Sensitivity analysis of simulations for magnetic particle inspection using the finite-element method

Magnetic particle inspection (MPI) is widely used for nondestructive evaluation in aerospace applications in which interpretation of inspection results is currently limited to empirical knowledge and experience-based approaches. Advances in computational magnetics, particularly the use of finite-element calculations, have enabled realistic numerical simulations of magnetic particle inspection to be undertaken with complicated geometries. In this paper, we report a sensitivity analysis using finite-element-method simulations of magnetic particle inspection for defects with various sizes and geometries. As a result, improved quantitative understanding of the MPI technique and factors that affects its sensitivity and reliability has been achieved. These results can be used to optimize conditions for conducting these inspections and should lead to improvement in analysis and interpretation of experimental results.     

Thermischer Komfort – die extraphysikalischen Aspekte

Extraphysical parameters of thermal comfort. Standards define thermal comfort as a function of physical and thermophysiological parameters. From investigations of building related symptoms it is well known that satisfaction with the indoor environment also interacts with extraphysical parameters. Thus, data of 1,497 office workers investigated in phase II of the ProKlimA study have been analysed by multiple logistic regression to find associations between thermal sensation or comfort and potential non‐environmental variables. The results show diverse effects: While thermal sensation seems almost independent from non‐environmental impacts, thermal comfort and satisfaction with the indoor temperature are significantly associated with building characteristics, demographic and job related variables. From these significant and partly strong interactions we conclude, in case of analyses and assessment of complaints about thermal discomfort relevant non environmental impact factors should be considered.     

Comparison of risk factor profiles concerning self-reported skin complaints and objectively determined skin symptoms in German office workers

The correspondence between impact factor profiles of self-reported skin sensation and of objectively determined skin symptoms was examined using data from the ProKlimA project (1994-1999). A sub-sample of 925 office workers participated in measurements of skin hydration and sebum content and responded to a questionnaire assessing sensory perception. The calculation of multiple logistic regression models revealed a significant increased risk for female sex [Odds ratio (OR): 2.3; confidence interval (CI): 1.4-3.6], poor software (OR: 2.2; CI: 1.3-4.0), unfavorable job characteristics (OR: 1.8; CI: 1.1-2.8), allergic illness (OR: 1.5; CI: 1.1-2.2) and the use of skin cream (OR:2.6; CI: 1.6-4.4) on the subjective perception of skin sensation. Regarding the objective medical examination of the skin humidity a significant increased risk was detected for a high concentration of Total Volatile Organic Compounds (OR: 2.5; CI: 1.3-4.8) and a low relative humidity (OR:1.9; CI: 1.1-3.4). The likewise objectively measured low sebum content is not associated with environmental variables. The impact profiles on subjective vs. objective outcome variables differ in a clear and typical way. Skin related sensory perception is mainly influenced by job-related and personal impacts. Indoor environmental characteristics affect skin hydration. We conclude the need to develop, to adapt and to use objective clinical methods applicable for field monitoring parallel to questioning.     

Contacting surfaces: A problem in fatigue and diffusion bonding

Contact between surfaces usually occurs at asperities under compression or at connecting ligaments, depending on how the interface is formed. This paper deals with the nondestructive evaluation of the topology of contact and with the use of this information to predict the effects that loads borne by these contacts have on mechanical properties. Two specific examples are discussed: a fatigue crack and a diffusion bond. Asperity contact along the fracture surface of a fatigue crack partially shields the crack tip from the externally applied driving force. Using information from acoustic experiments, the geometry of the asperities, the contacting stress, and the shielding stress intensity factor have been estimated. Acoustically, a diffusion bonded interface looks very similar to that joining the two sides of a partially closed crack. In this particular case, the acoustically determined geometry of well-bonded ligaments can be verified by fractography of destructively tested samples whose bond strength has also been determined. Models to determine the bond strength from the ligament geometry are being suggested.     

Dietary intake of middle-aged men from an East and a West German city after the German reunification: do differences still exist?

The purpose of this study was to examine the effect of four conditions that might improve oxygen transport and/or utilization during maximal exercise performance in individuals with spinal cord injury (SCI). Five males with tetraplegia (TP) and four males with paraplegia (PR) performed maximal arm cranking exercise in the following positions: 1) sitting; 2) supine; and 3) sitting with the addition of a) anti-gravity suit (anit-G), b) elastic stockings and abdominal binder, and c) functional electrical stimulation (FES) of the paralysed leg muscles. Peak power output (PO peak), peak oxygen uptake (VO2peak), peak heart rate (HR peak) and maximal systolic blood pressure were significantly lower in TP compared to PR for all conditions. A significant decrease in HR peak for PR, and a significant increase in VO2peak/kg for TP was seen during the supine compared to sitting condition. Respiratory exchange ratio (R) decreased significantly during the FES compared to the sitting condition in TP. No other changes were observed for any of the other conditions in either group. Improvements in central circulation previously reported during submaximal exercise for these four conditions did not result in a concomitant rise in maximal exercise performance. The results of this study suggest that the limitation in VO2peak for individuals with SCI is located peripherally (small active muscle mass) rather than centrally (heart or lungs).     

Quantifying the vibrothermographic effect

Vibrothermography, also known as Sonic IR and thermosonics, is a method for finding cracks through thermal imaging of vibration-induced crack heating. Due to large experimental variability and equipment which has, up to now, yielded mostly qualitative results, little data has been available to help quantify the vibrothermographic effect. This paper quantitatively evaluates the relationship between vibrothermographic crack heating, crack size, and vibrational stress in a series of tests on 63 specimens each of Ti-6-4 titanium and Inconel 718 at three different sites with different equipments. Test specimens are excited in a resonant mode. Infrared cameras record the crack heating, and vibrational stress is evaluated from the known vibrational mode shape combined with vibrational velocities measured using a laser vibrometer. Crack heating increases both with crack length and dynamic vibrational stress level. Data from all three sites gives similar probability of detection (POD) curves. The relationship of crack heating to crack size and vibrational stress will provide a means in the future to predict crack detectability based on vibration measurements.     

Concepts, services, and protocols of the new GSM phase 2+ generalpacket radio service

For almost three years the European Telecommunications Standards Institute (ETSI) has been working on the specification of the general packet radio service (GPRS) for the Global System for Mobile Communications (GSM). In the course of 1997 standardization will come to an end, and a first introduction of GPRS by a service provider or network operator is likely to take place in 1999. The new service will accommodate data connections with variable bit rates and high bandwidth efficiency, and thus offers the possibility to attract a wide range of new applications to GSM networks. In this article possible applications and elementary concepts and service characteristics of GPRS are explained in detail. Furthermore, a medium access control protocol that conforms to the draft standard proposal for the GPRS air interface is introduced and analyzed. Thereafter, the simulation model is described and simulation results presented. The performance analysis carried out shows reasonable performance even under high load conditions