Abstract: Based on the sidewall wrinkling phenomena in hydroforming of thin-walled Tee-joint, an analytical model for tube wrinkling under double side constraints was proposed to calculate the critical wrinkling stress. The effects of stress ratio, diameter-to-thickness ratio and tube material properties on critical condition of sidewall wrinkling were investigated. It is found that the middle of the main tube side wall is the most dangerous position for wrinkling within hydroforming of thin-walled Tee-joint. At a certain internal pressure, the critical wrinkling stress increases with increasing of ratio of hoop stress to axial stress and material strength coefficients, but decreases with increasing of work-hardening exponent and ratio of diameter to thickness. Through the analytical model combining FEM simulation, the critical wrinkling loading path according to the relation between axial feeding and internal pressure was obtained. Experimental results validates that wrinkle can be avoided if the pressure is above the critical wrinkling loading path, otherwise, wrinkle occurs. It is also verified that the analytical model of critical wrinkling stress is reasonable for the thin-walled Tee-joint hydroforming process.

Abstract: Objectives This study determines the following for a hypertensive patient population: 1) the prevalence of patient worldview clusters; 2) differences in medication adherence across these clusters; and 3) the adherence predictive power of the clusters relative to measures of patients' concerns over their medication's cost, side effects, and efficacy. Methods Members from patient panels in the UK, Germany, Italy, and Spain were invited to participate in an online survey that included the Medication Adherence Report Scale-5 (MARS-5) adherence instrument and a patient segmentation instrument developed by CoMac Analytics, Inc, based on a linguistic analysis of patient talk. Subjects were screened to have a diagnosis of hypertension and treatment with at least one antihypertensive agent. Results A total of 353 patients completed the online survey in August/September 2011 and were categorized against three different behavioral domains: 1) control orientation (n=176 respondents [50%] for I, internal; n=177 respondents [50%] for E, external); 2) emotion (n=100 respondents [28%] for P, positive; n=253 respondents [72%] for N, negative); and 3) agency or ability to act on choices (n=227 respondents [64%] for H, high agency; n=126 [36%] for L, low agency). Domains were grouped into eight different clusters with EPH and IPH being the most prevalent (88 respondents [25%] in each cluster). The prevalence of other behavior clusters ranged from 6% (22 respondents, INH) to 12% (41 respondents, IPL). The proportion of patients defined as perfectly adherent (scored 25 on MARS-5) varied sharply across the segments: 51% adherent (45 of 88 respondents) for the IPH vs 8% adherent (2 of 25 respondents) classified as INL. Side effects, being employed, and stopping medicine because the patient got better were all significant determinants of adherence in a probit regression model. Conclusion By categorizing patients into worldview clusters, we identified wide differences in adherence that can be used to prioritize interventions and to customize adherence messages. Also, the predictive power of segments was greater than that for variables measuring concerns over cost, side effects, and efficacy.

Abstract: Dispersion compensation is a vital issue in Lamb wave identification. Except for time reversal process (TRP), the commonly used compensation methods require the priori-knowledge of Lamb wave dispersion characteristics, which is usually derived in theory using the structure material parameters. However, the parameters could be probably unavailable, making the theoretical wavenumber relations hard to be attained. For the practical situation and considering the complexity of absolute wavenumber determination, linearly dispersive signal construction (LDSC) is presented for dispersion compensation of Lamb waves in this paper. LDSC can be performed not only with theoretical wavenumber curves but also with relative wavenumber curves, which can be easily measured without any structure material parameters. Thus, LDSC has high potential in Lamb wave detection for unknown structures. After the basic LDSC principle is fully explored based on the sensing model simplified in frequency domain, the numerical realization for LDSC is discussed. Then, a narrowband spectroscopy method is introduced for relative wavenumber curve measurement, and the applicability of LDSC with the measured relative wavenumber curves is theoretically investigated, which is subsequently validated with an aluminum plate experiment. Finally, associated with the traditional delay-and-sum algorithm, LDSC is used, as a typical application instance, for high spatial resolution Lamb wave imaging. The efficiency of the proposed LDSC and LDSC-based imaging is demonstrated by the experimental study on a glass fiber reinforced composite plate with unknown material parameters.

