Modified Equivalent Radius Approach in Evaluating Stress-Strain Relationship in Torsional Test

배윤신 한국방재학회 2008 한국방재학회논문집 Vol.8 No.2

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship. Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

Determination of true stress-strain curve of type 304 and 316 stainless steels using a typical tensile test and finite element analysis

Kweon, Hyeong Do,Kim, Jin Weon,Song, Ohseop,Oh, Dongho Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.2

Knowing a material's true stress-strain curve is essential for performing a nonlinear finite element analysis to solve an elastoplastic problem. This study presents a simple methodology to determine the true stress-strain curve of type 304 and 316 austenitic stainless steels in the full range of strain from a typical tensile test. Before necking, the true stress and strain values are directly converted from engineering stress and strain data, respectively. After necking, a true stress-strain equation is determined by iteratively conducting finite element analysis using three pieces of information at the necking and the fracture points. The Hockett-Sherby equation is proposed as an optimal stress-strain model in a non-uniform deformation region. The application to the stainless steel under different temperatures and loading conditions verifies that the strain hardening behavior of the material is adequately described by the determined equation, and the estimated engineering stress-strain curves are in good agreement with those of experiments. The presented method is intrinsically simple to use and reduces iterations because it does not require much experimental effort and adopts the approach of determining the stress-strain equation instead of correcting the individual stress at each strain point.

Estimation of the Small-Strain Stiffness of Clean and Silty Sands using Stress-Strain Curves and CPT Cone Resistance

Lee, Junhwan,Kyung, Doohyun,Kim, Bumjoo,Prezzi, Monica Elsevier 2009 Soils and foundations Vol.49 No.4

<P><B>ABSTRACT</B></P> <P>The initial, linear elastic range of a soil stress-strain curve is often defined by the small-strain elastic modulus <I>E</I> <SUB>0</SUB> or shear modulus <I>G</I> <SUB>0</SUB>. In the present study, simpler and effective methods are proposed for the estimation of the small-strain stiffness of clean and silty sands; these are based on triaxial compression test results and the CPT cone resistance <I>q</I> <SUB>c</SUB>. In the method based on stress-strain curves obtained from triaxial compression tests, an extrapolation technique is adopted within the small-strain range of a transformed stress-strain curve to obtain estimates of the small-strain elastic modulus. Calculated small-strain elastic modulus values were compared with the values measured using bender element tests performed on clean sands and sands containing nonplastic fines. The results showed that the method proposed produces satisfactory estimates of the small-strain elastic modulus for practical purposes. In the CPT-based method, two <I>G</I> <SUB>0</SUB>-<I>q</I> <SUB>c</SUB> correlations available in the literature were evaluated. For isotropic conditions, both correlations produced reasonably good estimates of <I>G</I> <SUB>0</SUB> for clean sands but overestimated it for silty sands. A <I>G</I> <SUB>0</SUB>-<I>q</I> <SUB>c</SUB> correlation which is proposed takes into account the effect of silt content of the sand and stress anisotropy.</P>

비선형 수치해석을 위한 모아쿨롱 매개정수와 응력변형률 곡선에 관한 연구

김형준,이완훈 한국도로학회 2024 한국도로학회논문집 Vol.26 No.2

PURPOSES : Concrete, which is a construction material, is the most widely used compression material; however, unlike steel, it exhibits nonlinear material characteristics. Therefore, to examine the behavior of structures under the nonlinear conditions of concrete materials, one must select an appropriate numerical-analysis technique and a reasonable material model. When performing the nonlinear numerical analysis of a structure using general-purpose structural analysis software, the stress–strain curve or the Mohr–Coulomb failure criterion is typically employed to consider the nonlinear material characteristics. In this study, an efficient nonlinear numerical analysis is conducted by defining the stress–strain curves and Mohr–Coulomb parameters applicable to Strand7 to examine and design the stability of reinforced concrete structures. METHODS : This study was conducted by improving existing data. Based on the tensile region of the concrete stress–strain curve presented in a simple shape and the results of the splitting test, the proposed Mohr–Coulomb parameter was improved based on regulations stipulated in the design standards of concrete structures. The characteristics and usability of the improved material models were examined using concrete splitting tensile and bending models. RESULTS : A yield area distribution similar to that of the reference data is obtained when the Mohr–Coulomb material model is used in the numerical analysis of the concrete splitting tension, thus confirming the validity of the model. In the Mohr–Coulomb material model, nonlinear resistance continues even after the maximum reaction force occurs. However, when the stress–strain curve material model is applied, at the moment the maximum reaction force occurs, the material yields and begins to be damaged. In addition, by applying the Mohr–Coulomb material model to the bending numerical-analysis model, the magnitude of stress in the tensile region from the initial stage exceeds the yield stress defined in the stress–strain curve. CONCLUSIONS : Based on a series of examples, the usability of the proposed concrete stress–strain curve and Mohr–Coulomb parameters is confirmed. However, to obtain numerical-analysis results that are consistent with the nonlinear behavior of actual structures, nonlinear testing of reinforced concrete structures shall be conducted and material models shall be improved.

