Uniaxial Strain Data Research Articles

Parameter determination of Johnson–Holmquist–Cook constitutive model and calibration for Indiana Limestone

In this study, a comprehensive parameter determination procedure for the Johnson–Holmquist–Cook (JHC) constitutive model is introduced, including calibration and validation processes for Indiana Limestone rocks. The procedure is conducted utilizing the existing physical and mechanical properties of Indiana Limestone. To obtain an accurate set of parameters for the JHC model for Indiana Limestone, an extensive dataset comprising mechanical and physical properties of Indiana Limestone rocks was initially compiled. The static mechanical tests incorporated uniaxial compression, triaxial compression, direct tensile, and uniaxial strain data, while the dynamic mechanical test data was primarily derived from the Split Hopkinson Pressure Bar experiments. Subsequently, the JHC constitutive model parameters were determined using existing literature data, employing statistical analysis, theoretical derivation, and numerical back analysis techniques. One of the damage parameters was determined through numerical post-peak behavior calibration of triaxial compression strength test results on experimental data. Finally, the accuracy of the determined parameters was validated by comparing the numerical and experimental results of both static and dynamic tests. This study effectively addresses the challenges associated with the numerical method using the JHC material model, such as the complex parameter determination process and the costly required tests, thereby preserving the efficiency and applicability of the numerical method.

Full-Field Strain Reconstruction Using Uniaxial Strain Measurements: Application to Damage Detection

This work investigates the inverse problem of reconstructing the continuous displacement field of a structure using a spatially distributed set of discrete uniaxial strain data. The proposed technique is based on the inverse Finite Element Method (iFEM), which has been demonstrated to be suitable for full-field displacement, and subsequently strain, reconstruction in beam and plate structures using discrete or continuous surface strain measurements. The iFEM uses a variationally based approach to displacement reconstruction, where an error functional is discretized using a set of finite elements. The effects of position and orientation of uniaxial strain measurements on the iFEM results are investigated, and the use of certain strain smoothing strategies for improving reconstruction accuracy is discussed. Reconstruction performance using uniaxial strain data is examined numerically using the problem of a thin plate with an internal crack. The results obtained highlight that strain field reconstruction using the proposed strategy can provide useful information regarding the presence, position, and orientation of damage on the plate.

Three dimensional shape and stress monitoring of bulk carriers based on iFEM methodology

Over the last few years, inverse finite element method (iFEM) is shown to be one of the most robust and general algorithms for the purpose of shape and stress sensing. This study concerns the application of iFEM methodology to a capsize bulk carrier and investigates an appropriate sensor placement configuration for better structural health monitoring of the vessel. The measured uniaxial strain data, e.g. the ones collected from fiber Bragg grating (FBG) sensors, are processed by the developed iFEM framework. For this purpose, hydrodynamic and finite element analyses are performed to generate simulated FBG sensor-strains data for the bulk carrier floating in head sea wave condition. Up to ten percent white noise is added on the numerical strain data to represent experimental strain measurements collected from real FBG sensors. The influence of FBG sensor locations as well as noise level in the strain measurements are examined versus the solution accuracy. Based on the displacement and stress comparison between iFEM and the reference solutions, it was observed that a sparse deployment of FBG sensors is sufficient to predict accurate bending response of the vessel. Hence, practical applicability of iFEM technology together with FBG sensors is demonstrated for the bulk carriers.

Invariant temperature and field strain functions for Nb 3Sn composite superconductors

The observed strain dependence of Nb 3Sn over an extended range of applied strain requires revision of the functions used previously to represent that strain dependence. The concept and various definitions of the strain function for the upper critical field and the critical temperature are reviewed. An invariant strain function for the critical temperature is derived from the strain energy potential of the general invariant strain analysis. The invariant strain function is applied to a study of uniaxial longitudinal applied strain on wire and tape conductors. Uniaxial forms of the general strain function are derived, and parameter values of the strain function are determined from a fit of the uniaxial forms to published uniaxial strain data for the critical temperature. The concept of precompression is examined in the context of the strain function. The invariant strain function, as an analytic function, is compared with numerical calculations of the general invariant strain analysis for longitudinal and transverse applied strain. The correspondence between the strain dependence of the critical temperature and the upper critical field is discussed, and a form of the invariant strain function for the upper critical field is presented.

