Heating at a propagating crack tip in a viscoplastic material

The crack tip temperature due to near-tip dissipation of mechanical energy has been calculated for a crack propagating in a viscoplastic material. The mechanical behavior of the material was represented by a model proposed by Bodner and Partom. On the basis of the adiabatic approximation the maximum temperature has been investigated as a function of the crack-tip speed and the material parameters. For a specific crack-tip speed, T _max is displayed as a function of the material constant, D ₀, which defines the asymptotic limit of the inelastic strain rate as the stress level increases. The maximum temperature increases with increasing values of D ₀.

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Résumé On calcule la température à l'extrémité d'une fissure occasionnée par la dissipation d'énergie mécanique d'une fissure en propagation dans un matériau viscoplastique. Le comportement mécanique du matériau est représenté par un modèle proposé par Bodner et Partom. Avec une approximation adiabatique, on étudie l'évolution de la température maximum en fonction de la vitesse de l'extrémité de la fissure et des paramètres du matériau. Pour une vitesse spécifique, on établit T _max en fonction d'une constante D ₀ qui définit la limite asymptotique de la vitesse de déformation lorsqu'augmente le niveau de contraintes. La température maximum augmente lorsque les valeurs de D ₀ s'accroissent.

     

Arrest of fast mode-i fracture in an elastic-viscoplastic transition zone

Arrest of a rapidly propagating Mode-I crack has been investigated for a crack which initially propagates in an elastic solid, and then enters a region of viscoplastic material properties. The transition to the viscoplastic behavior has been modeled by a gradual process which starts at a certain time at which the constitutive relations change in a time-wise manner from elastic to elastic-viscoplastic. The solution to the transient problem has been obtained numerically by a finite-difference procedure. Arrest of a crack in a perfectly elastic material has been treated as a special case. Field quantities such as the effective plastic strain, and the plastic work, have been computed, and their relation to arrest criteria have been explored. Both deformations in plane stress and plane strain have been considered.     

Calculation and Measurement of Scattering Coefficients for Surface-Breaking Cracks Sonified by a Focused Array

Abstract

A simulation of a focused beam of surface wave motion generated by a line array of surface wave transducers is used to calculate the field scattered back from a surface-breaking crack. The backscattered field is expressed in terms of a scattering coefficient, which is derived from the reciprocal identity for elastodynamic states, and which is calculated numerically by using the Kirchhoff approximation. In an earlier work the validity of the focused beam simulation has been verified. In this paper, the theoretical results for the backscattered field are compared with measurements for two crack sizes, one of which is used for calibration.     

Vereinfachte Bemessung brandbeanspruchter Stahlbetonkragstützen in Anlehnung an EC 2

Simplified Analysis for Cantilever Columns Exposed to Fire According to EC 2 This paper deals with the load bearing behavior of reinforced concrete cross‐sections exposed to fire. Examples show the governing influences. Hence, a simplified method for the structural fire design of reinforced concrete columns is realized. The use of this method is demonstrated in a worked example.     

Differential symptom expression and somatization in Thai versus U.S. children.

Individuals react in a variety of ways when experiencing environmental challenges exceeding their capacity to cope adaptively. Some researchers have suggested that Asian populations tend to react to excessive stress with somatic symptoms, whereas Western populations tend to respond more with affective or depressive symptoms. Other researchers, however, have suggested that such differences may represent different approaches to help seeking rather than actual variations in prevalence. The present study compared somatic versus affective symptoms in U.S. and Thai children from community and mental health clinic samples. In the clinic-referred sample, Thai children were reported to have higher levels of somatic versus depressive symptoms relative to U.S. children, whereas in the community sample, both groups were reported to have slightly higher levels of depressive than somatic symptoms. Because a primary difference between clinic-referred and community samples is that the former have been through the clinical referral process (i.e., were seeking help), these results suggest that differences in somatic versus depressive symptom presentation may be related to help-seeking behavior, at least for the samples involved in this study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Combined linear and homomorphic deconvolutions for processingbandpass measurements [US flaw detection]

