Wear characteristics of cutting tool in brittle removal of a ductile meta in high-speed machining

The contact stress and heating effect between the cutting tool and workpiece in metal machining is symmetrical. However, the symmetry may be destroyed by changes in the workpiece material mechanical properties, such as ductility. The goal of this study is to reveal the wear characteristics of the cutting tool in machining a ductile metal with the cutting speed at which the metal is embrittled by the high-strain-rate-embrittle effect (HSREE). Orthogonal high-speed turning experiments were carried out. Pure iron type DT8 was cut at different cutting speeds, ranging from 1000 m/min to 9000 m/min. The shape and morphology of the chips obtained in the experiment were observed and analyzed by optical microscope and scanning electron microscope (SEM). Tool wear characteristics at different cutting speeds were observed. It shows that the pure iron becomes completely brittle when the cutting speed is higher than 8000 m/min. On the rake face, the coating of the cutting tool bursts apart and peels off. A matrix crack originates in the cutting edge or rake face and extends to the flank face of the cutting tool. The effects of HSREE on the tool wear is discussed. The findings of this study are helpful for choosing a suitable tool for brittle cutting of the ductile metal pure iron with very high cutting speed and solving the problems in machining due to its high ductility and high stickiness

Quantitative Proteomics Reveals Myosin and Actin as Promising Saliva Biomarkers for Distinguishing Pre-Malignant and Malignant Oral Lesions

Oral cancer survival rates increase significantly when it is detected and treated early. Unfortunately, clinicians now lack tests which easily and reliably distinguish pre-malignant oral lesions from those already transitioned to malignancy. A test for proteins, ones found in non-invasively-collected whole saliva and whose abundances distinguish these lesion types, would meet this critical need.To discover such proteins, in a first-of-its-kind study we used advanced mass spectrometry-based quantitative proteomics analysis of the pooled soluble fraction of whole saliva from four subjects with pre-malignant lesions and four with malignant lesions. We prioritized candidate biomarkers via bioinformatics and validated selected proteins by western blotting. Bioinformatic analysis of differentially abundant proteins and initial western blotting revealed increased abundance of myosin and actin in patients with malignant lesions. We validated those results by additional western blotting of individual whole saliva samples from twelve other subjects with pre-malignant oral lesions and twelve with malignant oral lesions. Sensitivity/specificity values for distinguishing between different lesion types were 100%/75% (p = 0.002) for actin, and 67%/83% (p<0.00001) for myosin in soluble saliva. Exfoliated epithelial cells from subjects' saliva also showed increased myosin and actin abundance in those with malignant lesions, linking our observations in soluble saliva to abundance differences between pre-malignant and malignant cells.Salivary actin and myosin abundances distinguish oral lesion types with sensitivity and specificity rivaling other non-invasive oral cancer tests. Our findings provide a promising starting point for the development of non-invasive and inexpensive salivary tests to reliably detect oral cancer early

Indentation resistance of brittle auxetic structures : combining discrete representation and continuum model

This work investigates the indentation resistance of the auxetic/non-auxetic honeycomb ceramics layer by combining a discrete numerical representation and a continuum analytical model. The indentation depth of honeycombs with varying cell-wall angle and cell-wall thickness are measured. The indentation depth of auxetic honeycombs with negative Poisson's ratio (NPR) is smaller than that of conventional ones in the premise of the same cell-wall thickness. But on the condition that the honeycombs possess the same relative density, there exists an inverse tendency. The corresponding mechanisms responsible for those trends are revealed. The stress intensity factor (SIF) is defined to characterize the stress singularity at the corner of the punch. The influence of NPR on the magnitudes of SIF is evaluated. A punch toughness concept is defined by a novel multi-scale method as the failure criterion of brittle honeycomb ceramics in indentation tests. The effects of NPR on the punch toughness of honeycombs are discussed. And the empirical formulas of punch toughness varying with the cell-wall thickness and the relative density are summarized. Finally, the NPR effects on the collinear punches problem are detected; the results show that the auxetic performance can significantly weaken the interaction between the punches

Endemic fossil seed plants from China and a reassessment of coniferophyte phylogeny

Recent palaeobotanical studies have provided new and important evidence on Chinese fossil plants. The majority of these fossils are distinct from fossil floras known from other geographical regions. However, remarkably few of these fossil plants have been successfully incorporated into cladistic analyses, to assess their importance on evolutionary relationships among major plant groups. For the first time our investigation incorporates three endemic Chinese fossil plant species into a cladistic analysis of the seed plants. These plants have been documented and reconstructed in detailed investigations of Palaeozoic coal balls from the Taiyuan Formation and are named Shanxioxylon sinensis, Shanxioxylon taiyuanensis and Pennsylvanioxylon tianii respectively. Previous investigations indicate that these plants belong to the now extinct Cordaitalean seed plants although they share many features with certain fossil conifers. As such, they are likely to be of significance to the ongoing and currently unresolved debate concerning coniferophyte phylogeny.</p