Plane shock wave studies of Westerly Granite and Nugget sandstone

Plane shock wave experiments were performed by using a light-gas gun on dry and water-saturated Westerly granite and dry Nugget sandstone. Changes in the slopes of the shock velocity versus particle velocity curves at 2–3 GPa and 1–2 GPa for dry granite and for dry sandstone, respectively, are attributed to the onset of pore collapse. However, there is little apparent loss of shear strength in either dry rock over the stress range of the experiments (i.e. 9.3 GPa in Westerly granite and 9.2 GPa in Nugget sandstone). Agreement between the shock wave data and quasistatic, uniaxial strain data for the dry rocks implies the absence of rate-dependence in uniaxial strain. The shock data on saturated granite agree well with those for dry granite, thus suggesting there was no loss in shear strength as a result of pore pressure buildup.

Structure of transition-metal—oxygen-vacancy pair centers

The microscopic structure of the ${\mathrm{Fe}}^{3+}$-${V}_{\mathrm{O}}$ and ${\mathrm{Mn}}^{2+}$-${V}_{\mathrm{O}}$ pair centers has been considered using the Newman superposition model. This model yields the EPR parameter ${b}_{2}^{0}$ as a function of transition-metal-ion-oxygen distance $d$ and position. It is found, for the oxide perovskites, that the transition-metal ion moves by a distance $\ensuremath{\Delta}=0.1$ $d=0.2$ \AA{} towards the vacancy ${V}_{\mathrm{O}}$. The four lateral oxygens move against the metal ion by 4% or 0.08 \AA{}. This is in agreement with the reduction of the metal ionic radius due to the five-fold coordination. The intrinsic two-center parameter ${\overline{b}}_{2}$ needed in the Newman model is based on the uniaxial strain data of MgO and SrTi${\mathrm{O}}_{3}$, as well as on the measured spin-Hamiltonian parameter ${b}_{2}^{0}$ in the tetragonal phase of SrTi${\mathrm{O}}_{3}$. The ${\overline{b}}_{2}$ parameters obtained also provide information on other centers reported in oxide and fluoride compounds.

Strain rate dependence in dolomite inferred from impact and static compression studies

Plate impact techniques and laser interferometry instrumentation were used to obtain continuous one-dimensional compression wave data through states of loading and unloading on Blair dolomite in the stress range of 0 to 6.5 GPa. These data are used to infer the dynamic stress--strain response. Both the character of the wave propagation and a comparison with quasi-static uniaxial strain data obtained by other workers suggest substantial strain rate dependence in this rock. The dynamic yield stress of 2.5 GPa determined from the wave propagation data was approximately a factor of 10 higher than that observed in the quasi-static data. Wave propagation below 2.5 GPa is suggestive of viscoelastic response, and a nonlinear Maxwell constitutive equation fitted to these data provides a characteristic relaxation time of 0.01 ..mu..s. Comparison of dynamic and quasi-static loading data suggests that the large difference in observed yield stress could be the result of a transition from failure by brittle fracture to failure by intracrystalline plastic flow.

Stress relaxation, creep, and uniaxial strain: General and special features

Papers devoted to the development of methods of describing the behavior of materials during creep and stress relaxation in terms of uniaxial strain data are usually based on the idea of the existence of a mechanical equation of state, i.e., an equation relating deformation or rate of deformation, temperature, stress, and time for such processes. The idea of a mechanical equation of state was first put forward by Nadai [1] and Zener and Holloman [2]. Holloman [3] has reported some experimental evidence for the existence of such an equation of state. However, Orowan [4], Dorn et al. [5], and Johnson et al. [6] have obtained data which are not in agreement with this idea. Freudenthal [7] has considered the physical basis of these processes and their mathematical description, and has not rejected the basic possibility of conversion of the data of one type of test into another. He ascribes the various difficulties in this area to insufficient knowledge about the nature of these processes. Guiu and Pratt [8] have come to the same conclusion and have noted the complexity of the processes taking place in the material under test.