Characterization of Damage and Adiabatic Heating in Advanced Fiber-Reinforced Polymers Under High Strain Rate Loading
Pournoori, Nazanin (2026)
Tampere University
2026
Teknisten tieteiden tohtoriohjelma - Doctoral Programme in Engineering Sciences
Yhteiskuntatieteiden tiedekunta - Faculty of Social Sciences
This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
Väitöspäivä
2026-01-30
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-03-4357-6
https://urn.fi/URN:ISBN:978-952-03-4357-6
Tiivistelmä
The understanding of the thermo-mechanical behavior of fiber-reinforced polymer (FRP) composites under dynamic loading is important for their effective application across various industries from aerospace and automotive to construction and infrastructure. Furthermore, the damage in various FRP laminates is influenced by strain rate, and the effects must be analyzed well to optimize structural performance and ensure reliability. While traditional test methods reliably measure deformation in isotropic materials, they often fail to determine the complex, anisotropic behavior of FRP composites, necessitating advanced techniques to accurately characterize mechanical response and damage evolution. This dissertation studies how a combination of experimental techniques and numerical simulations can enhance the characterization accuracy of damage and adiabatic heating in FRP composites at high strain rates. The work also aims to improve the understanding of the energy conversion processes and fracture toughness near the crack tip in laminated composites during high strain rate events.
A synchronized experimental setup, integrating high-speed infrared and optical imaging with digital image correlation (DIC), was used to simultaneously record real-time strain and temperature data during high strain rate loading of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) specimens. In addition, the damage evolution and final fracture pattern inside the specimen was studied using the in-situ ultra-high speed synchrotron X-ray phase contrast imaging (XPCI). The ultra-high speed imaging tracks the crack propagation through-thickness at a very high spatial resolution and timing scale of microseconds.
The in-situ experimental observations and finite element (FE) simulations were used to predict failure onset and evolution in GFRP and CFRP specimens at the length scale of individual plies at high strain rates. The location and mode of failure onset in GFRP at high strain rates were predicted using three-dimensional Hashin (3DH) failure criterion and strain rate-dependent elasticity. The crack propagation was modeled using the Virtual Crack Closure Technique (VCCT) based on the visually observed crack plane in the experiments to evaluate the energy dissipated by the crack tip. Furthermore, the experimental observations and FE simulations
were used to determine the fracture toughness and crack growth speed of high strain rate delamination. CFRP specimens with a new type of design were used to induce delamination. These specimens were tested with a Split Hopkinson Pressure Bar (SHPB) device, and the delamination was observed with the synchronized ultra-high speed XPCI. The experimentally observed location of the main delamination crack was used for FE simulations with the VCCT and, alternatively, with the Cohesive Zone Model (CZM) to analyze the critical energy release rate (ERR) at high strain rates. The FE simulations with the VCCT model were used to predict crack growth speed from the onset to full debonding, which is difficult to determine experimentally using XPCI or optical imaging techniques.
The results of this dissertation highlight the correlation between damage and heat generation in composite specimens under high strain rate loading. Simultaneous high-speed imaging of the GFRP and CFRP laminates reveals that the temperature starts to significantly increase by the onset of macroscopic damage at high strain rates. The damage onset occurs primarily due to matrix cracking at the interface of plies with different fiber orientations near the free edge. The maximum local temperatures in both CFRP and GFRP specimen tested at high strain rates were observed along the crack paths. The strain rate and loading direction with respect to the lay-up significantly influence the final fracture pattern and lead to different failure modes including fiber and matrix cracks, and fiber-matrix debonding. The 3DH failure criterion predicts the failure onset, location and mode. The in-situ XPCI measurements provide a detailed visualization of the crack onset and growth inside the newly designed CFRP specimen. The XPCI observations and FE simulations indicate that the delamination-related fracture toughness of the CFRP laminate decreases significantly at high strain rates. Future work will aim to develop coupled thermo-mechanical FE models to better predict energy dissipation and heat flux at the high strain rate delamination.
A synchronized experimental setup, integrating high-speed infrared and optical imaging with digital image correlation (DIC), was used to simultaneously record real-time strain and temperature data during high strain rate loading of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) specimens. In addition, the damage evolution and final fracture pattern inside the specimen was studied using the in-situ ultra-high speed synchrotron X-ray phase contrast imaging (XPCI). The ultra-high speed imaging tracks the crack propagation through-thickness at a very high spatial resolution and timing scale of microseconds.
The in-situ experimental observations and finite element (FE) simulations were used to predict failure onset and evolution in GFRP and CFRP specimens at the length scale of individual plies at high strain rates. The location and mode of failure onset in GFRP at high strain rates were predicted using three-dimensional Hashin (3DH) failure criterion and strain rate-dependent elasticity. The crack propagation was modeled using the Virtual Crack Closure Technique (VCCT) based on the visually observed crack plane in the experiments to evaluate the energy dissipated by the crack tip. Furthermore, the experimental observations and FE simulations
were used to determine the fracture toughness and crack growth speed of high strain rate delamination. CFRP specimens with a new type of design were used to induce delamination. These specimens were tested with a Split Hopkinson Pressure Bar (SHPB) device, and the delamination was observed with the synchronized ultra-high speed XPCI. The experimentally observed location of the main delamination crack was used for FE simulations with the VCCT and, alternatively, with the Cohesive Zone Model (CZM) to analyze the critical energy release rate (ERR) at high strain rates. The FE simulations with the VCCT model were used to predict crack growth speed from the onset to full debonding, which is difficult to determine experimentally using XPCI or optical imaging techniques.
The results of this dissertation highlight the correlation between damage and heat generation in composite specimens under high strain rate loading. Simultaneous high-speed imaging of the GFRP and CFRP laminates reveals that the temperature starts to significantly increase by the onset of macroscopic damage at high strain rates. The damage onset occurs primarily due to matrix cracking at the interface of plies with different fiber orientations near the free edge. The maximum local temperatures in both CFRP and GFRP specimen tested at high strain rates were observed along the crack paths. The strain rate and loading direction with respect to the lay-up significantly influence the final fracture pattern and lead to different failure modes including fiber and matrix cracks, and fiber-matrix debonding. The 3DH failure criterion predicts the failure onset, location and mode. The in-situ XPCI measurements provide a detailed visualization of the crack onset and growth inside the newly designed CFRP specimen. The XPCI observations and FE simulations indicate that the delamination-related fracture toughness of the CFRP laminate decreases significantly at high strain rates. Future work will aim to develop coupled thermo-mechanical FE models to better predict energy dissipation and heat flux at the high strain rate delamination.
Kokoelmat
- Väitöskirjat [5189]