Creep and cycle life in polypyrrole actuators

Conducting polymer actuators are of interest due to their low voltage operation, and their relatively high strains and forces. However, information is incomplete regarding the appropriate operating loads, the extent of creep and cycle life. We report cycle life and creep response in polypyrrole actuators operated in propylene carbonate. Polypyrrole films are found to extend passively by 2% after 100 min at 20 MPa, including about 1% elastic elongation. Results of creep tests at stresses of up to 60 MPa are presented, showing a non-linear and history dependent response at very high loads. The magnitude of the creep suggests that in situations where position control is desired under varying loads and at times of longer than tens of minutes that the polymer is best operated at loads of <20 MPa. Polypyrrole films passively cycled at a peak-to-peak amplitude of 8 MPa under an average load of 10 MPa for one million cycles show no apparent fatigue, suggesting that loading is not limiting cycle life. Films cycled by applying square wave potentials do show a drop in active strain. The strain amplitude decreases from 2% to 1% after 7000 cycles and an increased rate of creep is also observed during actuation. When the potential range is reduced such that the initial strain amplitude is 1.5% the strain drops to 1% after 32,000 cycles. The reduction in strain amplitude correlates with a decrease in charge transferred, suggesting degradation of the polymer is the cause of the loss in strain amplitude.     

A Hermite cubic collocation scheme for plane strain hydraulic fractures

We describe a novel cubic Hermite collocation scheme for the solution of the coupled integro-partial differential equations governing the propagation of a hydraulic fracture in a state of plane strain. Special blended cubic Hermite-power–law basis functions, with arbitrary index 0 < α < 1, are developed to treat the singular behavior of the solution that typically occurs at the tips of a hydraulic fracture. The implementation of blended infinite elements to model semi-infinite crack problems is also described. Explicit formulae for the integrated kernels associated with the cubic Hermite and blended basis functions are provided. The cubic Hermite collocation algorithm is used to solve a number of different test problems with two distinct propagation regimes and the results are shown to converge to published similarity and asymptotic solutions. The convergence rate of the cubic Hermite scheme is determined by the order of accuracy of the tip asymptotic expansion as well as the O(h⁴) error due to the Hermite cubic interpolation. The errors due to these two approximations need to be matched in order to achieve optimal convergence. Backward Euler time-stepping yields a robust algorithm that, along with geometric increments in the time-step, can be used to explore the transition between propagation regimes over many orders of magnitude in time.     

Improved digital photogrammetry technique for crack monitoring

Inspections to evaluate the safety, durability, and service life of aging infrastructure play an important role in determining the countermeasures that need to be taken, such as reinforcement, repair, and reconstruction. In infrastructure containing concrete, such as bridges and tunnels, crack widths and patterns on surfaces are two of the most important signs used to estimate durability. Current conventional techniques used for this purpose suffer from challenges such as tediousness, subjectivity, and high cost. Consequently, a new measurement technique that overcomes these challenges while measuring crack displacement with high accuracy and precision in aging civil engineering structures is needed. In this paper, we proposed a technique for measuring crack displacement using a digital camera image. In the proposed technique, reflective targets are established around both sides of a crack as gauges, and subsequent digital camera images of the targets are subjected to image processing to determine the displacements of the targets. These displacements can be measured using images captured from any arbitrary camera position. The results of experiments conducted to verify the efficacy of the proposed method show that crack displacements of less than 0.10 mm can be measured with high accuracy and precision using digital images captured at a distance of 10.0 m from the target, while less than 0.20 mm changes in the tensile displacement of the crack can be measured from an image captured at 25.0 m from the crack. Measurement results obtained from a tunnel are also presented to show that cracks in the walls of an actual tunnel can be identified through simple measurements. These measurements, taken over a period of one year, indicate that the tendency of crack displacement and slide movements are in close agreement.     