비등방 압밀된 다짐화강풍화토의 응력-변형률 거동 예측

정진섭 ( Jeong Jin Seob ),양재혁 ( Yang Jae Hyouk ) 한국농공학회 2003 韓國農工學會誌 : 전원과 자원 Vol.45 No.2

During this study, constant stress ratio tests with previous compression anisotropic stress history are performed on compacted decomposed granite soil sampled at Iksan, Jeonbuk. Yielding points are determined from stress-strain curves. The shape and characteristics of compression anisotropic yield curves is examined. In addition, the measured value of yielding curve and stress-strain behavior is predicted by Yasufuku's anisotropic constitutive model based on non-associated flow rule. The main results are summarized as follows : 1) Shape of yielding curves shows almost ellipse but asymmetry with respect to stress path during previous consolidation stress. 2) Yasufuku's anisotropic constitutive model is suitable in evaluation of yielding curves on anisotropic consolidated decomposed granite soil. 3) The predicted stress-strain curve shows reasonable agreement to measured behaviours.

Stress-strain behavior and toughness of high-performance steel fiber reinforced concrete in compression

P. Ramadoss,K. Nagamani 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.11 No.2

The complete stress-strain behavior of steel fiber reinforced concrete in compression is needed for the analysis and design of structures. An experimental investigation was carried out to generate the complete stress-strain curve of high-performance steel fiber reinforced concrete (HPSFRC) with a strength range of 52–80 MPa. The variation in concrete strength was achieved by varying the water-to-cementitious materials ratio of 0.40-0.25 and steel fiber content (Vf = 0.5, 1.0 and 1.5% with l/d = 80 and 55) in terms of fiber reinforcing parameter, at 10% silica fume replacement. The effects of these parameters on the shape of stress-strain curves are presented. Based on the test data, a simple model is proposed to generate the complete stress-strain relationship for HPSFRC. The proposed model has been found to give good correlation with the stress-strain curves generated experimentally. Inclusion of fibers into HPC improved the ductility considerably. Equations to quantify the effect of fibers on compressive strength, strain at peak stress and toughness of concrete in terms of fiber reinforcing index are also proposed, which predicted the test data quite accurately. Compressive strength prediction model was validated with the strength data of earlier researchers with an absolute variation of 2.1%.

등방 및 비등방 압밀된 다짐풍화화강토의 항복곡선

정진섭 ( Jeong Jin Seob ),양재혁 ( Yang Jae Hyouk ) 한국농공학회 2002 韓國農工學會誌 : 전원과 자원 Vol.44 No.1

During this study, various stress path tests in previous isotropic and anisotropic (compression and tension) stress histories are performed on weathered granite soil sampled at Iksan, Jeonbuk. Yielding points are determined from various stress-strain curves(stress ratio-shear strain, volumetric strain, normalized energy and dissipated total energy curves). The shape and characteristics of isotropic and anisotropic yielding curves are examined. The main results are summarized as follows : 1) Yielding curves defined from stress ratio - normarized energy and dissipated total energy curves show almost perfect ellipse. 2) Directions of plastic strain incremental vector are not perpendicular to yielding curve. 3) Normarized energy and dissipated total energy spread with similar tendency with respect to yielding curve in stress space.