Endemic fossil seed plants from China and a reassessment of coniferophyte phylogeny

Recent palaeobotanical studies have provided new and important evidence on Chinese fossil plants. The majority of these fossils are distinct from fossil floras known from other geographical regions. However, remarkably few of these fossil plants have been successfully incorporated into cladistic analyses, to assess their importance on evolutionary relationships among major plant groups. For the first time our investigation incorporates three endemic Chinese fossil plant species into a cladistic analysis of the seed plants. These plants have been documented and reconstructed in detailed investigations of Palaeozoic coal balls from the Taiyuan Formation and are named Shanxioxylon sinensis, Shanxioxylon taiyuanensis and Pennsylvanioxylon tianii respectively. Previous investigations indicate that these plants belong to the now extinct Cordaitalean seed plants although they share many features with certain fossil conifers. As such, they are likely to be of significance to the ongoing and currently unresolved debate concerning coniferophyte phylogeny.</p

The thermal shock resistance prediction of porous ceramic sandwich structures with temperature-dependent material properties

A general numerical model to predict the thermal shock resistance of porous ceramic sandwich (PCS) structures with temperature-dependent material properties is developed. Knowledge of the temperature distribution and associated thermal stress in PCS panel is determined by the finite element method of coupled thermoelasticity. The present work considers the hot/cold shock induced center/edge cracks and measures the time-varied thermal stress intensity factors at the crack tip area. The roles of crack length, relative density of foam core, thermal shock load and geometric parameters of the PCS structures are examined. Moreover, fracture failure analysis of the whole PCS structures is carried out and crack propagation manners are detected. The thermal shock resistance curves of the structures are provided and the critical thermal shock temperatures are estimated for any selected characteristic materials. Results reveal that the thermal shock resistance of the PCS structures will be dramatically underestimated with the ignorance of temperature-dependent material properties. The analysis model of this paper provides a rapid prediction of thermal shock behavior of PCS structures at arbitrary temperatures

A multi-scale model for predicting the thermal shock resistance of porous ceramics with temperature-dependent material properties

This paper develops a novel multi-scale thermal/mechanical analysis model which not only can efficiently measure the thermal shock response but also highly reflects the effects of diversiform micro-structures of porous ceramics. Knowledge of the temperature distribution and time-varied thermal stress intensity factors (SIF) is derived by finite element/finite difference method and the weight function method in the macro continuum model. The finite element analysis employs a micro-mechanical model in conjunction with the macro model for the purpose of relating the SIF to the thermal stress in the struts of the porous ceramics. The micro model around the crack tip was established by using Voronoi lattices to accurately explore the micro-architectural features of porous ceramics. Hot shock induced center crack and cold shock induced edge crack are both considered. Effects of relative density and pore size on the thermal shock resistance are investigated and the results are well coincident with the experimental tests. The influence of cell regularity and cross section shape of the cell struts is discussed and the corresponding explanations are provided. The importance of incorporating temperature-dependent material properties on the thermal shock resistance prediction is quantitatively represented. These multi-faceted models and results provide a significant guide to the design and selection of porous ceramics against the thermal shock fracture failure for the future thermal protection system of space shuttle

Crack branching and deflection in AISI 4340 steel under cyclic torsional loading

The high-cycle torsional fatigue crack propagation behaviors of the martensitic AISI 4340 steel were investigated in this work. Quantitative analyses of fracture processes were conducted to establish the branching mechanisms in the early crack propagation stage and the deflection in the later crack propagation stage. It was found that when the mode I stress intensity factor was greater than the threshold value KI,th, the initiated crack would branch off to four cracks in mode I. Furthermore, there is a competitive relationship among different pairs of branches. Firstly, the backward pair of branches encountered more boundary barriers. Secondly, their driving force was reduced by the stress redistribution caused by the leading pair of branches. In addition, due to the restriction of the grips, the crack would gradually turn into mode II from mode I. When KII/KI &gt; 1.5, the cracks growth type became complete mode II

Improving thermomechanical properties of cracked brittle honeycombs by negative Poisson's ratio effect

This work investigates the effects of cracking on the overall properties of brittle auxetic/non-auxetic honeycombs. The micro numerical model and macro theoretical model are established simultaneously. The analytical expressions of crack opening displacement (COD) are derived and the results agree well with numerical simulations. The fracture toughness of honeycombs is calculated by combining the stress in the numerical model and the stress intensity factor (SIF) in the theoretical model. The reductions in the equivalent stiffness and equivalent thermal stress coefficient (TSC) of the cracked honeycombs are predicted. The negative Poisson's ratio (NPR) effects on those fracture mechanics parameters and equivalent thermomechanical properties are studied. And considering the orthogonal anisotropic properties of honeycombs, the cracking along two orthogonal directions is examined. It reveals that the significant NPR effects can only be detected in a single direction and the effects in another direction are inconspicuous. In addition, the effects of crack length, medium dimensions, and cell-wall angle of honeycomb cells on the overall performance of the cracked medium are also evaluated by parametric studies and the results are displayed graphically