviors of MBN parameters and coercive force with tensile stress were discussed in relation to microstructure changes. There is no change in MBN parameters and coercive force below yield strength. The coercive force rises rapidly with tensile stress above yield strength. On the other hand, the rms voltage and the peak in averaged rms voltage take a maximum around yield strength and then decreases. The magnetomotive force at peak in the averaged rms voltage shows a minimum around yield strength. These phenomena are attributed to the combined effects of cell texture and dislocation density. In addition, the behaviors of MBN parameters around yield strength may be reflected by the localized changes in strain field due to the formation of dislocation tangles.

• Geomechanics and Engineering
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• 제17권4호
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• pp.333-342
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• 2019

Geological dynamic hazards during coal mining can be caused by the failure of a composite system consisting of roof rock and coal layers, subject to different loading rates due to different advancing velocities in the working face. In this paper, the uniaxial compression test simulations on the composite rock-coal layers were performed using $PFC^{2D}$ software and especially the effects of loading rate on the stress-strain behavior, strength characteristics and crack nucleation, propagation and coalescence in a composite layer were analyzed. In addition, considering the composite layer, the mechanisms for the advanced bore decompression in coal to prevent the geological dynamic hazards at a rapid advancing velocity of working face were explored. The uniaxial compressive strength and peak strain are found to increase with the increase of loading rate. After post-peak point, the stress-strain curve shows a steep stepped drop at a low loading rate, while the stress-strain curve exhibits a slowly progressive decrease at a high loading rate. The cracking mainly occurs within coal, and no apparent cracking is observed for rock. While at a high loading rate, the rock near the bedding plane is damaged by rapid crack propagation in coal. The cracking pattern is not a single shear zone, but exhibits as two simultaneously propagating shear zones in a "X" shape. Following this, the coal breaks into many pieces and the fragment size and number increase with loading rate. Whereas a low loading rate promotes the development of tensile crack, the failure pattern shows a V-shaped hybrid shear and tensile failure. The shear failure becomes dominant with an increasing loading rate. Meanwhile, with the increase of loading rate, the width of the main shear failure zone increases. Moreover, the advanced bore decompression changes the physical property and energy accumulation conditions of the composite layer, which increases the strain energy dissipation, and the occurrence possibility of geological dynamic hazards is reduced at a rapid advancing velocity of working face.

• Structural Engineering and Mechanics
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• 제47권4호
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• pp.531-544
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• 2013

Compared with pavement structures of ordinary road sections, pavement structures in the intersection are exposed to more complex traffic characteristics which may exacerbates pavement distresses such as fatigue-cracking, shoving, shear deformation and rutting. Based on a field survey about traffic characteristics in the intersection conducted in Shanghai China, a three dimensional dynamic finite-element model was developed for evaluating the mechanistic responses in the pavement structures under different traffic characteristics, namely uniform speed, acceleration and deceleration. The results from this study indicated that : (1) traffic characteristics have significant effects on the distributions of the maximum principal strain (MPS) and the maximum shear stress (MSS) at the pavement surface; (2) vehicle acceleration or deceleration substantially impact the MPS and MSS at pavement surface and could increase the magnitude of them by 20 percent to 260 percent; (3) in the vertical direction, with the increase of vehicle deceleration rate, the location of the MPS peak value and the MSS peak value changes from the sub-surface layer to the pavement surface.

• Earthquakes and Structures
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• 제7권5호
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• pp.647-665
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• 2014

