A micromechanical model for cleavage-crack reinitiation

A crack-tip screening analysis of cleavage fracture of steel is developed. The analysis incorporates evidence that reinitiation of an arrested cleavage crack requires less stress intensity than cleavage initiation from a fatigue precrack. Fractographic evidence as well as metallographic sectioning of arrested cracks have previously shown that the mechanism of rapid crack propagation by cleavage is affected strongly by partial crack-plane deflection which leaves unbroken ligaments in its wake. The tearing of these ligaments by dimple rupture is the dominant energy-absorbing mechanism. Earlier etch-pit experiments using an Fe-Si alloy showed that the crack-tip stress intensity based on plastic zone size is extremely low. These observations are incorporated into a model in which cleavage crack reinitiation is analyzed using a sharp crack that is shielded by a distribution of pinching forces along its faces. During reloading of the arrested crack, the ligaments restrict crack-tip blunting, leading to higher local stresses. As a result, lower stress intensities are needed for reinitiation than for initiation from a fatigue precrack.     

Connections to cerebellar cortex (Larsell's HVI) in the rabbit: A WGA-HRP study with implications for classical eyeblink conditioning.

Conditioned eyeblink responses are presumably learned in the cerebellum and relayed to motoneurons by way of the red nucleus. Projections from the red nucleus to cerebellar cortex (Larsell's lobule HVI) could be important for shaping temporally adaptive features of the conditioned response. Rabbits that had pipettes containing wheat germ agglutinated horseradish peroxidase (WGA-HRP) implanted unilaterally into HVI showed retrograde labeling of neurons within subregions of the contralateral red nucleus implicated in eyeblink conditioning by lesioning and recording studies. Retrogradely labeled neurons were also observed in the pontine nuclei, inferior olive, and spinal trigeminal nucleus pars oralis. Projections to HVI provide a possible neural substrate for implementing time-derivative computational models of learning in the cerebellum. Time-derivative models are capable of describing the timing and topography of conditioned responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Combined mode I-mode III fracture of a high strength low-alloy steel

Special formulations of theJ integral were used to quantify the combined mode I-mode III fracture behavior of ASTM A710 Grade A steel, a tough material which displays elastic-plastic behavior at room temperature. Experimental fracture initiation loci for two heat-treated conditions were linear inJ _i-J_iii space, agreeing with analytical predictions based on linear elasticity. As commonly observed in mode I fracture behavior, large tearing modulus values accompanied largeJ values for mode I and mode III components, individually as well as for totalJ values. There was a pronounced tendency toward antiplane shear flow in the modified compact tension specimens tested. This may result from the concentration of mode III shear strains in the plane of the propagating crack as predicted by slip line theory. Shear fractures with the crack propagating at inclined angles to both load line and plate free surfaces are favored energetically over pure mode I cracks even though the total surface area formed by the latter is much smaller.     

Analysis of Indentation Crack as a Wedge-Loaded Half-Penny Crack

Surface cracks produced by indentation with a Vickers indenter were modeled as half-penny cracks extended by symmetric disk-shaped wedges. The wedge diameter was assumed to be equal to the hemispherical plastic zone size, and the wedge thickness was calculated by equating the wedge volume to the hardness-impression volume. The resulting equilibrium relation between the indentation load and the radius of the half-penny crack is in good quantitative agreement with similar relations obtained from fracture toughness calibration.     

Optical rotation of petroleums

Although oils and oil distillates are usually dextrorotatory, some levorotations can be measured in lower boiling distillates. Fractional distillation of a Colombia crude oil of Eocene age showed that optical rotation is maximal at an average molecular weight of 464. The rotatory power of petroleum reflects the extent to which its composition has been transformed during geochemical maturation. Optical rotations thus can be correlated with the degree of maturity in much the same way as can such other compositional features as aromatic character or content of steroid-like substances, which are demonstrable in petroleums. The optical activity of petroleum is gradually degraded by maturational influences, and a decreasing trend in rotatory power is recognized in a comparison of oils produced from rocks of progressively greater geologic age. The optical rotation of dark crude oils can be measured in a polarimeter of suitable photometric sensitivity. The measurements extend geochemical application of oil polarimetry, which was restricted formerly to oil distillates and decolorized oils.     

Improving the effectiveness of computer-delivered personalized drinking feedback interventions for college students.

This study evaluated methods of enhancing college students' retention of information provided to them in a computer-delivered personalized drinking feedback intervention and whether enhanced retention reduced alcohol consumption during the two-week period following the intervention. Participants were 98 college students who reported at least one heavy drinking episode in the past two weeks. After participating in an online, personalized drinking feedback intervention, students were randomly assigned to one of three experimental conditions: 1) typical, in which they were simply sent home, 2) reading, in which they were asked to spend the next 20 minutes re-reading the feedback, and 3) recall, in which they were asked to spend the next 20 minutes writing down as much of the information from the feedback as they could remember. Two weeks following the intervention, participants completed a recall test and provided information on their alcohol use during the previous two weeks. Results indicated that participants in the reading and recall conditions retained more of the feedback information than did participants in the typical condition. In addition, participants in the reading and recall conditions reported reduced alcohol consumption in the two-week period following the intervention, compared to those in the typical condition. Information retention partially mediated the effects of the reading and recall conditions on drinking outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

PRACTICE GREEN ENGINEERING,KEEP THE JUNKYARDS CLEAR

This paper discusses the fracture prevention aspects of lifetime prediction. Initially, it is pointed out that lifetime can be determined by factors such as obsolescence and consumer rejection. Lifetime is then related to acceptable risk in order to make it compatible with advances in design philosophy for large welded structures. Accident statistics are cited and the argument made that the major opportunities for lifetime improvement are revealed by failure analysis, and are shown to lie in design and production. However, there are some structures, e.g. boilers and pressure vessels, where the construction rules are so well established that failures occur mainly because of operational errors. Based on the results of the Battelle/NBS Cost of Fracture Study, attention is focused on the effect of material–property reproducibility in driving failure probability. Little evidence could be found regarding reproducibility improvements of fatigue lifetime and brittle fracture toughness in production lots of alloys over time.     

Educating school psychologists to work with bilingual/bicultural populations.

Describes a university 66-credit professional diploma sequence that includes 1 yr of internship experience for the training of school psychologists to work with bilingual/bicultural populations. Competence for working with these populations involves 3 general areas: language, cross-cultural expertise, and assessment. An integrated curriculum and faculty offers linguistics, cultural-urban studies, and bilingual education courses in addition to the core courses in professional school psychology. Bilingual students and faculty have been recruited. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Microstructure of a quenched and tempered Cu-bearing high-strength low-alloy steel

The grain structure, inclusion content, and precipitate types were characterized for six heat treatments of a copper-bearing HSLA steel. A higher austenitizing temperature combined with water-quenching resulted in an acicular ferrite microstructure, while lower temperatures produced equiaxed ferrite or ferrite-pearlite structures. Refinement of equiaxed ferrite was observed in material austenitized at a high enough temperature to dissolve a portion of the carbonitrides, allowing reprecipitation during the austenite-ferrite transformation. Age-hardening precipitated body-centered cubic copper clusters; face-centered cubic copper precipitates were observed in overaged material.