A new modelling approach, using a combination of shell and solid elements, has been adopted to develop a realistic three-dimensional finite element (FE) model of the human scapula. Shell elements were used to represent a part of the compact bone layer (i.e. the outer cortical layer) and the very thin and rather flat part of the scapula--infraspinous fossa and supraspinous fossa respectively. Solid elements were used to model the remaining part of the compact bone and the trabecular bone. The FE model results in proper element shapes without distortion. The geometry, material properties and thickness were taken from quantitative computed tomography (CT) data. A thorough experimental set-up for strain gauge measurement on a fresh bone serves as a reference to assess the accuracy of FE predictions. A fresh cadaveric scapula with 18 strain gauges fixed at various locations and orientations was loaded in a mechanical testing machine and supported at three locations by linkage mechanisms interconnected by ball joints. This new experimental set-up was developed to impose bending and deflection of the scapula in all directions unambiguously, in response to applied loads at various locations. The measured strains (experimental) were compared to numerical (FE) strains, corresponding to several load cases, to validate the proposed FE modelling approach. Linear regression analysis was used to assess the accuracy of the results. The percentage error in the regression slope varies between 9 and 23 per cent. It appears, as a whole, that the two variables (measured and calculated strains) strongly depend on each other with a confidence level of more than 95 per cent. Considering the complicated testing procedure on a fresh sample of scapula, the high correlation coefficients (0.89-0.97), the low standard errors (29-105 micro epsilon) and percentage errors in the regression slope, as compared to other studies, strongly suggest that the strains calculated by the FE model can be used as a valid predictor of the actual measured strain. The model is therefore an alternative to a rigorous three-dimensional model based on solid elements only, which might often be too expensive in terms of computing time.

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Abstract. Thermoplastic composites with continuous fibres are attractive construction materials because of their good specific mechanical properties and their possibility to be processed very rapidly. An extremely fast processing method is folding of sheet material. Folding can be performed by local heating of a sheet along a line. Heating is done to a temperature, well above the softening or melting point of the thermoplastic polymer. Subsequent folding along the heated line requires very low forces. The folded geometry becomes permanent after cooling below the softening point of the polymer. Unfortunately, folding causes microbuckling of the reinforcing fibres at the compression side of the fold causing a severe reduction in the local strength. The present report describes a method for the folding of thermoplastic composites, which controls the direction of fibre microbuckling. The method results in a smaller strength reduction.The folding equipment is designed in such a way that microbuckling of the fibres occurs in a direction in the local plane of the sheet rather than being perpendicular to that plane. The result is a folded sheet with a reduction of about half of the original strength, as compared to a strength of only 15% of the original strength, which is typical for folds produced with more conventional means. In other words, the remaining strength is more then doubled using the new folding technology.

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