Analysis of dynamic characteristics of structural joints using stiffness influence coefficients

This paper proposes a new modeling method for joints in mechanical structures in order to reduce the errors in eigenvalue analysis due to joint modeling. The new modeling method uses both a stiffness influence method and a condensation method to obtain the dynamic characteristic matrix of the joint region. It also employs the displacement and reaction of finely modeled finite element analysis in the calculation of stiffness influence coefficients. In order to check the validity of the proposed method, natural frequencies and mode shapes of a simple structure with a bolted joint are investigated by the proposed method and by experiments. The eigenvalue analysis using the proposed method shows more accurate results than that using rigid joints modeling, when the natural frequencies are compared with the experimental results. In addition, the differences between the natural frequencies obtained by the proposed method and those by the rigid joints modeling are notable in the modes where the joint has elastic deformation.     

Development of an automated progressive design system with multiple processes (piercing, bending, and deep drawing) for manufacturing products

This paper describes the research work involved in developing an automated progressive design system with multiple processes such as piercing, bending, and deep drawing for manufacturing products. This approach to make a progressive, flexible working system is based on knowledge-based rules. The knowledge required for this system is formulated from plasticity theories, experimental results, and the empirical knowledge of field experts. The system consists of three main modules: shape treatment, strip layout, and die layout modules. The system is founded on knowledge-based rules and is designed in consideration of several factors, such as the material and thickness of a product, the piercing, bending and deep drawing sequence, and the complexities of blank geometry and punch profiles. The system then generates the strip layout drawing for an automobile product. The die layout module carries out the die design for each process from the results of the strip layout module. The results obtained using the modules enable the designers of manufacturing products with multiple processes to be more efficient in this field.     

Dioxin emission factors for automobiles from tunnel air sampling in Northern Taiwan

This study measured PCDD/F concentrations in tunnel air and vehicle exhaust. The ambient air samples were collected with air samplers (Tisch PS-1) complying with USEPA TO-9A. The results indicate that the tunnel air had a PCDD/F TEQ concentration about two times as high as that of outside air (47.3 and 57.1 fg-I-TEQ/m3 for tunnel air vs. 37.1 fg-I-TEQ/m3 and 23.3 fg-I-TEQ/m3 for outside air, respectively). This provides the direct evidence that PCDD/F compounds are emitted from the combustion processes in gasoline- and diesel-fueled engines. According to the tunnel study, the emission factors ranged from 5.83 to 59.2 pg I-TEQ/km for gasoline vehicles and 23.32 to 236.65 pg I-TEQ/km of diesel vehicles. This indicates that the dioxin emission factor in Taiwan is lower than that measured in USA, Norway and Germany. When the speed of the diesel vehicle was set at 40 km/h, the dioxin concentration emitted from diesel vehicle was 278 pg/m3 (6.27 pg-I-TEQ/m3) from tailpipe testing. However, when the diesel vehicle was idled, the dioxin concentration increased greatly to 4078 pg/m3 (41.9 pg-I-TEQ/m3). From the results of tunnel air sampling, the PCDD/Fs emission from automobiles in Taiwan was estimated as 3.69 g I-TEQ per year.     

Toward Environmentally Robust Organic Electronics: Approaches and Applications

Recent interest in flexible electronics has led to a paradigm shift in consumer electronics, and the emergent development of stretchable and wearable electronics is opening a new spectrum of ubiquitous applications for electronics. Organic electronic materials, such as π‐conjugated small molecules and polymers, are highly suitable for use in low‐cost wearable electronic devices, and their charge‐carrier mobilities have now exceeded that of amorphous silicon. However, their commercialization is minimal, mainly because of weaknesses in terms of operational stability, long‐term stability under ambient conditions, and chemical stability related to fabrication processes. Recently, however, many attempts have been made to overcome such instabilities of organic electronic materials. Here, an overview is provided of the strategies developed for environmentally robust organic electronics to overcome the detrimental effects of various critical factors such as oxygen, water, chemicals, heat, and light. Additionally, molecular design approaches to π‐conjugated small molecules and polymers that are highly stable under ambient and harsh conditions are explored; such materials will circumvent the need for encapsulation and provide a greater degree of freedom using simple solution‐based device‐fabrication techniques. Applications that are made possible through these strategies are highlighted.     