Abstract: A new fibre metal laminate fabricated with aluminium sheets and unidirectionally arrayed chopped strand (UACS) plies is proposed. The UACS ply is made by cutting parallel slits into a unidirectional carbon fibre prepreg. The UACS/Al laminate may be viewed as aluminium laminate reinforced by highly aligned, discontinuous carbon fibres. The tensile behaviour of UACS/Al laminate, including thermal residual stress and failure progression, is investigated through experiments and numerical simulation. Finite element analysis was used to simulate the onset and propagation of intra-laminar fractures occurring within slits of the UACS plies and delamination along the interfaces. The finite element models feature intra-laminar cohesive elements inserted into the slits and inter-laminar cohesive elements inserted at the interfaces. Good agreement are obtained between experimental results and finite element analysis, and certain limitations of the finite element models are observed and discussed. The combined experimental and numerical studies provide a detailed understanding of the tensile behaviour of UACS/Al laminates.

Abstract: This paper reports the low-cyclic tensile responses of three-dimensional orthogonal woven composites based on the micro/meso-scale repetitive unit cells with elastic/viscoelastic models. The repetitive unit cell models for the resin impregnated fiber tows and the three-dimensional orthogonal woven composites at the fabric microstructure level were established. In the micro/meso-repetitive unit cells model, a nonlinear viscoelastic relationship with switch rule is introduced to characterize the mechanical behavior of the resin for the loading/unloading conditions. The fiber/fiber tows are characterized with linear elastic models. And damage initiation and postdamage constitutive models are also included for matrix/fiber and matrix impregnated fiber tows in the finite element analysis. The fatigue model with the mechanical parameters transferred from micro-scale to meso-scale model is numerically simulated with user-defined material subroutine and incorporated into commercial finite element software ABAQUS/...

Abstract: In this paper, the influence of fiber length on the tensile behavior of fiber metal laminate, which is fabricated with unidirectionally arrayed chopped strand plies and aluminum sheets and named as...

Abstract: Scanning path for wing skin was planned automatically in advance in order to complete the scanning of wing skin quickly in the process of wing panel digital assembly.Wing skin was represented by a series of sampled points.These sampled points were divided into groups automatically based on least square method after explaining the theory of laser scanner and analyzing the scanning constraints such as scanning angle,depth and width.The scanning process was divided into two actions of alternating motion combination for scanning measurement and attitude adjustment.The objective function about how to make the scanning process as short as possible was created.Genetic algorithm was used to solve the problem so that the scanning path could be optimized in three dimensions.The new method was compared with the traditional methods such as trapezoidal scanning and line scanning method.Results show that the general scanning path of this method is shorter and use fewer attitudes.The average scanning efficiency was increased by 14.4%.The scanning simulation of robot with a scanner along the optimized path was completed,meeting all constraints requirements using DELMIA software platform,and the time of simulation was the same to the calculated value.

Abstract: The current aircraft maintenance philosophy, referred to as scheduled maintenance, follows a preventative strategy in which maintenance tasks are carried out at predetermined intervals or according to prescribed criteria related to safety, operational and economic aspects. Emerging technologies, such as structural health monitoring (SHM), are proposed to reduce long-term maintenance cost and increase aircraft availability. It introduces a timely and automatic diagnostic and prognostic capability which brings substantial changes to the current maintenance philosophy. This study investigates an integrated approach of scheduled maintenance and structural health monitoring by suggesting various logical maintenance procedures. A probabilistic model was established to examine the effects of the structural health monitoring synchronisation with scheduled maintenance and the impact on both safety and economy.

