An aluminium AD-3 has been anodized under four different conditions, namely at low temperature (?5℃), room temperature (25℃), with and without sealing the anodized coating in boiling distilled water. The solution us...An aluminium AD-3 has been anodized under four different conditions, namely at low temperature (?5℃), room temperature (25℃), with and without sealing the anodized coating in boiling distilled water. The solution used for formation of alumina layer in all cases was an electrolyte containing 180 g/l sulphuric acid at a constant forming voltage (voltastatic anodizing). In order to assess the mechanical properties of the obtained anodic alumina layers a series of nanoindentation tests was performed employing different indentation procedures. The two mechanical characteristics of the alumina films, the indentation hardness (HIT) and the indentation modulus (EIT), were determined by means of the instrumented indentation and the Oliver & Pharr approximation method. All measurements were done on Agilent G200 Nanoindenter fitted with a diamond Berkovich type tip. Time dependent effects were investigated by tests with different peak hold time and different loading rate. The change of the mechanical properties with indentation depth was also examined. The effect of the working temperature during the growth of the alumina layers and the influence of the pore sealing on the mechanical properties are evaluated via comparison of the average load-displacement curves. The role of the temperature of the electrolyte and the sealing process during the formation of the alumina films, with respect to possible changes of their chemical composition and structure, are discussed in order to explain the observed differences in the measured load-displacement curves and the determined HIT and EIT.展开更多
When performing shallow tunnel construction,settlements on the ground surface often cannot be prevented.Anticipating these sur-face displacements is only possible with profound knowledge of the constitutive parameters...When performing shallow tunnel construction,settlements on the ground surface often cannot be prevented.Anticipating these sur-face displacements is only possible with profound knowledge of the constitutive parameters of the surrounding soil.Performing inverse analysis on the basis of in situ settlement data is an effcient method for obtaining such information.However,during this process,con-sidering which measurement arrangement can provide the most reliable results is generally neglected.This aspect is addressed in this study by applying the so-called“optimal experimental design”to the mechanized tunnelingfield.A global sensitivity analysis(GSA)isfirstly performed to determine the most relevant model parameters to be identified via back analysis,by employing the considered numerical model and experimental data.Furthermore,the GSA results are utilized to determine where and when measurements should be performed to minimize uncertainty in the identified constitutive parameters.The optimal experimental design(OED)concept is fur-ther applied to evaluate the observation set-up effciency for damage mitigation measures within a representative synthetic example of a tunneling project passing beneath an existing building.Parameter identification based on synthetic noisy experiments is performed to validate the presented method for optimal experimental design.Thus,the soil stiffness and strength parameters are identified according to both an intuitive and the elaborated method,employing the proposed OED strategy and experimental designs,making it possible to assess the feasibility of the OED results.展开更多
文摘An aluminium AD-3 has been anodized under four different conditions, namely at low temperature (?5℃), room temperature (25℃), with and without sealing the anodized coating in boiling distilled water. The solution used for formation of alumina layer in all cases was an electrolyte containing 180 g/l sulphuric acid at a constant forming voltage (voltastatic anodizing). In order to assess the mechanical properties of the obtained anodic alumina layers a series of nanoindentation tests was performed employing different indentation procedures. The two mechanical characteristics of the alumina films, the indentation hardness (HIT) and the indentation modulus (EIT), were determined by means of the instrumented indentation and the Oliver & Pharr approximation method. All measurements were done on Agilent G200 Nanoindenter fitted with a diamond Berkovich type tip. Time dependent effects were investigated by tests with different peak hold time and different loading rate. The change of the mechanical properties with indentation depth was also examined. The effect of the working temperature during the growth of the alumina layers and the influence of the pore sealing on the mechanical properties are evaluated via comparison of the average load-displacement curves. The role of the temperature of the electrolyte and the sealing process during the formation of the alumina films, with respect to possible changes of their chemical composition and structure, are discussed in order to explain the observed differences in the measured load-displacement curves and the determined HIT and EIT.
文摘When performing shallow tunnel construction,settlements on the ground surface often cannot be prevented.Anticipating these sur-face displacements is only possible with profound knowledge of the constitutive parameters of the surrounding soil.Performing inverse analysis on the basis of in situ settlement data is an effcient method for obtaining such information.However,during this process,con-sidering which measurement arrangement can provide the most reliable results is generally neglected.This aspect is addressed in this study by applying the so-called“optimal experimental design”to the mechanized tunnelingfield.A global sensitivity analysis(GSA)isfirstly performed to determine the most relevant model parameters to be identified via back analysis,by employing the considered numerical model and experimental data.Furthermore,the GSA results are utilized to determine where and when measurements should be performed to minimize uncertainty in the identified constitutive parameters.The optimal experimental design(OED)concept is fur-ther applied to evaluate the observation set-up effciency for damage mitigation measures within a representative synthetic example of a tunneling project passing beneath an existing building.Parameter identification based on synthetic noisy experiments is performed to validate the presented method for optimal experimental design.Thus,the soil stiffness and strength parameters are identified according to both an intuitive and the elaborated method,employing the proposed OED strategy and experimental designs,making it possible to assess the feasibility of the OED results.