An intelligent strategy for checking the annual inspection status of motorcycles based on license plate recognition

License plate recognition techniques have been successfully applied to the management of stolen cars, management of parking lots and traffic flow control. This study proposes a license plate based strategy for checking the annual inspection status of motorcycles from images taken along the roadside and at designated inspection stations. Both a UMPC (Ultra Mobile Personal Computer) with a web camera and a desktop PC are used as hardware platforms. The license plate locations in images are identified by means of integrated horizontal and vertical projections that are scanned using a search window. Moreover, a character recovery method is exploited to enhance the success rate. Character recognition is achieved using both a back propagation artificial neural network and feature matching. The identified license plate can then be compared with entries in a database to check the inspection status of the motorcycle. Experiments yield a recognition rate of 95.7% and 93.9% based on roadside and inspection station test images, respectively. It takes less than 1 s on a UMPC (Celeron 900 MHz with 256 MB memory) and about 293 ms on a PC (Intel Pentium 4 3.0 GHz with 1 GB memory) to correctly recognize a license plate. Challenges associated with recognizing license plates from roadside and designated inspection stations images are also discussed.     

基于半解析模型的涡流传感器优化设计与实验研究

针对飞机金属螺栓孔连接结构疲劳裂纹的特点与实时监测的需求,提出了一种基于柔性平面的涡流阵列传感器,设计了疲劳裂纹扩展实时监测方案,构建了传感器损伤监测半解析模型,搭建了基于涡流阵列传感器的疲劳裂纹扩展实时监测平台。通过对涡流阵列传感器的仿真和基于涡流阵列传感器的疲劳裂纹扩展实验研究,确定了传感器的监测灵敏度,优化了传感器的特征参数。研究结果表明：传感器基材层阻碍了感应线圈与激励线圈的耦合,基材层应尽量薄。当涡流阵列传感器导电层厚度为0．12—0．18mm,激励线圈的最优宽度为0．8min,感应线圈的最佳厚度为0．5mm时,传感器的损伤监测灵敏度最高。     

Development of a novel micromirror based on surface micromaching technology

A novel 3 × 3 micromirror array is designed and successfully fabricated with multi-layer silicon surface micromaching technology. It is composed of bottom electrode, support part and mirror plate, in which a T type beam structure is used to support the mirror plate. It can provide mirror with the vertical movement and the rotation about two horizontal axes, thus enabling phase modulation and amplitude modulation for the incident light. The test results show that the maximum deflection length along the vertical direction of the mirror plate is 2 μm, while the rotation angle about X- and Y-axis are ±2.3° and ±1.45°, respectively.     

A MEMS-based tracking milli-mirror for high-density optical disk drives

We present a new MEMS-based milli-mirror for precise tracking in high-density optical disk drives (ODDs). The device consists of a torsionally suspended mirror plate, one pair of torsion springs, which support the mirror plate and offer a restoring torque, and two pairs of electrodes attached to the mirror plate and glass substrate. The dimensions of mirror plate and torsion springs were determined so that a 5 V dc bias ±4.5 V ac drive voltage would provide the mirror with ±0.02° rotation to transmit laser beam spot on spinning disk. The MEMS-based milli-mirror was successfully fabricated using MEMS technology. Displacement–voltage linearization scheme was implemented by differential voltage driving. The static and dynamic performances of mirror prototype, such as capacitance versus driving voltage, rotation angle versus driving voltage, and resonant frequency were characterized and compared well with the simulation solutions. The mechanical resonant frequency of the mirror is expected to be high enough to satisfy the requirement of the servo bandwidth of precise tracking-control in high-density blue-laser optical disk drive.     

A novel hybrid 3D video service algorithm based on scalable video coding (SVC) technology

A scalable video coding (SVC) server can simultaneously provide a single bitstream with a fixed maximum service layer for different kinds of devices having different memory capacity, network bandwidth, and CPU performance requirements. An efficient hybrid 3D video service scheme is proposed without violation of the SVC standard technology for multiple transmission paths. A dynamic local disparity vector estimation algorithm is used to reflect the motion shift component between stereo views in the inter-layer prediction stage of the SVC encoder. To improve the coding efficiency, an adaptive search scheme based on distortion rates (DRs) between corresponding and reference macroblocks is used. Based on experimental results, up to 1.41 dB of quality improvement using JSVM 9.19 reference software is verified.     