지진하중 조건의 비선형 유한요소해석에서 반복경화 거동고려를 위한 Bi-linear 응력-변형률 곡선

정현준,김진원,김종성,구경회 한국압력기기공학회 2018 한국압력기기공학회 논문집 Vol.14 No.2

This study compares true stress-true strain curves obtained by tensile tests of various piping materials with bi-linear stress-strain approximation suggested in the JSME Code Case(CC) Draft, a guideline for piping seismic inelastic response analysis. Based on the comparisons, the reliability of the bi-linear approximation is evaluated. It is found that bi-linear stress-strain curve of TP316 stainless steel is in good agreement with its true stress-true strain curve. However, Bi-linear stress-strain curves of TP304 stainless steel and carbon steels determined by the approximation cannot appropriately estimate their stress-strain behavior. Accordingly new bi-linear approximations for carbon steels and low-alloy steels are proposed. The proposed bi-linear approximations for carbon and low-alloy steels, which include the temperature effect on strength and hardening of material, estimate their stress-strain behavior reasonably well.

Tensile Behavior and Full-range Stress-Strain Curves for Gr. 91 Steel

Woo-Gon Kim(김우곤),Jae-Young Park(박재영),I.M.W. Ekaputra,Hyeong-Yeon Lee(이형연),Seon-Jin Kim(김선진) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

High-temperature tensile behavior for Grade 91 (Gr. 91) steel for use of a sodium-cooled fast reactor (SFR) structure was investigated, and full-range stress-strain curves were described in terms of RCC-MRx procedures (French SFR code) and four constitutive equations: power-law form, logarithmic form, exponential form, and modified form (powerlaw + exponential). To do this, a series of high-temperature tensile data was obtained from the tensile tests performed with a strain rate of 6.67 x10-4 (1/s) at R.T to 650oC. On the basis of experimental tensile data, full-range stress-strain curves were designed by RCC-MRx procedures. In addition, a modified constitutive equation in terms of a combination of power-law form and exponential form were proposed to well describe the full-range stress-strain curves, and the suitable equation in the four equations was investigated by fitting to the experimental curves. Results showed that the stress-strain curves designed by RCC-MRx were in accordance with the experimental curves at all of the temperature ranges, and a proposed modified equation was found to be superior in modeling of the stress-strain curves to the other equations. It can be conveniently used in modeling full-range stress-strain curves without calculation procedures in RCC-MRx code.

LSTM 순환 신경망을 이용한 재료의 단축하중 하에서의 응력-변형률 곡선 예측 연구

변훈(Hoon Byun),송재준(Jae-Joon Song) 한국암반공학회 2018 터널과지하공간 Vol.28 No.3

이 논문에서는 재료의 단축하중 하에서의 응력-변형률 곡선을 예측하기 위하여 순환 신경망의 일종인 LSTM(Long Short-Term Memory) 알고리즘을 사용하였다. 석고와 규사를 혼합해 만든 재료에 일축압축시험을 수행하여 얻은 응력-변형률 데이터를 이용하였으며, 낮은 응력 구간의 초반 데이터를 활용해서 파괴 전까지의 거동을 예측하였다. 앞부분의 데이터를 활용하여 단계적으로 뒤쪽 구간의 값을 예측하는 LSTM 순환 신경망의 구조상 큰 응력에 대응하는 변형률을 예측할 경우에는 앞쪽 구간의 오차가 누적되어 실측값과 차이가 늘어났으나 전반적으로 높은 정확도로 응력-변형률 곡선을 예측하였다. 예측에 사용한 초기 데이터의 길이가 늘어나는 경우 정확도는 조금 증가했다. 그러나 접선을 이용한 단순 예측과의 성능 차이는 초기 데이터의 길이가 작은 경우에 두드러졌으며, 적은양의 데이터로도 응력-변형률 곡선 전체 구간의 예측을 가능하게 한다는 점으로부터 신경망 모델의 필요성을 확인하였다. LSTM (Long Short-Term Memory) algorithm which is a kind of recurrent neural network was used to establish a model to predict the stress-strain curve of an material under uniaxial compression. The model was established from the stress-strain data from uniaxial compression tests of silica-gypsum specimens. After training the model, it can predict the behavior of the material up to the failure state by using an early stage of stress-strain curve whose stress is very low. Because the LSTM neural network predict a value by using the previous state of data and proceed forward step by step, a higher error was found at the prediction of higher stress state due to the accumulation of error. However, this model generally predict the stress-strain curve with high accuracy. The accuracy of both LSTM and tangential prediction models increased with increased length of input data, while a difference in performance between them decreased as the amount of input data increased. LSTM model showed relatively superior performance to the tangential prediction when only few input data was given, which enhanced the necessity for application of the model.