Experimental Techniques最新文献

Substructuring is a term used to describe the estimation of the dynamics of a coupled system assembly when only the dynamics of each uncoupled component is available. Existing approaches allow for the coupling of physical-to-physical models, physical-to-modal models, modal-to-modal models referred to as Component Mode Synthesis (CMS), and impedance-to-impedance models referred to as Frequency Based Substructuring (FBS). Often times, the component information may not be just modal data for both components or just FRF data for both components so that modal substructuring or FRF substructuring can be performed. In these cases, the component data needs to be converted from either modal data or FRF data to match the data of the other component. A method for directly coupling impedance- and modal-based components has not yet been addressed. A proposed Impedance to Modal Substructuring (IMS) approach addresses this situation by writing the equations in a form that allows the user to directly utilize modal data for one component and FRF data for the other component, offering more flexibility in coupling different component data sets. While intended to be used with experimental data, this approach may also implement analytical components. In this work, an approach was developed to allow for the direct coupling of impedance and modal models without the need for the user to convert component data type. The IMS approach derived in this work was validated using analytical and experimental data with various models.

The design and development of Indium Tin Oxide (ITO) thin film based piezoresistive pressure sensor is presented in this paper. ITO (90:10) nanoparticles were synthesized by green combustion method using indium and tin as precursors and, carica papaya seed extract as fuel. ITO (90:10) thin film piezoresistors were deposited using synthesized nanoparticles on AlN coated circular steel (SS 304) diaphragm using E-beam evaporation technique. Diaphragm models of different thickness (0.75, 1 and 1.25 mm) were created using ANSYS finite element analysis in order to determine the maximum stress and deflection region for applied pressure of 1 to 10 bar. ANSYS results exhibited that maximum stress and deflection occurred at the center and circumference of diaphragm. ITO thin film piezoresistors were deposited at these regions using mechanical mask. TiW metal contact was established to these ITO thin film piezoresistors using DC sputtering method. ITO thin film piezoresistive pressure sensor with TiW contact connected in Wheatstone full bridge configuration was calibrated and tested for 50 pressure cycles by applying 2 V DC supply. Sensitivity (S) of the developed ITO thin film pressure sensor was obtained as 0.686, 0.566 and 0.495 mV/bar for diaphragm thickness of 0.75, 1, and 1.25 mm pressure sensors respectively. The non-linearity (NLi) in the output response of the pressure sensors was found to be 9.14, 9.82 and 11.27% for diaphragm thickness of 0.75, 1, and 1.25 mm respectively. Hysteresis errors were found to be 0.0344, 0.0525 and 0.054 for diaphragm thickness of 0.75, 1, and 1.25 mm respectively.

A thermomechanical finite element (FE) model was used to examine the effects of resistance spot welding (RSW) current intensity, time, and electrode force on the distribution of temperatures and the size of nuggets of IN-625 superalloy sheets. In order to evaluate and optimize the mechanical properties of RSW welded IN-625 alloy, a procedure was developed based on simulation results. A taguchi L9 experimental design was used to study the mechanical properties of welded samples as a function of peak load, failure mode, and energy. According to the findings, joint fracture modes and strength are significantly influenced by process parameters. Consequently, welding current, electrode force, and welding time all had significant impacts on the shear strength of IN-625 Alloy spot welding joints, with impacts of 62.05%, 24.06%, and 12.84%, respectively.

Hybrid simulation is an innovative method that combines an analysis model of a structural system with physical tests of one or more substructures. The analysis model is typically a finite element analysis (FEA) model that outputs displacements applied to the physical substructure using a control system operated in displacement control. For stiff specimens, the displacement commands can be so small that the control system has difficulty imposing the command displacements accurately. To do hybrid simulation with a stiff specimen, force control is desirable. Cascade control, which features two layers of closed loop control, is proposed to address this issue. The inner control loop has force control mode that provides accurate control for hybrid tests with stiff specimens. The outer control loop is in displacement control mode for accepting displacement commands from an FEA model. The effectiveness of the cascade control method in conducting hybrid simulation of stiff test specimens was evaluated with three sets of tests. For each set of tests, the results of both cascade control and displacement control methods were compared. The three test cases covered a wide range of variation from specimen size, test equipment, model type (2-D vs. 3-D), experimental element type (beam-column vs. truss), and test speed (slowdown 10 times in Test Case 1 and 2 versus 100 times in Test Case 3). In all cases, cascade control proved to be an effective method for conducting hybrid simulation with a stiff specimen.