A finite element method with discontinuous rotations for the Mindlin–Reissner plate model

We present a continuous-discontinuous finite element method for the Mindlin–Reissner plate model based on continuous polynomials of degree k ? 2 for the transverse displacements and discontinuous polynomials of degree k ? 1 for the rotations. We prove a priori convergence estimates, uniformly in the thickness of the plate, and thus show that locking is avoided. We also derive a posteriori error estimates based on duality, together with corresponding adaptive procedures for controlling linear functionals of the error. Finally, we present some numerical results.     

Solving online dynamic time-linkage problems under unreliable prediction

Dynamic time-linkage optimization problems (DTPs) are a special class of dynamic optimization problems (DOPs) with the feature of time-linkage. Time-linkage means that the decisions taken now could influence the problem states in future. Although DTPs are common in practice, attention from the field of evolutionary optimization is little. To date, the prediction method is the major approach to solve DTPs in the field of evolutionary optimization. However, in existing studies, the method of how to deal with the situation where the prediction is unreliable has not been studied yet for the complete Black-Box Optimization (BBO) case. In this paper, the prediction approach EA + predictor, proposed by Bosman, is improved to handle such situation. A stochastic-ranking selection scheme based on the prediction accuracy is designed to improve EA + predictor under unreliable prediction, where the prediction accuracy is based on the rank of the individuals but not the fitness. Experimental results show that, compared with the original prediction approach, the performance of the improved algorithm is competitive.     

A finite element creep crack growth model for Waspaloy

Plastic and creep deformations lead to reduced stress levels ahead of the crack tip in a creep crack growth test. However, they can also cause microcracks, cavities and other defects forcing fracture. Numerous damage models are reported in the literature to describe the behavior. In this article, a damage model will be developed from different theories and will be used to describe the creep crack growth behavior of Waspaloy at 973 K. Material parameters for this model are adjusted to uniaxial creep and tensile tests. The calculated creep crack growth curves match very well with the experimental ones supporting the model.     

Do badges increase user activity? A field experiment on the effects of gamification

During recent years, the practice of adding game design to non-game services has gained a relatively large amount of attention. Popular discussion connects gamification to increased user engagement, service profitability, goal commitment and the overall betterment of various behavioral outcomes. However, there is still an absence of a coherent and ample body of empirical evidence that would confirm such expectations. To this end, this paper reports the results of a 2 year (1 + 1 year – between-group) field experiment in gamifying a service by implementing a game mechanic called ‘badges’. During the experiment a pre-implementation group (N = 1410) was monitored for 1 year. After the implementation, the post-implementation (the gamified condition) group (N = 1579) was monitored for another full year. Results show that users in the gamified condition were significantly more likely to post trade proposals, carry out transactions, comment on proposals and generally use the service in a more active way.     

Shape optimization for 2-D mixed-mode fracture using Extended FEM (XFEM) and Level Set Method (LSM)

Weight and service life are often the two most important considerations in design of structural components. This research incorporates a novel crack propagation analysis technique into shape optimization framework to support design of 2-D structural components under mixed-mode fracture for: (1) maximum service life, subject to an upper limit on volume, and (2) minimum weight subject to specified minimum service life. In both cases, structural performance measures are selected as constraints and CAD dimensions are employed as shape design variables. Fracture parameters, such as crack growth rate and crack growth direction are computed using extended finite element method (XFEM) and level set method (LSM). XFEM employs special enrichment functions to incorporate the discontinuity of structural responses caused by the crack surfaces and crack tip fields into finite element approximation. The LSM utilizes level set functions to track the crack during the crack propagation analysis. As a result, this method does not require highly refined mesh around the crack tip nor re-mesh to conform to the geometric shape of the crack when it propagates, which makes the method extremely attractive for crack propagation analysis. An accurate and efficient semi-analytical design sensitivity analysis (DSA) method is developed for calculating gradients of fracture parameters. Two different approaches—a batch-mode, gradient-based, nonlinear algorithm and an interactive what-if analysis—are used for optimization. An engine connecting rod example is used to demonstrate the feasibility of the proposed method.     

