Material and finite element analysis of poly(tetrafluoroethylene) rotary seals

Abstract

The stress-strain characteristics of PTFE under uniaxial tension and compression have been measured at various temperatures. A new finite element analysis procedure using MARC is presented, which can simulate the different properties of PTFE from tension and compression data. This method is based on using the maximum principal stress value at the integration point of each element to define whether the element is under tension or compression at each increment, then using subroutines to specify the material properties. A positive value indicates a state of tension and a negative value indicates compression. It has been found that the finite element analysis results are in good agreement with those from experiment. Finally, a PTFE rotary seal was modelled using this new method, and results were obtained incorporating stress and lip loads of the rotary seal, with different temperature effects.     

Self-adaptive neuro-fuzzy systems for autonomous underwater vehicle control

This paper presents a systematic approach for developing a concise self-adaptive neurofuzzy inference system (SANFIS) with a fast hybrid parameter learning algorithm for on-line learning of the control knowledge for autonomous underwater vehicle (AUV) control. The multi-layered network structure of SANFIS incorporates fuzzy basis functions for better function approximations. We investigate three SANFIS structures with three different types of fuzzy IF-THEN rule-based models and cast the rule formation problem as a clustering problem. A recursive least-squares algorithm and a modified Levenberg-Marquardt algorithm with limited memory are exploited to accelerate the parameter learning process. This hybrid parameter learning algorithm together with an on-line clustering technique and rule examination provide SANFIS with the capability of selforganizing and self-adapting its internal structure (i.e. the fuzzy rules and term sets) for learning the required control knowledge for an AUV to follow desired trajectories. Computer simulations for modeling a control system for an AUV have been conducted to validate the effectiveness of the proposed SANFIS.     

Application of the dual-drop dual-crystal contact angle technique to characterize heavy oil reservoir wettability

Reservoir wettability characterization is often important for planning and predicting depletion strategies, including primary and enhanced recovery schemes. This paper compares wettability evaluations in terms of water-advancing contact angles measured using the recentlydeveloped 'dual-drop-dual-crystal (DDDC)' technique with the traditional 'modified sessile drop' procedure. The DDDC technique was found to be a more reliable method for the Elk Point crudeoil/brine/rock systems. The DDDC experimental procedure is less time consuming because this technique achieves rapid adsorption equilibrium between two crude oil drops and two crystal surfaces. Moreover, it is reproducible as it is designed to overcome the difficulties commonly associated with the traditional contact angle methods. On the basis of the DDDC contact angle experiments, it was concluded that both the Lindbergh and Frog Lake Cummings heavy oil reservoirs of the Elk Point field exhibited intermediate wettability near the native reservoir conditions (characteristic of primary depletion). The water-advancing contact angles for the crude-oil/brine/quartz systems (near the reservoir conditions of 4400 kPa and 28°C) were determined to be 92 and 90° for Lindbergh and Frog Lake systems, respectively. These angles were reproducible within 1°. This reproducibility is the result of meticulous application of wateradvancing contact angle definition by means of a procedure that recognizes the effects of adhesion and buoyancy and allows shifting of the lower crystal so that the brine advances over an area that was previously exposed to crude oil. In addition, a careful monitoring of three-phase (oil/water/solid) contact line movements ensures conformance to the definition of water-advancing contact angle as demonstrated in this paper.     

Quasi-static fracture toughness testing of a single CT specimen at two test conditions

Abstract

It is proposed that a single CT specimen can be used for determining J ₀.₂ at two testing conditions, provided it can be ensured that the crack tip plastic zones for the two tests do not interfere. This is achieved by extending the crack at the end of the first fracture test by fatigue cycling at ambient temperature to obtain the starting crack for the second test. This method has been validated by testing thermally aged CT specimens of modified 9Cr - 1Mo steel at 653 K and 803 K. The J-Δa values obtained by a multispecimen method at a specific temperature were on a single curve irrespective of whether the data were generated from the first test or second test on that sample. Also, the J-Δa curves obtained using a single specimen normalisation method from data on first and second tests were within the expected specimen to specimen variation.     