Artificial muscles actuated by negative pressure offer significant benefits over those driven by positive pressure, such as high contraction ratios and improved safety, making them a promising option for various applications. This paper studies the contraction force characteristic of a bellows-like artificial muscle actuated by negative pressure. Initially, the structure, fabrication, and working principle of the artificial muscle were introduced. Subsequently, based on the force balance method, the contraction force was decomposed as the forces acted by the difference value of the inner and the outer pressures on the end plate, and the tension force derived from the adjacent contraction unit. To reduce complexity, the contraction process was divided into three phases according to the distinct contact conditions of the contraction units: uncontacted, locally contacted, and fully contacted with crests. The deformations of the contraction units in each phase were analyzed, and the corresponding contraction forces were derived. An experiment platform was constructed to test the force by changing the dimension parameters and pressure, obtaining the output force data during isobaric contraction. Finally, a comparison of the experimental and calculated results substantiated the aptness of the theorem model.

The efficient characterization of material properties of porous multi-phase sintered steels by instrumental indentation is still an open question. To the authors’ knowledge, so far only a characterization of single-phase porous sintered steel by nanoindenation has been reported in literature. This paper for the first time offers a study about the applicability of microindentation techniques for characterizing the matrix material in a multi-phase sintered steel. This preliminary study is motivated by the relatively wide availability of necessary equipment, and simplicity of material identification procedures.

Herein, a dual-phase ferrite/bainite Astaloy steel with 9% porosity is studied. Various commonly used methods for the reconstruction of stress–strain curves from microindentation data are considered, whereby both Vickers and spherical tips are used. In addition, some homogeneous solid materials are investigated to better asses the performance of applied identification procedures. Two approaches for the mesoscale identification of the considered sintered steel are attempted. The first one is based on the identification of individual material phases, while in the other one the homogenization of the metallic matrix is adopted. To assess the reliability of obtained parameters, the direct numerical simulation of representative volume elements of realistic steel microstructure subjected to uniaxial tension is conducted. Numerical results are compared with the data from the macroscopic uniaxial tensile test.

The obtained results indicate that microindentation is adequate for the identification of elastic properties of individual material phases, but results for local plastic parameters are largely inconclusive and a further analysis is needed, focusing on applying smaller forces and investigating the influence of pores on identification results. Nevertheless, it seems that macroscopic stress–strain curves could be captured more accurately by the methodology based on the matrix homogenization if relatively large indentation forces are applied.

An essential consideration for metal-polymer applications is that the sound joining of these materials is challenging due to a significant surface energy differential in different structural characteristics between polymer and metal. However, the joining methods have some drawbacks, such as low-reliability joints, long curing time, stress concentration, and polymer degradation. A new novel metal-polymer hybrid joining technique is proposed in this work to overcome these issues and cost perspectives, manufacturing, and overcoming the problem of PVC degradation due to heat generation of other joining methods. In this study, we managed to join PVC to AA5053 sheets using a cold joining technique based on extruding PVC through a conical hole of an aluminum specimen using a punching tool. Experiments consisted of three parameters (the hole diameter, plunging depth, and radius of the punch), with four levels for each parameter. The experiments were designed, and mechanical characterizations of the joints were optimized using the design of the experiment's method. The hole diameter was the effective parameter on the mechanical characterizations and dimensions of the extruded PVC. Increasing the diameter of the AA5053 sheet increased the maximum diameter of the extruded PVC, shear force, and pull-out force of the joints and decreased the shear stress of the joints. We obtained a maximum shear strength of 106.15 MPa, which is ~3 times higher than the tensile strength of PVC (37 MPa).