Squat reinforced concrete walls require enough shear strength in order to promote flexural yielding, which creates the need for designers of an accurate method for strength prediction. In many cases, especially for existing buildings, strength estimates might be insufficient when more accurate analyses are needed, such as pushover analysis. In this case, estimates of load versus displacement are required for building modeling. A model is developed that predicts the shear load versus shear deformation of squat reinforced concrete walls by means of a panel formulation. In order to provide a simple, design-oriented tool, the formulation considers the wall as a single element, which presents an average strain and stress field for the entire wall. Simple material constitutive laws for concrete and steel are used. The developed models can be divided into two categories: (i) rotating-angle and (ii) fixed-angle models. In the first case, the principal stress/strain direction rotates for each drift increment. This situation is addressed by prescribing the average normal strain of the panel. The formation of a crack, which can be interpreted as a fixed principal strain direction is imposed on the second formulation via calibration of the principal stress/strain direction obtained from the rotating-angle model at a cracking stage. Two alternatives are selected for the cracking point: fcr and 0.5fcr (post-peak). In terms of shear capacity, the model results are compared with an experimental database indicating that the fixed-angle models yield good results. The overall response (load-displacement) is also reasonable well predicted for specimens with diagonal compression failure.

• Geomechanics and Engineering
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• 제30권1호
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• pp.93-105
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• 2022

With the exploitation of natural resources in China, underground resource extraction and underground space development, as well as other engineering activities are increasing, resulting in the creation of many defective rocks. In this paper, uniaxial compression tests were performed on rocks with double holes and fractures at different angles using particle flow code (PFC2D) numerical simulations and laboratory experiments. The failure behavior and mechanical properties of rock samples with holes and fractures at different angles were analyzed. The failure modes of rock with defects at different angles were identified. The fracture propagation and stress evolution characteristics of rock with fractures at different angles were determined. The results reveal that compared to intact rocks, the peak stress, elastic modulus, peak strain, initiation stress, and damage stress of fractured rocks with different fracture angles around holes are lower. As the fracture angle increases, the gap in mechanical properties between the defective rock and the intact rock gradually decreased. In the force chain diagram, the compressive stress concentration range of the combined defect of cracks and holes starts to decrease, and the model is gradually destroyed as the tensile stress range gradually increases. When the peak stress is reached, the acoustic emission energy is highest and the rock undergoes brittle damage. Through a comparative study using laboratory tests, the results of laboratory real rocks and numerical simulation experiments were verified and the macroscopic failure characteristics of the real and simulated rocks were determined to be similar. This study can help us correctly understand the mechanical properties of rocks with defects and provide theoretical guidance for practical rock engineering.

• Geomechanics and Engineering
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• 제13권1호
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• pp.63-77
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• 2017

The failure mechanism of a deep hard rock tunnel under high geostress and high geothermalactivity is extremely complex. Uniaxial compression tests of granite at different temperatures were conducted. The complete stress-strain curves, mechanical parameters and macroscopic failure types of the rock were analyzed in detail. The brittleness index, which represents the possibility of a severe brittleness hazard, is proposed in this paperby comparing the peak stress and the expansion stress. The results show that the temperature range from 20 to $60^{\circ}C$ is able to aggravate the brittle failure of hard rock based on the brittleness index. The closure of internal micro cracks by thermal stress can improve the strength of hard rock and the storage capacity of elastic strain energy. The failure mode ofthe samples changes from shear failure to tensile failure as the temperature increases. In conclusion, the brittle failure mechanism of hard rock under the action of thermal coupling is revealed, and the analysis result offers significant guidance for deep buried tunnels at high temperatures and under high geostress.

• 소성∙가공
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• 제3권4호
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• pp.427-439
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• 1994

The high temperature deformation behavior of $SiC_p/Al-Si$ composites and Al-Si matrix was studied by hot torsion test in a range of temperature from $270^{\circ}C$ to $520^{\circ}C$ and at strain rate range of $1.2{\times}10_{-3}~2.16{\times}10_{-1}/sec$. The hot restoration mechanisms for both matrix and composites were found to be dynamic recrystallization(DRX) from the investigation of flow curves and microstructural evolutions. The Si precipitates and SiC particles promoted DRX, and the peak strain$({\varepsilon}_p)$ of the composites was smaller than that of the matrix. Flow stresses of $SiC_p/Al-Si$ composites were found to be generally higher than the matrix, but the difference was quite small at higher temperature due to the decrease of capability of load transfer by SiC particles. With increasing temperature, failure strain of matrix and composites are inclined to increase, the increasing value of failure strain for the $SiC_p/Al-Si$ composites was small compared to that of matrix. The stress dependence of both materials on strain rate() and temperature(T) was examined by hyperbolic sine law, $\.{\varepsilon}=A_1[sinh({\alpha}{\cdot}{\sigma})]_n$exp(-Q/RT)

