Search results

Eddy current testing is a frequently used NDT method at Saab/CSM but recently only single frequency testing has been used. The purpose of our work was to increase both testing speed and sensitivity by using multi‐frequency eddy current testing combined with a scanning system for corrosion detection in multi‐layered structures. The wing of the Saab 2000 aircraft was one specific example for which several samples were manufactured with both artificial (chemically etched) corrosion of various severity and cracks. Using previously determined optimal single frequency as a start, frequency combinations were determined to give increased detectability for the different structures and defects. The influence of different disturbing signals, e.g. signals from rivets, thickness variations, noise, and how to reduce them using the multi‐frequency technique was studied. Tests were also made in “field” conditions to evaluate the system.

Permittivity and dissipation factor (D_k and D_f) are effects of polarization of different components of the dielectric substrate material when subjected to an electrical field. A database of these important design parameters for PWBs has been developed for Thermount RT. Effects of variations in the level of moisture (bone‐dry to completely saturated at various relative humidity levels), testing temperature (room temperature to 120uC) and testing frequencies (1MHz to 1.5GHz) on D_k and D_f are reported. As the frequency of test is increased from 1MHz to 1.5GHz, the effect of moisture on the properties is reduced. Comparison with conventional glass/FR4 laminate properties shows the distinct advantage of Thermount. It is increasingly used in high frequency cellular telephone, satellite, and wireless applications which require HDI PWBs to achieve the highest packaging density at the lowest cost and weight.

Corrosion‐fatigue testing using precracked specimens has, in recent years, become an important means of evaluating structural alloys for service in corrosive environments. The recent emphasis towards the use of precracked specimens for corrosion‐fatigue testing is based upon several factors. First, there is the general recognition that metallic structures of all types are prone to contain cracks and that the growth of such cracks can play a crucial role in overall structural performance; and secondly, a fracture mechanics technology basis has been developed for quantitatively assessing crack growth phenomena. The coexistence of a visible problem area and a means of attacking the problem has stimulated considerable activity in this field of endeavour.

Fatigue crack growth (FCG) tests on lead‐containing solders and lead‐free solders have been carried out at frequencies ranging from 0.01 to 10 Hz and stress ratios in the range 0.1–0.7. The FCG resistance of lead‐free solders was found to be superior to that of lead‐containing solders. For both types of solder, cycle dependent behaviour is dominant for the tests at low stress ratios and high frequencies, while time‐dependent effects become important at high stress ratios and low frequencies. For cycle dependent testing conditions, cracks primarily propagated in a transgranular manner, while a mixed trans/intergranular mode of crack propagation was observed for testing conditions where time dependent effects were dominant. The propagation path of intergranular cracks depended on the test materials, and along interfaces. After the FCG tests, the formation of small grains was observed.

One concern that has slowed the progress of surface mounted technology, in particular leadless chip carriers, has been the question of the reliability of the surface mount attachment technology. This concern follows from the realisation that the functional reliability of surface mount technology is a very complex issue involving many not very well understood components. What is needed is a relatively simple, useful, predictive model. The model reported here sidesteps the numerous complex underlying issues, which, if considered separately, make a predictive reliability model all but impossible, by taking a purely phenomenological approach and relegating second‐order effects to a lumped empirical figure of merit.

This article concerns the experimental investigations of the effect of frequency of cyclic stressing on the reversed bend fatigue strength of the aluminium alloys 4·4 per cent Cu‐Mg‐Si‐Mn (L.70, L.71, L.72 and L.73) and the 5 per cent Zn‐Mg‐Cu type (D.T.D.687) over the frequency range 10 to 1,000 cycles per second. The central theme of the theoretical analysis of the experimental work has been based on the working hypothesis that the so‐called frequency effect on fatigue strength, as normally measured by fatigue tests in air, contains, in most cases, an appreciable corrosion fatigue factor together with the true frequency effect. The corrosion fatigue factor, being time and frequency dependent, becomes dominant after an appreciable time exposure whilst the true frequency effect recedes to insignificance. This state of affairs becomes reversed when considering fatigue strength on a much shorter time basis. A study of the kinetics of corrosion fatigue, and fatigue under normal ambient conditions where complete corrosion protection has been afforded, has led to a method whereby the true frequency effect can be separated from the net effect of corrosion and frequency as measured by ambient fatigue strength values. The extraction of the true frequency effect by this method has resulted in its formulation thus:

Surface insulation, electrochemical migration and various other insulation resistances are terms which are often glibly used, sometimes even incorrectly. This paper categorises different types of insulation resistance and catalogues about twenty practical applications of insulation resistance measurement, each with its ideal general conditions of measurement (test voltage, bias voltage, bias polarity, test voltage period, test frequency, test duration, temperature, humidity, test pattern type, test pattern dimensions, voltage gradients, tolerances, etc.) This description is independent of any of the nearly forty known, often contradictory, standards, most of which no longer correspond to the practical printed circuit or assembly of today. Also discussed are the different technologies of insulation resistance measurement, starting with the original non‐electronic ‘Megger®’ types through to modern laboratory electrometers and, finally, instrumentation specific to the practical measurement of printed circuit insulation resistances, including static and dynamic types. The importance of automatic statistical analyses is emphasised, especially with production testing as well as qualification procedures. This paper is aimed not only at those wishing to learn what modern insulation resistance testing is all about, but also at experienced persons wanting to marshall their thoughts about the fundamental meanings of insulation testing for different applications and specifications.

