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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.

As more courses move to online testing, it is important to understand how it can be used to enhance student learning. Adopting online testing strategies which have been documented to be effective (including increasing the frequency of testing, allowing the students to take the test “open book” and allowing the students two opportunities to take each test) may enhance student learning. This study assesses whether adopting these strategies, facilitated by online testing, leads to greater student learning.

I gathered data from eight sections of an undergraduate auditing course in which students in four sections of the class were tested using six online tests taken by the students outside of class. These six online tests were “open book” and allowed the students two opportunities to take each test. Scores from a common final exam are then compared to those from four sections of the same course where three in-class, traditional paper tests were administered. I also surveyed the online test group to gather information regarding their perceptions of online testing.

Students in the online group scored significantly higher on the tests and the final exam. Additionally, the online group reported a positive perception about their experience with online testing.

Online testing did not impair students’ learning, and if the testing environment is designed correctly, online testing may increase student learning.

Instructors considering introducing online testing should consider introducing some of the specific strategies and practical implications described in the chapter to increase student learning.

This article proposes a new approach to detecting the presence of common cyclical features when several time series are sampled at different frequencies. We generalize the common-frequency approach introduced by Engle and Kozicki (1993) and Vahid and Engle (1993). We start with the mixed-frequency VAR representation investigated in Ghysels (2012) for stationary time series. For non-stationary time series in levels, we show that one has to account for the presence of two sets of long-run relationships. The first set is implied by identities stemming from the fact that the differences of the high-frequency I (1) regressors are stationary. The second set comes from possible additional long-run relationships between one of the high-frequency series and the low-frequency variables. Our transformed vector error-correction model (VECM) representations extend the results of Ghysels (2012) and are important for determining the correct set of variables to be used in a subsequent common cycle investigation. This fact has implications for the distribution of test statistics and for forecasting. Empirical analyses with quarterly real gross national product (GNP) and monthly industrial production indices for, respectively, the United States and Germany illustrate our new approach. We also conduct a Monte Carlo study which compares our proposed mixed-frequency models with models stemming from classical temporal aggregation methods.

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.