(2) Examine windowpanes for routed radius crazing.
(a)
Crazing in the radius of the routed edge (Fig. 603) of an outer pane is more serious than that in the overall surface. As the point of crazing moves around the radius towards the outside surface of the pane so the seriousness of the defect decreases. This is due to a falling off in stress levels to the point where, at the intersection of the outside contour with the routed edge, there is very little stress.
(b)
The routed edge of the windowpane is the most likely part in which crazing may occur. The routed edge, being that part of the pane nearest the surrounding structure, is more prone to contamination with cleaning solvents and other undesirable materials when window is inadequately masked during cleaning or painting. The contamination material could seep down into the gap between the pane and the window frame forging where the outer pane peripheral seal might aggravate the situation by soaking up the material and prolonging contact. Also, the routed radius unavoidably constitutes a stress raiser, especially since it is adjacent to the supporting forging and is at a point of near maximum shear transfer.
H30522
Method of Measuring Depth of Crazing 500
56-22-0 Figure 602 Feb 20/89
Page 604
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(c)
The routed radius can be checked for crazing without having to remove the pane; it can be checked from the inside. If examination of the windowpanes is done on a sampling basis, some windows will have crazed routed radii and will not get checked. However, stretched acrylic has the quality of restraining craze propagation and will probably last until the next overhaul. If crazing is evident in the routed radius above the limits mentioned in par. (d), that pane should be replaced and remaining windows examined.
(d)
Crazing around the routed radius and routed edge may be more or less continuous in which case the maximum depth of penetration shall be 0.025 inch. Crazing around delaminated areas shall not exceed 0.010 inch deep.
H30524
500 Joint of Acrylic Pane with Window Frame Forging
Feb 20/89 Figure 603 56-22-0
Page 605
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(3)
Examine windowpanes for in-plane cracking (formerly identified as delamination).
(a)
The stretching process used in the acrylic pane manufacture results in a lower shear strength parallel to the pane surface than that perpendicular to the surface. Because of this the acrylic behaves, in many ways, like a multilayer laminate. In-plane cracking is a separation of adjacent layers parallel to the pane surface. It can be induced by a blow with a sharp instrument on the pane edge and usually accompanies deep penetrations into the pane surface. For clarity, fine continuous in-plane cracking is defined as crazing.
CAUTION: NO IN-PLANE CRACKING IS ALLOWED IN THE CENTER PANE.
(b)
Outer pane in-plane cracking at the extreme edge (Fig. 603) is permissible within the following limits: 1) Maximum extension in from edge 0.40 inch 2) Maximum length at edge 1.00 inch 3) Minimum distance between defects 2.00 inches 4) Maximum number per edge 2 5) Maximum number per pane 4
(c)
Large in-plane cracks in the routed radius are definitely more serious than crazing at the same place. This is because the stretching process of manufacture decreases the ability of the acrylic to resist spreading of in-plane cracking, parallel to the direction of stretching.
(d)
A routed radius in-plane crack will probably not occur as often as a crazing defect in the same place. Whereas the rubber peripheral seal on the outer pane tended to aggravate the crazing, it now serves as a protective bumper against sharp blows on the radius producing in-plane cracking. Should evidence of routed radius in-plane cracking be found, the window frame forging should be examined for sharp protrusions and the general fit of the pane in the forging examined.
(e)
In-plane cracking around the routed edge and routed radius may be continuous and the maximum depth of penetration shall be 0.025 inch. For localized in-plane cracking in the routed radius and routed edge, one local area per side of windowpane may have a maximum depth of penetration of 0.05 inch with a maximum length of
0.50 inch provided the crazing around the in-plane cracked area does not exceed
0.010 deep.
(f)
In-plane cracking of the outer pane, at any place other than the edges, is often accompanied by chipping especially in the case of a blow with a blunt object. In the case of penetration by a sharp object, the in-plane cracking takes the form of a circle concentric with the hole. In-plane cracking and chips are permissible within the following limits: 1) Maximum chip depth 0.05 inch 2) Maximim size of in-plane crack 0.50-inch diameter 3) Minimum distance between defects Twice maximum damage diameter
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