The purpose of this study is to attempt to analyze Granger causality in the frequency domain framework between producers' prices measured by wholesale price index (WPI) and consumers' prices measured by consumer price index (CPI) in the context of India.

Analysis was carried out in the framework of time series and for analysis Johansen and Juselius's maximum likelihood approach for cointegration was applied after confirming that variables are integrated of order one, i.e. I(1) through the Lee and Strazicich unit root test. Finally, Granger causality was tested in the frequency domain by utilizing a recently developed approach of Lemmens et al. over the period January 1957‐February 2009.

The paper finds that CPI Granger cause WPI at a lower, intermediate as well as higher levels of frequency, reflecting very long‐run, intermediate as well as short‐run cycles. By contrast WPI Granger cause CPI at 5 percent level of significance was found at intermediate frequencies, reflecting significant intermediate cycles.

The study reveals that CPI is a leading indicator of producers' prices and inflation (i.e. WPI). This gives an indication that Indian policy analysts ought to control for factors affecting CPI in order to have control on WPI since WPI is used for making various macroeconomic indicators in real terms.

The main contribution of the paper is to show the evidence of bidirectional causality between WPI and CPI. Furthermore, use of a recent approach developed by Lemmens et al. for Granger causality in the frequency domain in this study is also relatively new. To the best of the author's knowledge there is no such study in this area either for developed or developing economy to date.

The purpose of this paper is to experimentally investigate the capability of four non-destructive testing (NDT) techniques to detect the layer orientation in textile composite laminates. The aerospace industry has been the primary driving force in the use of textile composites.

Woven glass fiber composite samples were inspected using C-scan ultrasonic, vibration analyzer, X-ray micro-tomography and ultraviolet technique. In a complementary study, mechanical testing was carried out to investigate the effect of mid-layer orientation on in-plane tensile strength and their failure modes using microscopic imagining.

During C-scan ultrasonic, the high attenuation and scattering of ultrasonic waves caused by the textile fabric layers limited its application to only detect the first layer of samples. Frequency response tests of composite samples were also conducted to investigate the effect of mid-layer orientation on dynamic responses. The same trend was observed in the finite element modeling results with a clear effect of the fiber orientation defect seen in frequency response function response and higher mode shapes. Moreover, the results of micro computed tomography demonstrate that this technique could definitely detect the orientation of each layer; however, X-ray imaging at small scales introduced some challenges. Images obtained from ultraviolet technique did not reveal mid-layer orientation.

In this paper, the application of different NDT techniques along with finite element modeling to inspect two-dimensional textile composites was presented. Hopefully, the research results presented here will lead to much published papers in inspection of textile composites.

The purpose of this paper is to explore the moderating effect of brand exposure time and exposure frequency in image transfer. In study 1, H1 and H2 assumed the bidirectional image transfer (i.e. from an event to a brand, from a brand to an event). H3 and H4 were set to examine the moderating effect of brand exposure time and exposure frequency in image transfer upon spreading activation theory, mere exposure effect and three-hit theory.

According to study 1, the result indicated that the amount of image transfer varied based on the exposure time. However, brand exposure frequency did not show statistically significant interactions. Study 2 was performed to complement the H4 of the study 1. In study 2, apart from the number of exposures on a screen (group 1=four times; group 2=eight times), the perceived number of exposures were separately measured (group 1=2.67; group 2=3.96) to see if the number of perceived exposures moderated the amount of image transfer.

The results indicated that there was no group difference in the amount of image transfer. Based on the result of the study, a sponsor brand must be exposed for enough time duration in order to maximize the return on investment regardless of how frequently it is exposed.

The current study examined the image transfer in sport sponsorship. Although previous studies empirically examined the image transfer phenomenon in sport sponsorship, they failed to establish theoretical ground. Thus, this study incorporated the three theories in advertising and examined how we can apply the theories to sport sponsorship. In addition, we examine the image transfer based on video clip which is mainly how people are exposed to sport sponsorship. Next, we examined the moderating effects of exposure duration and exposure frequency, which has never been studied in sport sponsorship context.