Yazar "Ulus, Hasan" seçeneğine göre listele

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    Öğe
    Coupled Dimensional Energy Balance and Machine Learning Validation for Ballistic Response Prediction of Fiber Composites
    (Korean Fiber Soc, 2025) Beylergil, Bertan; Ulus, Hasan; Yildiz, Mehmet
    In this study, we present a coupled, dimensional energy-balance model enhanced with machine-learning validation to predict residual-velocity curves and ballistic limits of fiber-reinforced composites. Projectile deceleration is described as a three-term balance involving strength-like, drag-like, and inertial effects, mapped to the nondimensional groups Pi(0), Pi(1), and Pi(2); closed-form and RK4 solutions yield residual velocity and regime boundaries (Pi(0) = Pi(1), Pi(1) = Pi(2)). Validation against six literature datasets (CFRP and aramid laminates; Vr-V0 curves) shows high accuracy: median R2 = 0.93-0.96 and typical RMSE = 10-30 ms(-)1, with best case R2 = 0.976 and RMSE = 6.99 ms(-)1 for thin CFRP. Ballistic-limit predictions accurately capture the nonlinear increase with thickness, with errors less than 1 ms(-)1 in brittle CFRP and up to 10 ms(-)1 in Kevlar laminates. A global master curve of wr = Vr/V0 versus parallel to Pi parallel to 2 collapses all data and shows a consistent trend. Energy-budget analysis quantifies the contributions of the three terms: the strength term Pi(0) dominates in about 90% of operational points, while drag-like effects are minimal and inertial effects only appear at thick or high-velocity limits; the dominance fractions and combined contributions support these shifts. The (V-0,h) regime map, derived by setting Pi(0) = Pi(1) and Pi(1) = Pi(2), separates design-relevant domains and aligns with observed transitions in Vr-V0 modes and slopes. An independent machine-learning check using Random Forests achieves R2 = 0.992, RMSE = 17.5 ms(-)1, and MAE = 12.4 ms(-)1 (fivefold cross-validation: R2 = 0.835 +/- 0.145), supporting the mechanistic hierarchy through feature importance. The integrated physics-based model and machine-learning analysis provide traceable parameters (alpha, beta, gamma), uncertainty bounds, and practical screening maps for composite and geometric options under high-velocity impact.
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    Öğe
    Effect of atmospheric plasma treatment on Mode-I and Mode-II fracture toughness properties of adhesively bonded carbon fiber/PEKK composite joints
    (Pergamon-Elsevier Science Ltd, 2023) Yildirim, Ceren; Ulus, Hasan; Beylergil, Bertan; Al-Nadhari, Abdulrahman; Topal, Serra; Yildiz, Mehmet
    This study aims to assess the influence of peel-ply (PP), mechanical abrasion (MA), and atmospheric plasma activation (APA) treatments on Mode-I and Mode-II fracture toughness of carbon fiber/ poly-ether-ketone-ketone (CF/PEKK) composite joints. A comprehensive examination of the topography and wettability of the adherend surfaces is conducted using various methods. The CF/PEKK adherends are produced through an automated fiber placement (AFP) process, and the CF/PEKK bonded joints are prepared using two different structural adhesive films, one of which has a lower strength, while the other has a higher strength. To evaluate their fracture toughness properties, double cantilever beam (DCB) and end-notched flexure (ENF) tests are carried out in accordance with ASTM standards. Acoustic emission sensors are used to monitor the test specimens during DCB tests, allowing for an in-depth evaluation of the failure modes and damage propagations in the joints. The results show that the GIC and GIIC values of the APA-treated CF/ PEKK bonded joints are remarkably higher than those of the untreated ones, with a range of improvement of 34.0-84.8 times and 7.5-17.4 times, respectively. Adhesive failure is the dominant failure mode on the surfaces of non-treated (NT) and PP samples, while cohesive failure is more prominent in those treated with MA and APA. The failure modes of the treated samples varied depending on the adhesive used, with APA-treated samples always exhibiting a cohesive failure. It is observed that the AE counts increase more slowly in APA-treated samples compared to MA-treated joints as delamination progresses more slowly with cohesive failure dominant, which leads to a lower release of AE energy.
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    Öğe
    Tailoring adherend surfaces for enhanced bonding in CF/PEKK composites: Comparative analysis of atmospheric plasma activation and conventional treatments
    (Elsevier Sci Ltd, 2024) Yildirim, Ceren; Ulus, Hasan; Beylergil, Bertan; Al-Nadhari, Abdulrahman; Topal, Serra; Yildiz, Mehmet
    Here, we propose the utilization of atmospheric plasma activation (APA), which outperforms peel-ply (PP) treatment and mechanical abrasion (MA) in achieving high-performance adhesively bonded carbon fiber/polyetherketoneketone (CF/PEKK) composites. This study covers several key aspects, including the chemical and morphological characterization of treated surfaces and mechanical performance assessments of single lap-joints (SLJs) under tensile and flexural loading conditions. In addition, in-situ acoustic emission (AE) monitoring is employed during tensile tests to determine dominant damage types and failure modes in the SLJs. Surface analysis shows that MA increases roughness, PP treatment decreases wettability, while APA enhances wettability by modifying the surface chemistry. Tensile and flexural tests reveal that APA-treated joints surpassed nontreated (NT) ones, with up to 5- and 7-times higher load-carrying performance, respectively, while fracture analysis suggests a shift from adhesive to cohesive failure. AE results show that increased AE events related to cohesive failure align with improved interface interactions.