Abstract: Composites are getting more and more attention in the usage of major structures on ships owing to many advantages such as high specific strength and rigidity. However, composites are sensitive to impact, which indicates that the load-carrying capacity and stability of composite structures will decrease dramatically even for an invisible impact damage. Hence, a real-time impact monitoring system which has already been applied in aviation industry is important for reliability of ships, which inevitably encounter impacts during their lifetime due to different sources. This paper deals with the realization of an operational processing scheme to monitor the impact on composite structures, and estimate the impact location and load history by power distribution approach and system identification method. A PZT (piezoelectric lead zirconate titanate) sensor network was designed and employed to collect sensing signals for monitoring the impact. In the monitoring process, stress wave signals caused by impact were captured, and used to determine the impacted location and load history. Results demonstrate that the proposed method can be successfully applied in identifying the location and load history of impact on composite structures. The impact identification approach is of great significance for marine applications.

Abstract: Y2O3 crucibles have been prepared for as-cast Nb-22Ti-16Si-2Al-2Cr-2Hf and Nb-22Ti-16Si-2Al-2Cr alloys at 1950 °C. The microstructures, metal-crucible interfaces and contaminations were evaluated. Experimental results demonstrated that a mild interface reaction occurred between the Y2O3 crucibles and Hf, resulting in some inclusions dispersed in the metallic matrix. However, without Hf addition, no apparent reaction layers or inclusions were found. Both alloys were slightly contaminated with oxygen as the result of slow thermal dissociation of Y2O3, and its extent depended on Hf contents and holding times.

Abstract: This paper proposes a big-span position tracking algorithm based on pre-position time series to determine the user operation intention in virtual environment. Some problems, such as lost subject and inconvenient operation, when a tracker is working on big-scale models, like an airplane or a ship, can't be solved well in an immersive virtual reality system. Based on the moving trajectory and speed of a tracker in a unit of time span, the tracking algorithm is a plus to the mainstream relative position algorithm. The algorithm can tell the magnitude and intensity of a user's operation. It makes it especially convenient to display large-scale models in the CAVE system. Cases are used in this thesis to prove the effectiveness and convenience of this algorithm.

Abstract: In this study, we propose a new fiber metal laminate based on unidirectionally arrayed chopped strand (UACS) reinforced aluminum sheets, referred to as UACS/Al laminate. UACS is made by introducing slits into unidirectional carbon fiber-reinforced plastic (CFRP) prepreg. Due to the presence of discontinuous fibers, the microstructure of the UACS/Al laminate is much more complicated than the conventional fiber metal laminate, which also results in a failure progression that is more complicated. Tensile failure of the UACS/Al laminate might occur as combination of intra-laminar damage at the slits, inter-laminar damage at the interfaces, in-ply damage of the CFRP, and plastic deformation of the aluminum plies. Fabrication and tensile tests of UACS/Al laminate specimens were performed. A two-dimensional finite element model was developed with intra-laminar cohesive elements inserted into the slits of the UACS plies and with inter-laminar cohesive elements inserted into the interfaces between all laminas in t...

Abstract: The drive towards greater use of fiber-reinforced composites in primary structures, such as aircraft structures and wind turbines that are increasingly unitized, calls for advanced repair techniques that can restore the structural integrity and geometry. Two such repair techniques are stepped repairs and scarf repairs. Under certain conditions, stepped repairs are easier to perform than scarf repairs, but the step corners may cause high level of stress concentrations negatively affecting the strength of the repair. This paper presents an investigation of the effect of step corners on the fracture behavior of stepped joints under compressive loading, particularly after subjecting it impact damage. Joints featuring different corner radii were tested under compressive loading, and results showed that the impact damage reduced the compressive strength, to marginally below the compression-after-impact strength of composite laminates. The findings reveal that stepped repairs can be designed to rival the performance of scarf repairs, due to the similarity in the inherent stress concentrations at ply terminations in both repair configurations.