Search

Highlights • Spalling is a sub-surface induced rolling contact fatigue failure mode. • Increasing RA and decreasing sub-surface cracks at baseline condition can help to enhance macropitting or spalling life. • Baseline residual stress is less of a factor compared to RA content in impacting macropitting life. Abstract The objective of this study is to investigate the effect of retained austenite (RA) on the macropitting or spalling behavior of carburized AISI 8620 steel under boundary lubrication condition. Samples with RA ranging from approximately 0 to 70% were prepared using specific carburizing schemes. Macropitting tests were carried out at maximum contact pressure 1.9 GPa using a benchtop test rig. Samples were subsequently analyzed using noncontact white light profilometry and micro X-Ray Diffraction to observe the evolution of contact surface and RA respectively. Results indicated that increasing RA and minimizing pre-existing sub-surface cracks in the material help to enhance macropitting life. The failure mechanism for all samples was from spall formation due to sub-surface crack initiation and propagation with clear evidence of RA transforming to martensite. Pre- and post-experiment residual stress showed the impact of phase transformation on enhancement of residual stress during RCF experiments, however residual stress was not a significant factor in impacting the life. [ABSTRACT FROM AUTHOR]

Many newly manufactured components are subject to a run-in procedure. The objective of this study was to understand how the surface hardness of 16MnCr5 bearing steel evolved during running-in and how varying contact pressure and initial composite roughness affected this evolution. The evolution of the tribofilm formed by zinc dialkyl dithiophosphate (ZDDP) and how it contributed to the measured hardness was also analyzed. The results indicated a higher initial composite roughness led to greater gains in hardness as compared to higher contact pressure during the running-in process. Tribofilm growth appeared to have little to no significant effect on the measured surface hardness increase during running-in and the primary contributor to the observed hardness increase was work hardening. [ABSTRACT FROM AUTHOR]

In this study, the effect of different shielding gas and laser scanning velocity on the resulting retained austenite (RA) content and tribomechanical properties of AISI 8620 steel were investigated. RA generation was comparatively lower at higher scanning velocity and with argon as the shielding gas due to lower beam interaction time and inert environment. Varied heat input and differing reaction volume resulted in different hardness levels on these samples. Air shielded samples showed slightly higher friction coefficient than the other samples due to higher surface roughness and shearing of oxide layers. The nitrogen shielded samples exhibited the best wear resistance among all samples, which was attributed to nitride formation on surface and to high hardness resulting from the laser treatment. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cytonemes synapse with cells they target for signal exchange. [•] Signal exchange in cytoneme, axonal and dendritic synapses is analogous. [•] Contact-dependent signal exchange is not unique to neurons. [Copyright &y& Elsevier]

Many cellular processes in the dinoflagellate Lingulodinium polyedrum are controlled by a circadian (daily) clock. Since the activity of proteins involved in various metabolic pathways or in regulating gene expression can be affected by phosphorylation, we established a generalized phosphoproteome catalog using LC-MS/MS to analyze a phosphoprotein-enriched fraction. Over 11,000 peptides were identified by comparison to a Lingulodinium transcriptome, and 527 of these had at least one identified phosphosite. Gene ontology analysis revealed that RNA binding and translation were one of the major categories among these proteins identified by these peptides. Since casein kinase 2 (CK2) is known to be important in eukaryotic circadian biology substrates, we next tried to identify specific substrates for this kinase. To achieve this we first classified and catalogued the kinases in the Lingulodinium transcriptome then assigned the different phosphosites to the different kinase classes. Interestingly, potential CK2 targets include a substantial proportion of RNA binding proteins. Phosphosite identification thus provides a promising new approach to investigate the Lingulodinium circadian system. [ABSTRACT FROM AUTHOR]