Anisotropic threshold stress intensity factor, KIH and crack growth rate in delayed hydride cracking of Zr-2.5Nb pressure tubes

The objectives of this study are to systematically investigate the delayed hydride cracking (DHC) velocity and the threshold-stress intensity factor, K _IH , of a Zr-2.5Nb pressure tube as a function of orientation and elucidate the cause of this anistropic DHC behavior. The DHC velocity as a function of orientation was determined using flattened cantilever beam specimens with 60 ppm H while the threshold-stress intensity factor K _IH , was evaluated as a function of orientation on the curved compact-tension (CT) and cantilever-beam (CB) specimens charged with hydrogen to 200 ppm H. To infer a difference in a stress gradient ahead of the crack tip as a function of orientation, tensile tests were conducted at temperatures ranging from room temperature (RT) to 560 °C using small tensile specimens of 2-mm-gage length taken from three directions of the tube. A textural change was investigated by comparing the inverse pole figures before and after DHC while the {10 7} pole figures were constructed to find out the growth pattern of the DHC crack as a function of orientation. Faster DHC velocity and lower K _IH were obtained over temperatures of 170 °C to 270 °C, when the DHC crack grew in the longitudinal direction of the Zr-2.5Nb pressure tube. The strain hardening after yielding and the extent of the textural change accompanied by DHC were higher in the longitudinal direction of the tube, suggesting a higher stress gradient ahead of the crack tip. Thus, the anisotropic DHC behavior of a Zr-2.5Nb pressure tube is discussed based on the stress gradient ahead of the crack tip governed by strain-hardening rate after yielding and a change in texture accompanied by DHC, and the distribution of the {10 7} hydride habit planes. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Plasma-Assisted Process for Removing NO/NOx from Gas Streams with C2H4 as Additive

NOx removal from gas streams via dielectric barrier discharges (DBDs) has been experimentally evaluated. This paper investigates the effect of injecting C2H4 as an additive with respect to the De–NOx chemistry and the effect of gas composition on NO/NOx removal efficiencies. Experimental results indicate that both removal efficiencies of NO and NOx are enhanced with increasing applied voltage, gas temperature, and water vapor. Water vapor in gas streams has a distinct influence on NOx removal by generating OH radicals to convert NO2 to form HNO3. NOx removal decreases with increasing oxygen content although NO removal increases with increasing oxygen content. As high as 100% of NO and 57% of NOx are removed at 140°C for the gas stream containing [NO]:[C2H4]:[H2O(g)]:[O2]:[N2] = 0.05:0.2:3.0:5.0:91.75. Major mechanisms for NO and NOx removals in DBD processing with C2H4 as an additive are described in the text.     

A very low operation current InGaAsP/InP total internal reflectionoptical switch using p/n/p/n current blocking layers

A very low operation current (20 mA) has been achieved for the first time with an InGaAsP/InP total-internal-reflection optical switch. The optical switch is fabricated on an n⁺-InP substrate using p/n/p/n current blocking layers. This switch has a large effective contact area and is a self-aligned structure. This is a promising result for making optical integrated circuits     

Effect of an interfacial shear stress on steam condensation in the presence of a noncondensable gas in a vertical tube

Experimental and analytical studies were performed to examine local condensation heat transfer coefficients in the presence of a noncondensable gas inside a vertical tube. The experimental data for pure steam and steam/nitrogen mixture bypass modes were compared to study the effects of noncondensable nitrogen gas on annular film condensation phenomena. The condenser tube had a relatively small inner diameter of 13 mm. The experimental results demonstrated that the local heat transfer coefficients increased as the inlet steam flow rate increased and the inlet nitrogen mass fraction decreased. The results obtained using steam/nitrogen mixtures with a low inlet nitrogen mass fraction were similar to those obtained using pure steam. Therefore, the effects of noncondensable gas on steam condensation were weak in the small-diameter condenser tube because of interfacial shear stress. A new correlation based on dimensionless shear stress and noncondensable gas mass fraction variables was developed to evaluate the condensation heat transfer coefficient inside a vertical tube with noncondensable gas, irrespective of the condenser tube diameter. A theoretical model using a heat and mass transfer analogy and simple models using four empirical correlations were developed and compared with the experimental data obtained under various experimental conditions. The predictions of the theoretical model and the simple model based on a new correlation were in good agreement with the experimental results.