Computational service life estimation of contacting mechanical elements in regard to pitting

A computational model for determining the service life of contacting surfaces in regard to surface pitting is presented. The model considers the material fatigue process leading to pitting, i.e. the conditions required for the short fatigue crack propagation originating from the initial crack in a single material grain. In view of small crack lengths observed in surface pitting, the simulation takes into account the short crack growth theory. The stress field in the contact area and the required functional relationship between the stress intensity factor and the crack length are determined by the finite element method. An equivalent model of two contacting cylinders is used for numerical simulations of crack propagation in the contact area. On the basis of numerical results, and with consideration of some particular material parameters, the probable service life period of contacting surfaces is estimated for surface curvatures and loadings that are most commonly encountered in engineering practice.     

Using electromyography responses to investigate the effects of the display type,viewing distance,and viewing time on visual fatigue

The rapid success of 3D display technology and daily accessibility to 3D images has greatly increased the interest in such applications for a wide range of fields. This paper compares the effects of watching movies with 2D and 3D displays depending on the viewing distance (3H vs. 6H, where H is the height of the screen) and viewing time to determine the visual fatigue using electromyography (EMG) in terms of the percentage of maximum voluntary contraction (%MVC) of the orbicularis oculi (OO) muscle activity and a subjective visual discomfort score. Twenty healthy male university students with a mean age of 27.7 ± 2.53 years participated in this study as volunteers. None had color blindness, and all had normal vision acuity. A mixed-measures design was performed. The results showed that the viewing time and distance had significant effects on the %MVC and OO muscle activity depending on the display type. Watching the 3D display from a short viewing distance produced significantly high visual fatigue compared to watching the 2D display from a short viewing distance. However, the 3D display seemed to be less stressful than the 2D display at long viewing distances.     

Experimental blood glucose interval identification of patients with type 1 diabetes

Many problems are confronted when characterizing a type 1 diabetic patient such as model mismatches, noisy inputs, measurement errors and huge variability in the glucose profiles. In this work we introduce a new identification method based on interval analysis where variability and model imprecisions are represented by an interval model as parametric uncertainty.The minimization of a composite cost index comprising: (1) the glucose envelope width predicted by the interval model, and (2) a Hausdorff-distance-based prediction error with respect to the envelope, is proposed. The method is evaluated with clinical data consisting in insulin and blood glucose reference measurements from 12 patients for four different lunchtime postprandial periods each.Following a “leave-one-day-out” cross-validation study, model prediction capabilities for validation days were encouraging (medians of: relative error = 5.45%, samples predicted = 57%, prediction width = 79.1 mg/dL). The consideration of the days with maximum patient variability represented as identification days, resulted in improved prediction capabilities for the identified model (medians of: relative error = 0.03%, samples predicted = 96.8%, prediction width = 101.3 mg/dL). Feasibility of interval models identification in the context of type 1 diabetes was demonstrated.     

Performance analysis of networks of queues under active queue management scheme

Analysis of networks of queues under repetitive service blocking mechanism has been presented in this paper. Nodes are connected according to an arbitrary configuration and each node in the networks employs an active queue management (AQM) based queueing policy to guarantee certain quality of service for multiple class external traffic. This buffer management scheme has been implemented using queue thresholds. The use of queue thresholds is a well known technique for network traffic congestion control. The analysis is based on a queue-by-queue decomposition technique where each queue is modelled as a GE/GE/1/N queue with single server, R (R ⩾ 2) distinct traffic classes and {N = N₁, N₂, … , N_R} buffer threshold values per class under first-come-first-serve (FCFS) service rule. The external traffic is modelled using the generalised exponential (GE) distribution which can capture the bursty property of network traffic. The analytical solution is obtained using the maximum entropy (ME) principle. The forms of the state and blocking probabilities are analytically established at equilibrium via appropriate mean value constraints. The initial numerical results demonstrate the credibility of the proposed analytical solution.     

