The ratcheting behavior of a unidirectional carbon/epoxy laminate under off-axis cyclic loading conditions at high temperature has been studied with emphasis on its dependence on load waveform and fiber orientation. Development of an engineering model for describing the off-axis ratcheting deformation in the unidirectional CFRP laminate has also been attempted. First, off-axis ratcheting tests with different levels of maximum and non-zero mean stresses were performed on coupon specimens with different fiber orientations. The experimental results showed that the accumulation of ratcheting strain occurs in the unidirectional CFRP laminate, regardless of the fiber orientation, and the off-axis ratcheting behavior is similar to the off-axis transient creep behavior in all aspects of its stress, time and fiber orientation dependence. It is shown that the proposed model allows adequately predicting the off-axis ratcheting behavior of the unidirectional CFRP laminate for different stress ratios as well as for different fiber orientations.
Purpose
This paper aims to describe a new process for suppressing the formation of orange peel, which is a polymer laser sintering (LS) process error.
Design/methodology/approach
The target for controlling the suppression of orange peel is securing the contact between the molten polymer and the surrounding powder. The authors set the powder bed temperature closer to the melting temperature than that for a typical LS. Alternatively, the authors use a low-power laser to irradiate the powder bed surrounding the parts being built. The surface finish of the built parts was evaluated using a three-dimensional scanner.
Findings
Both approaches were effective in suppressing orange peel. From the viewpoint of reusability of the used powder, the process that includes low-power laser irradiation is practical. The presence or absence of contact between the surrounding powder and the molten polymer determines whether the orange peel is formed.
Research limitations/implications
The authors have not tested orange peel suppression for complex shapes.
Originality/value
The authors have demonstrated a concrete process that can suppress orange peel formation even for powders with low melt-flow rates. Furthermore, a mechanism for the formation/suppression of orange peel based on the experimental results was proposed.
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