3 research outputs found
Damage and failure modelling of carbon and glass 2D braided composites
Composite materials have been increasingly used in the past two decades since they
offer significant potential weight reduction, part design flexibility and improved specific
mechanical performance compared to traditional metals. For specific applications, braid
reinforced composites offer better near net shape part and manufacturing flexibility than
conventional unidirectional laminates, albeit at the expense of slightly lower in-plane
stiffness and strength. Furthermore, for impact and crash applications, which is the
emphasis of this thesis, their tow waviness and interlocking can offer excellent damage
tolerance and energy absorption.
In this work, heavy tow (24k) biaxial carbon and glass braided preforms were used to
manufacture coupons and beam structures to undertake an extensive testing campaign to
characterise different damage and failure mechanisms occurring in braided composites.
Due to large shear deformation and surface degradation, non conventional measurement
techniques based on marker tracking and Digital Image Correlation were successfully
used to measure strains in the damaging material.
The modelling of braided composites was conducted using the meso-scale damage
approach first proposed by P. Ladevèze for unidirectional composites. The calibration
of an equivalent braid unidirectional ply was achieved using the experimental results
obtained for different braided coupons. Furthermore, failure mechanisms observed
experimentally, such as tow stretching and fibre re-orientation occurring during loading
history, were integrated into the model. A new unidirectional ply formulation was
subsequently implemented into the explicit finite element code PAM-CRASHTM.
Validation of the new model using single element, coupons and beams were conducted
that provided a satisfying correlation between experimental tests and numerical
predictions
Damage and failure modelling of carbon and glass 2D braided composites
Composite materials have been increasingly used in the past two decades since they offer significant potential weight reduction, part design flexibility and improved specific mechanical performance compared to traditional metals. For specific applications, braid reinforced composites offer better near net shape part and manufacturing flexibility than conventional unidirectional laminates, albeit at the expense of slightly lower in-plane stiffness and strength. Furthermore, for impact and crash applications, which is the emphasis of this thesis, their tow waviness and interlocking can offer excellent damage tolerance and energy absorption. In this work, heavy tow (24k) biaxial carbon and glass braided preforms were used to manufacture coupons and beam structures to undertake an extensive testing campaign to characterise different damage and failure mechanisms occurring in braided composites. Due to large shear deformation and surface degradation, non conventional measurement techniques based on marker tracking and Digital Image Correlation were successfully used to measure strains in the damaging material. The modelling of braided composites was conducted using the meso-scale damage approach first proposed by P. Ladevèze for unidirectional composites. The calibration of an equivalent braid unidirectional ply was achieved using the experimental results obtained for different braided coupons. Furthermore, failure mechanisms observed experimentally, such as tow stretching and fibre re-orientation occurring during loading history, were integrated into the model. A new unidirectional ply formulation was subsequently implemented into the explicit finite element code PAM-CRASHTM. Validation of the new model using single element, coupons and beams were conducted that provided a satisfying correlation between experimental tests and numerical predictions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Material characterisation and calibration of a meso-mechanical damage model for braid reinforced composites
Cost effective braid reinforced composites are a potential substitute for metals
in many automotive structural applications where good mechanical performance
combined with high energy absorption are of special interest. This paper
presents experimental work undertaken to characterise braided composites and a
meso-mechanical damage model suitable for the impact and crash analysis of
braided composites. The model presented correctly represents stiffness, initial
failure and the post failure damage response, which is of particular importance
for crash applications. Furthermore, work is presented that describes testing
procedures, which should be followed in order to obtain the correct material
parameters for analysis. Finally, validation of the testing procedures and the
constitutive model is made against a structural braid reinforced composite beam
loaded to failure under four point bending