Numerical and Experimental Investigation of Metallic Sandwich Panel Beams with Honeycomb Core Considering Damage and Repair Effects on Their Vibrational

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Numerical and Experimental Investigation of Metallic Sandwich Panel Beams with Honeycomb Core Considering Damage and Repair Effects on Their Vibrational

ارائه دهنده: Provider: Amir mirderikvandi

اساتید راهنما: Supervisors: Alireza Shushtari (Ph.D)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: (Ph.D)Hamed Kalhori(Ph.D) - Mehdi Karimi

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: 50

چکیده: Abstract: Abstract: Sandwich panels with honeycomb cores represent one of the most advanced engineering structures widely used in aerospace, automotive, and construction industries due to their excellent strength-to-weight ratio and structural efficiency. This thesis investigates the numerical and experimental behavior of metallic sandwich panel beams with honeycomb cores, with a particular focus on the effects of damage and subsequent repair on their vibrational characteristics. The primary motivation stems from practical challenges in the maintenance and repair of aerospace structures, where damages such as core crushing, face-sheet debonding, or local failure can significantly alter natural frequencies and mode shapes. These changes may lead to undesirable resonance amplification and reduced structural lifespan. Therefore, evaluating effective repair methods—such as epoxy adhesive bonding and patch repair—and comparing their performance with the intact (healthy) state is essential. The research adopts a mixed methodology combining numerical simulation and experimental testing. In the numerical part, the sandwich panel with approximate dimensions of 18.5 × 19.8 cm was modeled using ANSYS software. The face-sheets were made of 2024-T3 aluminum alloy with a thickness of 1 mm, while the honeycomb core was 5052 aluminums with a cell wall thickness of 0.1 mm and a hexagonal cell size of approximately 6 mm. For accurate representation of the periodic hexagonal cell structure, the core was meshed using the Sweep method with dominant hexahedral (Hex Dominant) elements. The upper and lower face-sheets were modeled with SHELL181 elements and meshed using the MultiZone Quad/Tri technique. A mesh convergence study was conducted by progressively refining the element size until frequency convergence was achieved (final element size of 6 mm). Additionally, the influence of core geometry variation (halving and doubling the cell size relative to the baseline) on vibrational behavior was examined, revealing that smaller cell sizes increase structural stiffness and natural frequencies. In the experimental phase, a real-scale sandwich panel specimen was fabricated and tested under free vibration conditions with one end clamped (cantilever configuration). Excitation was performed using an impact hammer, and responses were measured using accelerometers connected to a signal processing system. Damage was intentionally introduced as localized failure in the core and face-sheets. Two repair methods were then applied: (a) repair using reinforced epoxy adhesive, and (b) repair using an aluminum patch. The results demonstrated that the induced damage caused a significant reduction in natural frequencies (approximately 25–30% in the initial modes). Repair with epoxy adhesive partially recovered the frequencies (restoring about 70–80% of the intact-state values), whereas patch repair exhibited superior performance, bringing the frequencies closest to the healthy state (discrepancy less than 5–10% in most modes). This superior outcome is attributed to better stiffness recovery and more uniform stress distribution provided by the patch method. Comparison between numerical and experimental results confirmed the overall consistency of the observed trends. In conclusion, this study validates that patch repair outperforms adhesive bonding in restoring the vibrational behavior of damaged sandwich panels, making it a more reliable option for critical aerospace applications.