The stresses within the tip of a pencil are examined theoretically, numerically, and experimentally to determine the position and orientation of the fracture surface. The von Mises stress is used to evaluate the impact of the normal and shear stresses due to compression, bending, torsion, and shear. The worst-case stress is shown to occur along the top edge of the inclined pencil point, where the normal stress is compressive. The resulting crack propagates diagonally downwards and towards the tip from this initial position, and is frequently observed to contain a cusp.
Issue Section:
Technical Briefs
1.
Cronquist
, D.
, 1979, “Broken Off Pencil Points
,” Am. J. Phys.
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, pp. 653
–655
.2.
Cowin
, S. C.
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,” J. Appl. Mech.
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, pp. 453
–454
.3.
Beer
, F.
, Johnston
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, and DeWolf
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, New York
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Gere
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, Boston, pp. 236
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.5.
Anderson
T. L.
, 1995, Fracture Mechanics: Fundamentals and Applications
, 2nd ed., CRC Press
, Boca Raton, FL.6.
Copyright © 2006
by American Society of Mechanical Engineers
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