The fracture properties of molded articles containing weld‐lines are analyzed by a fracture mechanics approach, treating the weld‐line as a sharp crack. The theoretical length of the weld‐line crack is estimated from diffusion properties and a simple model of cooling in a mold. These estimated weld‐line crack lengths are found to be in excellent agreement with weld‐line crack lengths calculated from measured fracture properties. Above a critical melt temperature, this weld‐line crack length will fall below a critical crack length, whereby the weld‐line will no longer initiate brittle fracture. This critical crack length is a function of the material's inherent yield strength and fracture toughness. The embrittling effect of weld‐lines can also be easily removed by surface treatments such as surface milling or solvent polishing. Weld‐lines are, therefore, determined to be near‐surface flaws, which embrittle notch sensitive materials such as most amorphous polymers.
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Thomas J. Pecorini (1997) studied this question.
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