Experimental and numerical investigation of damage process in composite laminates under low -velocity impact

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Havacılık ve Uzay Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2016

Öğrenci: ÖMER TANAY TOPAÇ

Eş Danışman: ERCAN GÜRSES, DEMİRKAN ÇÖKER

Özet:

Damage sensitivity of composites under out-of-plane dynamic loading, and its limited detectability on a structure has long remained a prominent problem in industry. In this study, simulations are compared with the real-time damage formation scheme, with the aim of increasing confidence in failure predictions. Drop-weight impact experiments are carried out on a [0/90]_s CFRP beam laminate. Initiation and progression of damage, consisting of matrix cracks and delamination, are visualized via ultra-high-speed camera at rates up to 60,000 fps and the sequence of failure events are captured. Evolution of dynamic strain fields is then quantified by a Digital Image Correlation (DIC) analysis and the resulting final failure patterns are characterized by a digital microscope. In the computational part, 3D finite element analysis is performed using ABAQUS/Explicit to simulate the experiments. Intraply matrix damage is modeled using a Continuum Damage Mechanics (CDM) based composite failure theory with LaRC04 initiation criterion and implemented via a user-written VUMAT subroutine. Delamination is modeled using cohesive interface elements introduced between 0°/90° interfaces. Damage initiation time, location and the interaction of failure modes and symmetry are compared with the experiments. The sequence of dynamic matrix cracking followed by dynamic delamination is observed for the first time. A good agreement between experimental and numerical results is achieved.