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TECHNOLOGY 35
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used to calculate the rotational stiffness of the joint. were assigned the material properties of fully dense RePLA+.
The maximum bending moment was expressed as the The sparse cubic infill was not modelled explicitly, but
product of the maximum force and the joint arm length. was replaced by a homogenised continuum with effective
Rotational stiffness was calculated from the change in bending properties dependent on the nominal infill density.
moment divided by the change in joint rotation angle within This modelling approach was adopted because the aim
the linear region. of the FEM analysis was not to reproduce the local behaviour

To evaluate material efficiency, the specific maximum of individual toolpaths, infill rib collapse, layer delamination,
bending moment was calculated as the maximum bending or filament-level damage.
moment divided by the nominal filament mass estimated by Instead, the model was intended for comparison of the
the slicing software for each connector configuration. global mechanical response, contact behaviour, and critical
The specimens were loaded at a constant crosshead stress regions of the connector configurations.
displacement rate of 10 mm/min. The maximum load was Replacing the sparse infill with a homogenised core reduced
defined as the highest force recorded during the test, and the computational cost and enabled comparison of variants
the post-peak failure criterion was defined as a decrease in with different infill densities without explicitly modelling the
force to 50 percent of the maximum load. internal infill geometry.

The experimental results were statistically analysed using a The effective density of the homogenised sparse infill was
two-way analysis of variance (ANOVA) to evaluate the influence calculated as the product of the fully dense material density
of infill density, perimeter count, and their interaction on the and the nominal infill density.
maximum bending moment, rotational stiffness, and specific The effective Young's modulus of the homogenised sparse
bending moment of the joints. infill was determined by simple scaling with relative density,
Statistical significance was assessed at ễ = 0.05. Model following the homogenisation concept used for FDM/FFF
residuals were assessed for normality using the Shapiro-Wilk parts with internal infill.

test, and homogeneity of variances was evaluated using The interfaces between the fully printed regions of the
Levene's test. FDM connector and the homogenised core were defined as
A FEM model was developed in ANSYS Mechanical to bonded contact, assuming perfect interaction between the
complement the experimental results and explain the load- connector domains without modelling delamination, toolpath
transfer mechanism between the FDM-printed connector and
the wooden members.
pxhere.com
The FEM analysis was not intended to provide a precise
prediction of failure initiation, layer delamination, or local
damage within the printed material.

Instead, it was used as a comparative and interpretative
tool for evaluating contact behaviour, reaction forces, and the
distribution of stresses in critical regions of the joint.
In the FEM model, the FDM-printed connector was
represented by a two-domain shell-core model. The fully
printed regions, including the perimeter walls, top and bottom
solid layers, bridges, and slicer-generated solid infill regions,