A novel measurement technique was developed to obtain unbiased fiber length distribution (FLD) measurements at specified locations in the thickness of the sample. This technique relies on elastic energy stored in long fiber thermoplastics (LFT), which is released during partially constrained burn-off. This release results in an increase of thickness dimension of the sample and partial disentanglement, allowing sample selection and subsequent filament separation. Quantitative FLD results and the measurement technique are discussed in detail. The FLD in long fiber reinforced injection molded thermoplastics is shown to vary as a function of thickness.
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