Experimental Techniques最新文献

Background

The implanted non-vascular stent is prone to fatigue fracture due to the periodic cyclic load caused by long-term physiological motion in the non-vascular lumen.

Objective

To effectively study and predict the fatigue performance of non-vascular stents, an experimental setup was designed to simulate and conduct fatigue performance tests on non-vascular stents under various loads. This design simplified the periodic cyclic loads generated within non-vascular lumens, in accordance with the physiological motion patterns of non-vascular lumens, into pulsatile loads.

Methods

To meet the requirements of different stents and various fluctuating load conditions during testing, the relationship between test conditions and the fatigue load of the stent was studied based on Fluent.

Results

A fatigue test device with a special load module was built and used to complete the fatigue performance test of a group of esophageal stents. It can be found that the experimental device can satisfy the control and application of the fatigue load of the stent, and can effectively realize the testing requirements of the fatigue performance of the stent.

Conclusion

In this paper, a non-vascular stent fatigue in vitro test device that can simulate the fluctuating load of a non-vascular lumen is designed. The results of flow field simulation, fatigue simulation, and actual fatigue test show that the device can meet the needs of fatigue test and has good versatility and operability.

This study investigated the stress–strain behavior of seamless pipes in the hoop direction using the ring expansion test, which is a non-standardized mechanical testing technique used for evaluating the mechanical properties of round tubes. However, this technique has limitations, such as unidentified specimen geometry, strain measurement, and the estimation of friction coefficients. The study employed experimental, numerical, and analytical methodologies to address these limitations and throughout the study, a novel hoop stress correlation factor (K) was identified to be multiplied by the hoop stress derived equation for reduced section ring specimens. The experimental strain was measured using a newly derived analytical equation, and a mathematical predictive model was developed to estimate the K-factor using the Design of Experiment (DoE) and Design-Expert statistical software. The study concluded that the ring expansion test is a promising technique for evaluating the mechanical properties of seamless pipes similar to the unified axial tensile stress–strain behavior. However, future research is needed to estimate the hoop stress correlation value (K) for all ring geometries. The study's finding of the novel hoop stress correlation factor (K) in the case of a reduced section ring specimen is particularly noteworthy, as it addresses a significant research gap in the field.

Microelectronics packages play a vital role in not only interconnecting the electronic signals from the die to the printed circuit board (PCB), but also in protecting the chips during the manufacturing process and their subsequent service lives. Epoxy molding compound (EMC) is widely used in electronic packaging due to its superior processing capability and low circuit signal delay. However, interfacial delamination is a common problem in encapsulated silicon devices, particularly at the interface between the copper leadframe (LF) pads and the EMC due to the weaker adhesion strength. Accordingly, the present study employs a double cantilever beam (DCB) experimental testing method and a numerical model based on the virtual crack closure technique (VCCT) to investigate the fracture behavior at the EMC/Cu LF interface in a quad flat no leads (QFN) package. The experiments are performed on an MTS-Acumen microforce tester equipped with a load unit capable of applying a force of 0.01 to 1250 N with a displacement resolution of 0.1 μm. The DCB specimens are prepared with a pre-crack length of 12 mm. The validity of the simulation model is confirmed by comparing the predicted values of the critical strain energy release rate (SERR, G_c) between the EMC and the copper LF pads with the experimental observations. In general, the results show that the G_c value provides a useful parameter for evaluating the delamination risk of encapsulated microelectronics packages and assessing the reliability of alternative package architectures.

Implementing smart materials as an actuator in fabricating micro-positioning systems has become pervasive in recent years. However, the application of Shape Memory Alloy (SMA) smart materials is limited due to its complex nonlinear mechanical behavior, such as asymmetric hysteresis and saturation characteristics. One of the most potent experimental-based methods of modeling these nonlinearities is the Generalized Prandtl-Ishlinskii (GPI) model. Unlike similar methods such as the Preisach model, this model is analytically invertible. This study aims to develop a micro-positioning stage and identify an experimental-based model describing the system response. The model structure is composed of two cascade sub-models. In the first sub-model, which models the actuator thermal behavior, the parameters of a linear dynamic model are identified. This sub-model predicts the actuator temperature given the electrical current. The second sub-model estimates the phase transformation and consequently the actuator displacement as a function of temperature. The GPI structure has been used for constructing the Wiener sub-model. The experimental and numerical results showed that the proposed black box model can accurately describe the system behavior, although identifying a comprehensive model to adequately describe the SMA actuator is a great challenge.

The boundary performance of direct-acting pressure valves (DAPV) is significantly impacted by surging in small opening situations. This paper illustrates the causes of vibration of DAPVs under small opening conditions from the viewpoints of statics and dynamics. This paper studies a pressure valve using several techniques. These include studying the structural dynamics of the pressure valve using experimental and modal analysis methods, simulating the pressure valve vibration process using flow-solid-control coupling simulation methods, and studying the internal jet characteristics of the pressure valve using non-constant flow field simulation analysis methods. Based on the conclusions drawn from the above methods, several possible effective vibration damping methods are proposed to improve the performance of DAPVs under low flow conditions.