The deconvolution presented is a combination of available techniques. It is effective for extracting the impulse response of individual flaws from ultrasonic data generated by flaw clusters. The technique requires output signals from both the flawed and unflawed systems. By combining linear deconvolution and homomorphic deconvolution, using the complex cepstrum, the desired impulse response can be extracted in cases where the signals contain overlapping wavelets. For the important case of bandpass signals, for which the complex cepstrum does not exist, the technique can still be applied by including a bandpass mapping in conjunction with homomorphic processing. Application of this combined approach to ultrasonic signals reflected from epoxy specimens produced the impulse response of a single cavity from measurements which were bandpass and contained overlapping signals from adjacent cavities. The recovered response, which compared well with the theoretical response of a single cavity, was sufficiently resolved to yield the radius of the spherical cavity     

Computation of heat transfer through a horizontally arranged HTR-fiber insulation

The heat transfer through a horizontally arranged ceramic fiber insulation operating at high pressure and temperature is studied theoretically. The contributions of heat conduction, natural convection and thermal radiation are considered. With an increasing value of the product of the Rayleigh and Darcy numbers, (Ra, Da), the natural convection is amplified, thus diminishing the efficiency of the thermal insulation. For high temperatures the thermal radiation is no longer negligible. The results of the computer code agree well with experiments available up to a temperature of 670 K and up to a pressure of 40 bar in helium or air. Finally, the heat transfer of a fiber insulation operating under high temperature reactor conditions is predicted, demonstrating that natural convection is nearly suppressed when an insulant bulk density of _b = 165 kg/m³ is provided.     

Sizing of disbonds at a thin-layer substrate interface from spectral peaks

An ultrasonic through transmission technique is used to inspect the interface of a thin layer and a substrate. An experiment is performed using a specimen constructed of a 0.040 inch (1.02 mm) polycarbonate layer bonded by an adhesive film to an aluminum plate. Circular flaws are induced with paper placed between the adhesive film and the polycarbonate layer to create disbonds. The flaws range in size from 0.5 inches (12.7 mm) to 0.067 inches (1.70 mm) in diameter. A through transmission ultrasonic inspection technique, which uses a flat transducer as a transmitter and a focused transducer as a receiver, is employed. Time signals from the receiving transducer are recorded for each flaw, transformed to the frequency domain by use of a fast Fourier transform (FFT), and are linearly deconvolved with the FFT of the time signals of the aluminum plate alone. The peaks of the resulting frequency response functions for each flaw predict the resonant frequencies of the flaws. The area of the thin layer above a disbond is modeled as a thin plate which is excited by the incident ultrasonic wave motion at its edges. The resonance peaks at the center of the plate are related to the size of the flaw. The principal result of the paper is that, based on the theory presented here, the size of the disbond can be obtained from measurements of the resonance peaks.     

Boundary-integral equation method for elastodynamic scattering by a compact inhomogeneity

The set of singular integral equations which relates unknown fields on the surface of the scatterer to a time-harmonic incident wave is solved by the boundary element method. The general method of solution is discussed in some detail for scattering by an inclusion. Results are presented for a spherical cavity, and for a soft and a stiff spherical inclusion. Fields on the surface of the scatterer are compared with previous results obtained by different methods. Back-scattered and forward-scattered displacement fields are presented, both as a function of position at fixed frequency, and as a function of frequency at fixed position. The quasi-static approximation is briefly discussed.     

Accelerating longitudinal research on child psychopathology: A practical example.

Accelerated longitudinal analyses link longitudinal data obtained for multiple birth cohorts. These analyses were used to determine whether longitudinal data obtained on children in 1 cohort could predict outcomes of psychopathology in another cohort. Seven cohorts of Dutch children were assessed 5 times at 2-yr intervals. Individual Ss from different cohorts were matched on Child Behavior Checklist total problem scores at 2 ages. Over 2-, 4-, and 6-yr intervals, between cohort correlations were nearly as high as within-cohort correlations. However, between-cohort correlations were only similar to within-cohort correlations when they included at least 1 of the 2 ages at which Ss were matched. The results support accelerated longitudinal analysis as a method of combining short-term longitudinal studies of behavioral-emotional problems into a longer longitudinal study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)