Finite element analysis of micro peel test for evaluating pulp fibre interfacial adhesion
Topic(s) : Material science
Co-authors :
Junaid ZUBAIR (FINLAND), Royson DSOUZA , Farzin JAVANSHOUR (FINLAND), Jarno JOKINEN (FINLAND), Pasi KALLIO (FINLAND), Essi SARLIN (FINLAND), Mikko KANERVA (FINLAND)Abstract :
Interfacial adhesion between reinforcing fibres and matrix in composite materials is challenging to determine due to the small dimensions, especially the diameter, of single fibres. There are extensive reviews [1] of possible micromechanical tests. One of the methods is the micro peel test [2,3]. The peel test is challenging for short and relatively weak fibres, such as natural fibres. However, in the peel test, it could be possible to control the fracture mode mixity during the testing by changing the fibre pulling angle by a sophisticated micro test device.
This work focuses on finite element method analysis for the micro peel test method to study the effects of fibre embedding angle (0…10 degrees) and pulling angle, i.e., load angle (45 and 90 degrees) on the interface stress state. Materials considered are 1) pulp fibre and the matrix substrate from 2) poly lactic acid (PLA). The model is implemented for Abaqus (standard) (see Figure 1) with 16 different geometries (models).
Young’s moduli were 50 GPa and 0.3145 GPa for a pulp fibre and PLA, respectively. Poisson’s ratios of 0.169 and 0.33 were applied for fibre and PLA, respectively. For plastic yield, limit of 60 MPa was set for PLA. For the interface model with cohesive zone modelling (CZM), cohesive stiffness was 1013 N/qm, critical traction (all modes) 10 MPa, and fracture toughness (all modes) 85 N/m.
The interface was studied for the regime of bond (see Figure 1) and the number and size of elements was precisely adjusted as constant as possible between the different geometries. A surface plot to see effects between the average von Mises stress, embedding angle, and load angle is shown in Figure 2. This plot shows the most interesting effects, i.e., that the influence of the embedding angle to the stress level can be seen for simulated load angle values. In details, the modelling of fibre exit (‘meniscus’) affects the results. The distribution and the behaviour with CZM are reported in the work.
For pulp fibres, to determine interfacial adhesion with the micro peel test, the load angle and embedding angle are expected to vary due to waviness and the challenging sample preparation with non-straight fibres. This work suggests that a load angle of 45 degrees can be beneficial to have more even stress level (-18…+22% difference to overall average) between samples of different embedding angle (0…10 degrees) compared to the 90 degrees load angle (-21…+77% difference to overall average). This result applies especially to strong interfaces, i.e., before crack onset.
Acknowledgements:
The authors want to acknowledge for collaboration the reserchers M. Kakkonen (Fibrobotics Oy), O. Tanhuanpaa (Fibrobotics Oy), T. Verho (VTT) and K. Immonen (VTT).
This work focuses on finite element method analysis for the micro peel test method to study the effects of fibre embedding angle (0…10 degrees) and pulling angle, i.e., load angle (45 and 90 degrees) on the interface stress state. Materials considered are 1) pulp fibre and the matrix substrate from 2) poly lactic acid (PLA). The model is implemented for Abaqus (standard) (see Figure 1) with 16 different geometries (models).
Young’s moduli were 50 GPa and 0.3145 GPa for a pulp fibre and PLA, respectively. Poisson’s ratios of 0.169 and 0.33 were applied for fibre and PLA, respectively. For plastic yield, limit of 60 MPa was set for PLA. For the interface model with cohesive zone modelling (CZM), cohesive stiffness was 1013 N/qm, critical traction (all modes) 10 MPa, and fracture toughness (all modes) 85 N/m.
The interface was studied for the regime of bond (see Figure 1) and the number and size of elements was precisely adjusted as constant as possible between the different geometries. A surface plot to see effects between the average von Mises stress, embedding angle, and load angle is shown in Figure 2. This plot shows the most interesting effects, i.e., that the influence of the embedding angle to the stress level can be seen for simulated load angle values. In details, the modelling of fibre exit (‘meniscus’) affects the results. The distribution and the behaviour with CZM are reported in the work.
For pulp fibres, to determine interfacial adhesion with the micro peel test, the load angle and embedding angle are expected to vary due to waviness and the challenging sample preparation with non-straight fibres. This work suggests that a load angle of 45 degrees can be beneficial to have more even stress level (-18…+22% difference to overall average) between samples of different embedding angle (0…10 degrees) compared to the 90 degrees load angle (-21…+77% difference to overall average). This result applies especially to strong interfaces, i.e., before crack onset.
Acknowledgements:
The authors want to acknowledge for collaboration the reserchers M. Kakkonen (Fibrobotics Oy), O. Tanhuanpaa (Fibrobotics Oy), T. Verho (VTT) and K. Immonen (VTT).