Chevron markings

These weld defects not only substantially reduced the mechanical strength of the weld, the pores also formed stress-concentrating notches. Consequently, when the door frame was inadvertently struck during the scrap charging operation, a fracture initiated at the deficient weld and propagated rapidly through the %-in. (1.9-cm) plate, as revealed by the brittle appearance of the plate fracture and the directional chevron markings. 

Theories of the oxidation of tantalum in the presence of suboxide have been developed by Stringer. By means of single-crystal studies he has been able to show that a rate anisotropy stems from the orientation of the suboxide which is precipitated in the form of thin plates. Their influence on the oxidation rate is least when they lie parallel to the metal interface, since the stresses set up by their oxidation to the pentoxide are most easily accommodated. By contrast, when the plates are at 45° to the surface, complex stresses are established which create characteristic chevron markings and cracks in the oxide. The cracks in this case follow lines of pores generated by oxidation of the plates. This behaviour is also found with niobium, but surprisingly, these pores are not formed when Ta-Nb alloys are oxidised, and the rate anisotropy disappears. However, the rate remains linear it seems that this is another case in which molecular oxygen travels by sub-microscopic routes. 

Zone 2E - Rapid crack growth zone, with terraced or chevron markings. 

Chevron markings are predominant in zones 2B, 2D and 2E and they suggest that the mechanism of fracture is similar in these sub-zones. 

Studies reveal a statistically significant reduction in accidents of 56% on and near the chevron markings at two sites on the Ml. 

Two Countermeasures to Influence Driver Behaviour in Fog (A16 Fog-Signalling System and A59 Chevron Markings)... 

Another countermeasure to improve driving behaviour in fog is chevron markings painted on the roadway surface, for example, like those on the A59 motorway... 

From both studies it was concluded that large-scale implementation of chevron markings is not recommended as drivers adapted their behaviour by driving faster in some conditions (Hogema et al., 1993) and by detecting a lead vehicle more slowly (van der Horst and Hoekstra, 1993) with negative consequences on safety. 

Horst, A.R.A. van der, and Hoekstra, W. 1993. Het waamemen van chevronstrepen bij mist Een simulatorstudie [The perception of chevron markings in fog A simulator study] (Report IZF 1993 C-10). Soesterberg TNO Institute for Perception. 

Figure 8.5 (a) Photograph showing V-shaped chevron markings characteristic of brittle fracture. Arrows... 

Figure 8.23 (b) Confocal laser scanning microscopy image of potassium hydrogen phthalate with occluded dichlorofluorecein showing details of luminescence that has developed in the fast growing slopes of the (010) growth hillock. The vertices of the chevron-shaped hillock fossils mark dislocation cores (reproduced by permission of The Royal Society of Chemistry). 

Figure 3.12 Schematic drawing of the morphology of a multilayer system with sticks of parallel lamellae in different orientations (globally unoriented system) before deformation (left) and after deformation (right for deformation direction see arrow) chevron formation appears in a lamellar block marked as A ...

NE Upgrading guardrail Providing the proper superelevation New pavement marking/delineators/chevrons Milled rumble strips Surfaced turnouts for mailboxes... 

Curve deline ation/waming (pavement markings and chevrons). 

A fractographic pattern of radial marks (shear ledges) that look like nested letter V s sometimes called a herringbone pattern. Chevron patterns are typically found on brittle fracture surfaces in parts whose widths are considerably greater than their thicknesses. The points of the chevrons can be traced back to the fracture origin. 

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