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.802-810
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• 2020

Three-dimensional finite element simulations are implemented for the in-pile thermo-mechanical behavior in U-Mo/Al monolithic fuel plates with different thermal creep rates of cladding involved. The numerical results indicate that the thickness increment of fuel foil rises with the thermal creep coefficient of cladding. The maximum Mises stress of cladding is reduced by ~85% from 344 MPa on the 98.0^th day when the creep coefficient of cladding increases from 0.01 to 10.0, due to its equivalent thermal creep strain enlarged by 3.5 times. When the thermal creep coefficient of Aluminum cladding increases from 0 to 1.0, the maximum mesoscale stress of fuel foil varies slightly. At the same time, the peak mesoscale normal stress of fuel foil can reach 51 MPa on the 98.0^th day for the thermal creep coefficient of 10, which increases by 60.3% of that with the thermal creep un-occurred in the cladding. The maximum through-thickness creep strain components of fuel foil differ slightly for different thermal creep coefficients of cladding. The dangerous region of fuel foil becomes much closer to the heavily irradiated side when the creep coefficient of cladding becomes 10.0. The creep performance of Aluminum cladding should be optimized for the integrity of monolithic fuel plates.

• Geomechanics and Engineering
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• 제20권3호
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• pp.221-232
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• 2020

In many tropical regions, soil structures often fail under constant loads as a result of decreasing matric suction due to water infiltration. Most of the previous studies have been performed by infiltrating water in the soil specimen by keeping shear stress constant at 85-90% of peak shear strength in order to ensure specimen failure during water infiltration. However, not many studies are available to simulate the soil behavior when water is infiltrated at lower shear stress and how the deformations affect the soil behavior if the failure did not occur during water infiltration. This research aimed at understanding both the strength and deformation behavior of unsaturated soil during the course of water infiltration at 25%, 50% and 75% of maximum deviatoric stress and axial strain by keeping them constant. A unique stress-strain curve expresses the transient situation from unsaturated condition to failure state due to water infiltration is also drawn. The shearing-infiltration test results indicate that the water infiltration reduces matric suction and increase soil deformation. This research also indicates that unsaturated soil failure problems should not always be treated as shear strength problems but deformation should also be considered while addressing the problems related to unsaturated soils.

• 콘크리트학회논문집
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• 제23권6호
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• pp.765-772
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• 2011

이 연구에서는 알칼리활성 슬래그 콘크리트의 응력-변형률 관계를 평가하기 위한 일련의 콘크리트 실린더의 압축 실험을 요약하였다. 실험된 콘크리트의 압축강도는 8.6 MPa에서 42.2 MPa의 범위이며, 단위용적질량은 $2,168kg/m^3$ 에서 $2,343kg/m^3$의 범위이다. 34개의 콘크리트 시험체에서 얻은 결과들에 근거하여 알칼리활성 슬래그 콘크리트의 응력-변형률 모델을 수학적으로 제시하였다. 콘크리트의 탄성계수, 최대응력 시 변형률 및 곡선의 상승부와 하강부의 기울기는 압축강도와 단위용적질량의 함수로 일반화하였다. 각 시험체에서 측정한 값과 제시된 모델의 예측값 사이에서 산정된 변동계수들의 평균과 표준편차는 각각 6.9%와 2.6%이었다. 따라서 제시된 모델은 보통포틀랜드 시멘트 콘크리트에서 제시된 다른 모델들에 비해 AA 슬래그 콘크리트의 응력-변형률 특성을 보다 더 정확하고 합리적으로 나타내었다.