The present study focused on the machinability of Ti-3Al-2.5 V for wire-electrical discharge machining (WEDM) using "BroncoCut-X wire" (zinc-coated copper wire). The machining characteristics have been evaluated by varying wire-tension (T_w), wire-speed (S_w), flushing-pressure (P_f), discharge current (I_d), and spark-on-time (S_on). The response characteristics associated with cutting-speed (Cs), kerf-width (KW), and surface roughness (RA) have been collected and analyzed using main-effect plots, scanning electron microscope (SEM), and analysis of variance (ANOVA). The maximum Cs and minimum KW and RA are obtained upto 8.90 mm/min, 3.34 µm and 0.2218 mm, respectively. Additionally, the novelty lies in the smart hybrid prediction tool considering the conflicting nature of responses are converted into single responses using Grey Relation Analysis (GRA) and Fuzzy Interference System (FIS) (Namely: Gray-Fuzzy Reasoning Grade (GFRG)). Furthermore, the optimal performance is calculated using Rao-algorithms (i.e., Rao1, Rao2, and Rao3). The obtained ideal machining condition is 16N wire-tension, 3 m/min wire-speed, 8 kg/mm² flushing-pressure, 21A discharge current, and 14 µs spark-on-time. The result has also been compared with the JAYA-algorithm and improved-grey wolf optimizer (I-GWO) to demonstrate the efficacy of the intended approach. The confirmation test has been conducted and obtained that the GFRG-based results are further improved by using a hybrid GFRG-based Rao-algorithm of 9.55%, 2.36%, and 7.99% as Cs, KW and RA, respectively. Furthermore, this study shows that the proposed multi-objective optimization method not only leads to more stable solutions but also to shorter run times and enhanced quality to support engineers in reducing the cost of item failures.

This paper represents an experimental and theoretical study of dynamic characteristics of coupling resonance between a deep-water riser (DR) and a floating platform. The super long DR used for transporting offshore oil & gas is a high dimensional nonlinear pipeline, and the complex characteristics of coupling response is clarified when the heave amplitude or frequency of the floating platform changes. By using the method of reverse combination of test data (RCTD), a fluid-structure coupling model of DR acted by internal fluid, wave flow and floating platform is constructed. Truncated equivalent method and frequency search method are both adopted to deal with the 1300 m DR during the experimental study on mechanism of coupling resonance. Results of the scaled model tests show that higher order resonance is easy to occur when the DR transports high-density fluid, and amplitude jump phenomenon appears in the resonance region at the DR top, which is closely related to the internal fluid transported. According to the transformation of similarity relationship, the results of scaled model test and numerical calculation are consistent, and equivalent truncation method is convenient to study the large-scale nonlinear DR structures.

The main purpose of this study is to exhibit failure prediction capability of polynomial-based yield functions with a basic damage model. For this purpose, a constitutive model considering anisotropic plasticity and ductile fracture was developed. In this model, anisotropic plastic behavior of dual phase steels, namely DP600 and DP800, was described by quadratic Hill48 and non-quadratic anisotropic homogeneous the fourth-order polynomial (HomPol4) stress potentials and the generalized plastic work criterion from ductile damage models was used for the prediction of fracture initiation. The model has been implemented into an implicit finite element (FE) code. The parameters of the constitutive model were calibrated with uniaxial tensile tests performed in different directions with respect to the rolling direction of the materials and anisotropic stress potentials were evaluated by comparison of the predicted in-plane variations of the plastic properties (yield stress ratios and Lankford coefficients), and yield locus contours with experimental data. The calibrated model was firstly applied to uniaxial tensile test and then to a hole expansion test to predict fracture. The stroke values at fracture, hole expansion ratios (HER) and fracture locations were investigated. Any significant difference between the anisotropic stress potentials was not observed in terms of HER predictions, however plastic work criterion in conjunction with HomPol4 function predicted the crack initiation locations accurately on the fractured samples. Afterward, the Lode parameter and stress triaxiality effects were investigated in fracture stroke prediction. Since the HomPol4 predictions of fracture initiation locations are accurate, the predicted HomPol4 results from the generalized plastic work criterion were compared with the modified Mohr-Coulomb ductile fracture model results. A significant improvement was observed in the fracture displacement predictions. However, it is seen that the failure location predictions of both models were the same. From these results, it can be concluded that the HomPol4 yield criterion has an effective potential to predict the failure locations even though with a basic damage model. In the current study, the out-of-plane anisotropy effect was assessed as well. To this end, Hill48’s parameter correlated with the out-of-plane shear components were adjusted. It was found that the out-of-plane anisotropy has a negligible effect on the predictions of HER and fracture initiation location.