Internal Stress Assessment of Thick-Section Injection-Mouldings

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Abstract
Ways of assessing internal stress in injection-moulded bars of thick cross-section (12.5 mm square), have been investigated. The layer removal procedure confirmed that residual stresses were tensile in the interior, but it was not possible to produce an accurate through-thickness stress profile. The Kubàt and Rigdahl analysis was found to give a satisfactory straight line extrapolation when applied to uniaxial compressive stress relaxation data, but the parameters so derived could not be correlated with the results of tensile tests. Birefringence measurements were made at various positions within the bars and some tentative deductions are discussed by reference to results obtained from thinner bars.