CAE在同步辐射装置挡光元件设计中的应用

针对第三代同步辐射装置挡光元件承受极高热负载、设计难度大的问题,综述CAE在其设计中的应用情况:借助有限元分析可以获得挡光元件关键部件吸收体的最高温度和最大应力这两个最主要设计参数;通过计算流体力学(Computational Fluid Dynamics,CFD)软件模拟可以获得吸收体中冷却管道的对流换热与流动阻力特性参数;采用热弹塑性有限元分析可以获得用于低周疲劳寿命预估的吸收体热应力应变迟滞循环.下一步工作将围绕当今研究的核心问题——基于低周疲劳的设计准则展开,包括同步辐射高热负载作用下低周疲劳裂纹的起裂寿命和扩展寿命预测,以及吸收体倾角、表面光滑度、冷却管道排布等对寿命的影响.这些研究均需要充分利用CAE的强大分析功能.     

Bivariate quality control using two-stage intelligent monitoring scheme

In manufacturing industries, it is well known that process variation is a major source of poor quality products. As such, monitoring and diagnosis of variation is essential towards continuous quality improvement. This becomes more challenging when involving two correlated variables (bivariate), whereby selection of statistical process control (SPC) scheme becomes more critical. Nevertheless, the existing traditional SPC schemes for bivariate quality control (BQC) were mainly designed for rapid detection of unnatural variation with limited capability in avoiding false alarm, that is, imbalanced monitoring performance. Another issue is the difficulty in identifying the source of unnatural variation, that is, lack of diagnosis, especially when dealing with small shifts. In this research, a scheme to address balanced monitoring and accurate diagnosis was investigated. Design consideration involved extensive simulation experiments to select input representation based on raw data and statistical features, artificial neural network recognizer design based on synergistic model, and monitoring–diagnosis approach based on two-stage technique. The study focused on bivariate process for cross correlation function, ρ = 0.1–0.9 and mean shifts, μ = ±0.75–3.00 standard deviations. The proposed two-stage intelligent monitoring scheme (2S-IMS) gave superior performance, namely, average run length, ARL₁ = 3.18–16.75 (for out-of-control process), ARL₀ = 335.01–543.93 (for in-control process) and recognition accuracy, RA = 89.5–98.5%. This scheme was validated in manufacturing of audio video device component. This research has provided a new perspective in realizing balanced monitoring and accurate diagnosis in BQC.     

Design,fabrication, and testing of MEMS solid propellant thruster array chip on glass wafer

This paper presents the internal ballistic design, fabrication procedure, and performance evaluation of a micro-electro mechanical systems (MEMS) solid propellant thruster array chip. The internal ballistic design was carried out to predict the performance of the thruster. Two different ignition models were used. The numerical results gave a maximum thrust of 3840 mN, and a total impulse of 0.42 mNs at the local ignition model. A photosensitive glass wafer only was used as the bare material for the thruster. The stability of the micro-igniter was improved by using a glass membrane with a thickness of tens of microns. The average thickness of the membrane was 35 μm. The proposed micro-igniter had a level of power consumption appropriate to ignite the solid propellant. The thermal, electrical, and mechanical characteristics of the fabricated micro-igniter were measured. The solid propellant was loaded into the propellant chamber without resort to a special technique due to the high structural stability of the glass membrane. An MEMS solid propellant thruster (MSPT) array was fabricated through anisotropic etching of photosensitive glass. An ignition control system was developed to control the ignition sequence. Ignition and combustion tests of the fully assembly MEMS thruster were performed successfully. The minimum ignition delay was 27.5 ms with an ignition energy of 19.3 mJ. The average of the measured maximum thrust and total impulse were 3619 mN and 0.381 mNs, respectively.