In order to achieve the same origin three-dimensional （3D） strain measurement, one three-dimensional （3D） fiber Bragg grating （FBG） strain sensor is proposed in this paper. The metal structure of this sensor is ...In order to achieve the same origin three-dimensional （3D） strain measurement, one three-dimensional （3D） fiber Bragg grating （FBG） strain sensor is proposed in this paper. The metal structure of this sensor is composed by three elliptical tings with different geometrical parameters. All these elliptical tings make sure that this sensor achieves the same origin 3D strain detection and increases the strain measurement coefficient. A theory calculation model of this sensor is established. The finite element method is utilized to optimize this sensor and verify the correctness of the theory model. After sensor optimization, 1 mm is chosen as the radical thickness of this sensor based on taking high strain detection coefficient and structure strength into account. To further obtain detection characteristics of this sensor, the calibration experiment is carried out. Experimental data of FBG1 which is the core sensitive element of this sensor is chosen as the specimen to be analyzed by the least square method. When the wavelength of FBG1 is changed by external stress, wavelengths of FBG2 and FBG3 have just a little fluctuation maybe caused by the fiber demodulation instrument SM125. So sensitive elements （FBG1, FBG2, and FBG3） of this sensor have no crosstalk problem for three-dimensional detection. After data analysis, the measuring coefficient of FBG1 is 0.05 nm/N. Similarly, the coefficients of FBG2 and FBG3 are 0.045 nm/N and 0.39nm/N, respectively. All these data confirm that this sensor could achieve the same origin 3D strain measurement without the crosstalk problem and has certain practical applications.展开更多
ISO 10113:2020中提供了人工、半自动、全自动3种测量塑性应变比r值的方法。分别讨论了3种测量方法、不同测量设备以及试样类型对测量结果的影响。结果表明:采用人工、半自动、全自动方法测量的r值不存在显著差异,其中全自动方法的测量...ISO 10113:2020中提供了人工、半自动、全自动3种测量塑性应变比r值的方法。分别讨论了3种测量方法、不同测量设备以及试样类型对测量结果的影响。结果表明:采用人工、半自动、全自动方法测量的r值不存在显著差异,其中全自动方法的测量精度最高;激光非接触式引伸计与机械接触式引伸计测量的r值接近,但前者的精度更高;当采用JIS5试样进行r值测量时,应避免采用50mm标距,推荐采用20~30mm标距。同时对GB/T 5027—2016提出了修订建议。展开更多
Shear-box test with strain measurement was used to study time-dependent stress and strain of in-plane shear(Mode Ⅱ) fracture process of rock and to reveal the mechanism of Mode Ⅱ fracture.Numerical results show that...Shear-box test with strain measurement was used to study time-dependent stress and strain of in-plane shear(Mode Ⅱ) fracture process of rock and to reveal the mechanism of Mode Ⅱ fracture.Numerical results show that the maximum shear stress τmax at the crack tip is much larger than the maximum tensile stress σ1 and the ratio of τmax/σ1 is about 5,which favors Mode Ⅱ fracture of rock.Test results indicate that the strain-time curve comprises three stages:the linear deformation stage,the micro-cracking stage and the macroscopic crack propagation.The strain in the direction of the original notch plane is negative,due to restraining effect of compressive loading applied to the original notch plane.Both σ1 and τmax are increased as the load increases,but the slope of τmax is larger than that of σ1 and the value of τmax is always larger than that of σ1.Therefore,τmax reaches its limited value at peak load before σ1 and results in Mode Ⅱ fracture of rock.Shear-box(i.e.compression-shear) test becomes a potential standard method for achieving the true Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock.展开更多
文摘In order to achieve the same origin three-dimensional （3D） strain measurement, one three-dimensional （3D） fiber Bragg grating （FBG） strain sensor is proposed in this paper. The metal structure of this sensor is composed by three elliptical tings with different geometrical parameters. All these elliptical tings make sure that this sensor achieves the same origin 3D strain detection and increases the strain measurement coefficient. A theory calculation model of this sensor is established. The finite element method is utilized to optimize this sensor and verify the correctness of the theory model. After sensor optimization, 1 mm is chosen as the radical thickness of this sensor based on taking high strain detection coefficient and structure strength into account. To further obtain detection characteristics of this sensor, the calibration experiment is carried out. Experimental data of FBG1 which is the core sensitive element of this sensor is chosen as the specimen to be analyzed by the least square method. When the wavelength of FBG1 is changed by external stress, wavelengths of FBG2 and FBG3 have just a little fluctuation maybe caused by the fiber demodulation instrument SM125. So sensitive elements （FBG1, FBG2, and FBG3） of this sensor have no crosstalk problem for three-dimensional detection. After data analysis, the measuring coefficient of FBG1 is 0.05 nm/N. Similarly, the coefficients of FBG2 and FBG3 are 0.045 nm/N and 0.39nm/N, respectively. All these data confirm that this sensor could achieve the same origin 3D strain measurement without the crosstalk problem and has certain practical applications.
基金Project(50374073) supported by the National Natural Science Foundation of ChinaProject(1343-77239) supported by the GraduaEducation Innovation Project of Central South University,China
文摘Shear-box test with strain measurement was used to study time-dependent stress and strain of in-plane shear(Mode Ⅱ) fracture process of rock and to reveal the mechanism of Mode Ⅱ fracture.Numerical results show that the maximum shear stress τmax at the crack tip is much larger than the maximum tensile stress σ1 and the ratio of τmax/σ1 is about 5,which favors Mode Ⅱ fracture of rock.Test results indicate that the strain-time curve comprises three stages:the linear deformation stage,the micro-cracking stage and the macroscopic crack propagation.The strain in the direction of the original notch plane is negative,due to restraining effect of compressive loading applied to the original notch plane.Both σ1 and τmax are increased as the load increases,but the slope of τmax is larger than that of σ1 and the value of τmax is always larger than that of σ1.Therefore,τmax reaches its limited value at peak load before σ1 and results in Mode Ⅱ fracture of rock.Shear-box(i.e.compression-shear) test becomes a potential standard method for achieving the true Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock.
