Papers by Keyword: Stress-Strain Relationship

Abstract: This paper investigates the stress-strain relationship of a rectangular cross-section concrete element reinforced with Carbon fiber Sheet (CFS). In order to verify the confinement effect of the carbon fiber sheet over the concrete, an experiment was conducted using concrete elements with CFS by changing the ratio of side length of the cross section, the ratio of the height to the short side and the amount of CFS layers. In total, 16 concrete specimens were tested under compressive monotonic loading. In the experiment, the compressive strength decreases, and the ultimate strain increases as the ratio of side length increases. Furthermore, we proposed an evaluation formula for a rectangular cross-section concrete element reinforced with CFS. The proposed formula corresponds well to the experimental results.

Abstract: The specimens (980 MPa-grade dual phase steel sheets) were stretched until the pre-defined strain was obtained. Then the specimens were held at the pre-defined strain and measured the change of stress durng holding. We investigated the effects of strain rate and strain at the starting time of holding and whether the stress change during holding could be described by Krempl model. The following results were obtained. First, the stress drop increased with increase of strain rate and the holding time. On the other hand, the stress drop was not affected by strain change at the starting time of holding. Second, initial stress relaxation rate increased with increase of strain rate. However, this strain rate dependency to stress relaxation rate diminished as the holding time became long enough roughly more than 100 s. Third, the stress change during holding obtained by Krempl model accurately agreed with experimental result. It was found that the stress change during holding could be well described by using Krempl model. This suggests that dislocation moves viscously. In addition, the strain rate dependency on stress change during holding could be described by change of the parameter A.

Abstract: It is given stress-strain relationships of concrete and reinforcing deformation under high temperatures. These graphs show material features of deformation, look compact and require least defined parameters.

Abstract: The post-peak stress strain relationship expression of intact rock cannot well reflect post peak properties of rock masses with joint, in order to obtain post peak stress-strain relationship suitable for rock masses with joint, based on the test data, based on the Kulun strength criterion, analysis evolution of post peak strength parameters of rock masses with joint. According to rock masses with joint under different confining pressure and fracture dip at different post peak behavior, the post peak stress-strain relationship is simplified as new kind type, regarding maximum principal strain as strain softening parameter, on the assumption cohesion and internal friction angle are the piecewise linear functions of maximum principal strain, the method of solving express of new post-peak stress-strain relationship of rock masses with joint is obtained.

Abstract: Compressive experiments on mortar-free grouted concrete masonry composed with hollow blocks were studies in this essay. Characteristics of compressive stress-strain curve were analyzed by utilizing test data of 15 specimens with 100% filling rate of grouted concrete. Further more, elastic modulus formula was proposed according to results of previous and present work.

Abstract: Structural study of the soil is an important research content of soil mechanics. Based on the previous research results of soil structure, this paper puts forward the Gunary Model as a completely new form to describe the stress-strain relationship of soil, to discuss the method to determine soil strain considering structural parameter under the new model, to give the relevant function of the stress controlling structural parameter with stress. The results show that the Gunary Model is applicable to characterize the stress-strain relationship of soil, the parameter controls the fitting accuracy and decides the curve shape; by using the stress-strain expression of the Gunary Model, this paper finds the calculated value of stress controlling structural parameter and stress meets the two-parameter linear reciprocal function form.

Abstract: The mechanical property of polyvinyl chloride (PVC) geomembrane was usually expressed using engineering stress-strain response in traditional uniaxial tension test. By failing to account for deformation of specimen during the test, the deviation of true stress and strain maybe caused from the test results. In this paper, the true stress-strain response of PVC geomembrane was investigated using uniaxial tension test. The photographic analysis method was used to measure axial and lateral true strain of specimen. The Poissons ratio and true stress were also acquired based on measured true strain in the test. Then the true stress-strain relationship was obtained from the test results. By comparing with the engineering stress-strain results expressed by traditional method, it can be found that the engineering stress-strain result is unreasonable. The engineering stress-strain expression easily leads to the underestimation of the true stress.

Abstract: Tailor-welded tubes are widespread in aircraft and automotive industries due to their advantages of low cost, reduction in part weight and flexibility in mass production. It is necessary to obtain the stress-strain relationship of tailor-welded tubes to study deformation behaviors of tubes and simulate deformation tests of tubes. Then a method via digital image correlation (DIC) method based on uniaxial tensile test (UTT) is proposed in this paper to establish stress-strain relationship of tailor-welded tubes. Material parameters of tailor-welded tubes obtained from three methods, i.e. the method based on UTT, the iso-strain method based on a rule of mixtures and the proposed method, were compared in this paper. To assess the accuracy of material parameters obtained from these three methods, UTTs were simulated, and load-displacement curves and maximal loads obtained from simulations were compared with those obtained from UTTs. In simulations of UTTs, finite element models of specimens of sole parent metal and mixed specimens were established, respectively. The results show that: When HAZ included in the specimen has large proportion of the specimen, the proposed method is more reliable than the iso-strain method based on a rule of mixtures on determining the material parameters of the weld; load-displacement curve and maximal load obtained from the proposed method are more close to those obtained from UTT than those obtained from the method based on UTT.

Abstract: It is well established that lateral confinement of concrete enhances its axial strength and deformability. It is often assumed that, at a same level of confining pressure, the axial compressive stress and strain of fiber reinforced polymer (FRP)-confined concrete at a given lateral strain are the same as those in concrete actively confined concrete. To assess the validity of this assumption, an experimental program relating both types of confinement systems was conducted. 25 FRP-confined and actively confined high-strength concrete (HSC) specimens cast from a same batch of concrete were tested under axial compression. The axial stress-strain and lateral strain-axial strain curves obtained from the two different confinement systems were assessed. The results indicate that, at a given axial strain, lateral strains of actively confined and FRP-confined concretes correspond, when they are subjected to the same lateral confining pressure. However, it is observed that, at these points of intersections on axial strain-lateral strain curves, FRP-confined concrete exhibits a lower axial stress than the actively confined concrete, indicating that the aforementioned assumption is not accurate. The test results indicate that the difference in the axial stresses of FRP-confined and actively confined HSC becomes more significant with an increase in the level of confining pressure.

Abstract: It is now well understood that the hoop rupture strain of fiber reinforced polymer (FRP) jackets confining concrete is often lower than the ultimate tensile strain of the component fibers. A number of reasons for the lower hoop rupture strains in FRP have been identified; however, the relationships between the material properties of FRP-confined concrete and hoop ruptures strains are yet to be established. This paper presents the results of an experimental study into the factors influencing the hoop strain efficiency of FRP jackets. 24 FRP-confined concrete specimens were tested under axial compression. The results indicate that the hoop rupture strains of FRP jackets decrease with either an increase in the strength of the unconfined concrete or the elastic modulus of the fiber material. These observations were verified by additional results from a large FRP-confined concrete test database assembled from the published literature.