The vibration welding of poly(butylene terephthalate) and a polycarbonate/poly(butylene terephthalate) blend to each other and to other resins and blends

Vibration welding is used to assess the weldability of poly(butylene terephthalate) (PBT) and a polycarbonate/poly(butylene terephthalate) blend (PC/PBT) to each other and to other resins and blends: PBT to PC/PBT, PBT to modified poly(phenylene oxide) (M-PPO), PBT to polyetherimide (PEI) and PEI to a 65 wt% mineral-filled polyester blend (65-PF-PEB), PBT to a poly(phenylene oxide)/polyamide blend (PPO/PA), PC/PBT to M-PPO, and PC/PBT to PPO/PA. Based on the tensile strength of the weaker of the two materials in each pair, the following relative weld strengths have been demonstrated: PBT to PC/PBT,98%; PBT to PEI, 95%; 65-PF-PEB to PEI, 92%; and PC/PBT to M-PPO, 73%. PBT neither welds to M-PPO nor to PPO/PA, and PC/PBT does not weld to PPO/PA.     

Efficient recursive algorithm for the operational space inertia matrix of branching mechanisms

This article describes an efficient recursive algorithm for the computation of the operational space inertia matrix of an n-link branching robotic mechanism with multiple (m) operational points. The proposed algorithm achieves the complexity of O(nm + m ³). Since m can be considered as a small constant in practice, as the number of links increases, this algorithm performs significantly better than the existing O(n ³ + m ³) symbolic method. The experimental results of this algorithm are presented using real-time dynamic simulation.     

Investigation into use of side delaminations in interlaminar fracture mechanics

Abstract

Weft knitted glass fibre (GF) fabric reinforced poly(ethylene terephthalate) (PET) composite sheets were manufactured by hot pressing of stacked plain knitted fabric layers. The knits were produced from a commingled yarn containing 70 wt-% (≈50 vol.-%) GF. The reinforcing knits were stretched in the wale direction at various ratios prior to consolidation. The PET matrix of the composite was either amorphous or semicrystalline. The static mechanical performance of the knitted GF–PET composite sheets was studied in tension, compression, and flexure. Measurements were carried out on speci mens in both wale and course directions of the reinforcing knit in order to assess the structural anisotropy. The inherent anisotropy of the unstretched knit was well reflected in the strength data: the response in the wale direction was superior to that measured in the course direction. The mechanical anisotropy increased with increasing stretching of the knit. The dynamic perforation impact behaviour of the composites was determined by instrumented falling weight impact tests. The static and particularly the dynamic performance of the composites with amorphous PET was superior to that of the semicrystalline version.     

Measurement of Mode I and Mode II Fracture Properties of Wood-Bonded Joints

In this work, the fracture characterisation of wood-bonded joints under pure mode I and mode II loading was performed. The tested material was maritime pine (Pinus pinaster Ait.) bonded with an epoxy adhesive. Two fracture mechanical tests were chosen: the double cantilever beam (DCB) for opening mode I loading, and the end-notched flexure (ENF) for sliding mode II loading. The compliance-based beam method (CBBM) was used for both mode I and mode II fracture, since the Resistance-curves can be obtained directly from the global mechanical response of the specimens (load–displacement curve), without crack monitoring during propagation. This data reduction scheme was validated by direct comparison with the modified experimental compliance method (MECM).     

一种基于特征向量的超声图像配准方法

目前,超声图像的配准倍受关注。在MODIFIED HAMMER算法框架的基础上,针对其计算梯度幅值的求导运算在提取超声图像特征时易受斑点噪声影响的问题,基于斑点噪声的统计特性提出了一种新的参数特征用以取代梯度幅值,与LOG算子和灰度值组成特征向量,用于提取超声图像的重要特征点,并完成图像的配准。实验证明,该算法有效减少了重要特征点数目从而减少了配准时间,并且提高了配准精度。