Role of plastic work in fatigue crack propagation in metals

The plastic work required for a unit area of fatigue crack propagation U was measured by cementing tiny foil strain gages ahead of propagating fatigue cracks and recording the stress-strain curves as the crack approached. Measurements of U and plastic zone size in aluminum alloys 2024-T4, 2219-T861, 2219 overaged, and A1-6.3 wt% Cu-T4, and a binary Ni-base alloy with 7.2 wt% A1 are herein reported. The results are discussed along with previously reported measurements of U in three steels and 7050 aluminum alloy. When U is compared to the fatigue crack propagation rate at constant ΔK along with strength and modulus, the conclusion is drawn that U is one of the parameters which determines the rate of fatigue crack propagation. The relation of U to microstructure is also discussed. “Homogeneous” plastic deformation in the plastic zone ahead of the crack seems desirable.     

Fatigue behavior of a precipitation hardening Ni−Al−Cu medium carbon steel

The fatigue behavior of an Fe-0.3 wt pet C-4 wt pet Ni-1 wt pet Al-1 wt pet Cu precipitation hardening steel was investigated in three different heat treated conditions which give similar tensile strengths but different microstructures. One heat treatment produced a lightly tempered lath martensite having fine carbides and a high dislocation density. The other two heat treatments produced highly tempered martensite with coarse carbides, fine intermetallic precipitates and a relatively low dislocation density. The steel in the lightly tempered condition showed marked softening on strain cycling while the highly tempered conditions resulted in both hardening and softening. The lightly tempered structure had better low cycle fatigue resistance but the two highly tempered structures had better high cycle resistance. The dislocation substructure in the lightly tempered steel rearranges itself and accommodates plastic strain during cyclic deformation while the substructure in the highly tempered structures containing fine precipitates resists rearrangement. This difference is suggested as the reason for the differences in behavior. The three conditions show little variation in their resistance to fatigue crack propagation. However, the highly tempered, precipitate containing structures were much more resistant to fatigue crack initiation in notched specimens.     

Cues used by raters in the rating of temperament requirements of jobs.

Could word and phrase cues in job definitions be standardized to achieve homogeneous concepts and interrater agreement in the ratings of so-called "temperament" requirements of jobs? There were 3 stages in this series of studies: (a) A review of the literature yielded 14 traits arranged in 7 bipolar pairs and defined for use in the ratings. 50 jobs were rated by 7 raters according to these definitions. (b) Inexperienced and experienced analysts applied the rating devices. (c) The 12 revised trait definitions were applied to the rating of the 2nd sample of 50 jobs. 10 raters participated. Much improved rater agreement and reliability resulted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conclusion-drawing, communicator credibility, and anxiety as factors in opinion change.

Ss' attitudes toward biological warfare and position on the Taylor Manifest Anxiety Scale were assessed. 4 experimental groups then read an article on biological warfare. The articles differed in the source attributed to the article and in the explicitness of the conclusion regarding the effectiveness of biological warfare. Opinion change was greater for Ss in "explicit" groups, for Ss with high anxiety, and for Ss with high residual concern. No relationship was found between opinion change and expressed knowledge of communicator's position or credibility of source. 22 references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fatigue Crack initiation and microcrack growth in 2024-T4 and 2124-T4 aluminum alloys

A metallograph was mounted directly on a closed-loop electrohydraulic testing unit and initiation of fatigue cracks was directly observed on polished notches at magnifications up to 800 times in aluminum alloys 2024 and 2124 in the T-4 condition. The latter is a high purity version of 2024 and contains considerably fewer constituent particles. At high stresses on the notch surface the fatigue cracks initiated on coarse slip lines in both alloys. At low stresses almost all of the cracks in 2024 initiated in the matrix adjacent to constituent particles. In 2124 at low stresses 50 pct of the cracks initiated near constituent particles and 50 pct in the matrix not near constituent particles. The probability that a constituent particle in 2024 initiates a fatigue crack falls off very rapidly as the particle size decreases below 6 μm. Growth of microcracks is impeded by grain boundaries. This research was done at Northwestern University.     

A method for processing paraffin sections of multilayer cultured tissue

A simple and rapid method is described for processing histological preparations from multilayer cultures growing in plastic Petri dishes, A covering collodion film is utilized to remove the tissue from the plastic dish and transfer it onto a paper block prior to embedding in Paraplast. To avoid any disruption by the collodion of the plasticware, the cultured tissue is first immersed in a solution of collodion and absolute alcohol (1:1) and then covered with pure collodion. All steps are carried out in the cold. This procedure allows morphological, histochemical, immunofluorescent, and autoradiographic studies to be carried out on serial sections of cultured tissue.