Abstract: The cytokinetic protein FtsZ plays a pivotal role in regulation of cell division in bacteria. Multiple promoters regulate transcription of the ftsZ gene in Escherichia coli, Streptomyces and Bacillus species. In order to identify promoter activity-containing regions of the ftsZ gene of Mycobacterium tuberculosis H37Rv (MtftsZ) in vivo, different regions upstream of MtftsZ, namely, the ftsQ–ftsZ intergenic region, the ftsQ open reading frame (ORF), and different regions of ftsQ ORF, were analyzed in a gfp reporter plasmid in Mycobacterium smegmatis mc2155 cells. Flow cytometric analysis of mid-logarithmic M. smegmatis mc2155 cells containing these transcription fusion constructs revealed GFP expression in the cells harboring the ftsQ–ftsZ intergenic region (172 bp), the entire ftsQ ORF (945 bp), and 5′ 467-bp and 3′ 217-bp regions of ftsQ ORF. RT-PCR analyses on RNA from M. smegmatis mc2155 cells, transformed with the entire ftsQ ORF-ftsQ–ftsZ intergenic region-containing construct, as well as on RNA from M. tuberculosis, confirmed that the regions identified indeed elicit promoter activity. Semi-quantitative RT-PCR analyses of gfp transcripts driven by cloned MtftsZ promoter regions in M. smegmatis cells showed threefold higher promoter activity from ftsQ ORF than from the ftsQ–ftsZ intergenic region. Expression from the individual 5′ and 3′ regions of ftsQ ORF was almost equivalent to that from the ftsQ–ftsZ intergenic region. RT-PCR analyses on RNA from M. tuberculosis quantitatively confirmed these promoter activities. Thus, at least three independent regions in the immediate upstream sequence of MtftsZ contain promoter activity, with the major contribution coming from ftsQ ORF. [Copyright &y& Elsevier]

Enhancement of the fatigue resistance of welded transverse stiffeners and cover plate details by ultrasonic impact treatment (UIT) was evaluated in 18 full-scale W27×129 rolled beam specimens. Fatigue tests were conducted under constant amplitude loading at various stress range levels and at two minimum stress levels simulating the effect of sustained load. The test specimens were investigated for fatigue crack initiation and propagation. Distributions of residual stresses adjacent to the weld toe were determined before and after the treatment. Test results indicated that UIT enhanced the fatigue performance of all treated details by improving the weld toe profile, changing microstructure and introducing beneficial compressive residual stresses at the treated weld toe. The treatment effectively elevated the fatigue crack growth threshold and the fatigue limit without changing the slope of the S–N curve. [Copyright &y& Elsevier]

A phosphonium-phosphinate ionic liquid (IL) was studied as a lubricant additive for rolling-sliding contacts. The bench-scale test was designed to simulate automotive rear axle operation during cold start, highway towing, and overload conditions. Adding such an IL (2%) into a base oil significantly reduced wear loss and rolling contact fatigue, e.g., microcracking and micropitting, but made the vibrational noise notably higher under a low (−1.5%) sliding roll ratio (SRR). Worn surface characterization revealed an interesting texture pattern with alternating smoother plateaus and rougher valleys, which is believed to cause the high vibration. No increased vibration was observed at a high (−30%) SRR, possibly because the more aggressive sliding abrasion prevented such a surface texture from forming. • Unexpected behavior for a phosphonium phosphinate ionic liquid (IL) in rolling-sliding contact. • This IL provided effective wear and rolling contact fatigue protection but increased vibration. • Texture of alternating smoother plateaus and rougher valleys responsible for the high vibration. [ABSTRACT FROM AUTHOR]

High tensile weld residual stress is one important factor contributing to fatigue crack development even under reversal or compressive cyclic loadings. A compressive stress induced by post-weld treatment is beneficial by eliminating the tensile residual stresses and generating compressive residual stresses, which improves fatigue strength of welded structures. A study is underway to characterize the magnitude and subsurface distribution of residual stresses produced by post-weld treatments, particularly by Ultrasonic Impact Treatment (UIT), and to establish the post-weld treatment effect on fatigue resistance. Two post-weld treatments, UIT and shot peening, are involved in the present study. Internal stresses were investigated on three base metal samples treated by UIT and shot peening and on one welded sample treated by UIT through neutron diffraction and X-ray diffraction techniques. This paper presents the experimental conditions and the results of these stress measurements. It is revealed that the peak compressive residual stress induced by both treatments exceeded the yield stress of the base material near the sample surface. The depth of compressive stress layer in base metal was 1.5–1.7 mm for UIT and ~0.8 mm for shot peening. The induced compressive residual stresses benefit to increase the threshold value of stress intensity factor range, ΔKth, for fatigue crack initiation and early propagation. The effect of residual stresses modification on fatigue strength is discussed based on fracture mechanics model and verified by fatigue test results of large-scale welded beams. [Copyright &y& Elsevier]