Cracks can occur in the composite structures during production, assembly, or usage. Environment temperature, deformation rate, and crack geometry have a direct influence on the fracture behavior of laminated composites. In this study, the fracture behavior of S-2 glass/epoxy composites having different crack geometry at different temperatures and deformation rates was investigated experimentally and numerically. Within the scope of the study, the fracture toughness (K) and strain energy release rate (G) values of samples with 5 mm crack geometry were calculated for the crack tip opening conditions in Mode I and Mode I/II. Fracture tests at different environmental temperatures were performed to investigate the effects of temperature on fracture behavior. Fracture tests were achieved at three different deformation rates, to exhibit the relationship between crack initiation and deformation rate. Also, the fracture behavior of S-2 glass/epoxy laminated composites was analyzed by using the finite element method (FEM). S-2 glass fabric reinforced composite is used as a new alternative to traditional building materials, especially in the aviation, space and military industries. The results obtained from the experimental and FEM studies of this composite structure showed that different environmental and loading conditions were effective on the fracture behavior of the composite structure.

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Bu çalışmada, fiber takviyeli kompozit levhalar, ahşap levhalar, plastik esaslı levhalar ve hafif metalik levhaların eğilmeli yorulma davranışlarını karakterize eden özgün bir yorulma test makinesi geliştirilmiştir. Geliştirilen özel bilgisayar yazılımı ile kontrol edilebilen ankastre-tip eğilmeli test makinesi, yorulma testi için deplasman kontrol metodunu kullanmaktadır. Yorulma testleri uzun süren mekanik testlerdendir. Geliştirilen test makinesi aynı anda 10 numuneyi test edebilme özelliği sayesinde zamandan ve enerjiden tasarruf edilebilmektedir. Yazılım ara yüzü üzerinden yapılacak basit veri girişleri ile farklı sehim oranları (R) ve 0.1-10 Hz frekans altında yorulma testleri yapılabilmektedir. Her bir numune için test zamanı, test frekansı, eğme kuvveti, rijitlik kaybı, yük tekrar sayısı gibi parametreler hem yazılım ara yüzünden hem de internet üzerinden izlenebilmektedir ve müdahale edilebilmektedir. Numunelerinden herhangi biri hasara uğradığında araştırmacının e-postasına uyarı mesajı ve ilgili test verilerini gönderebilmektedir. Performans ve kalibrasyon için yapılan eğilme testlerinden elde edilen sonuçların, literatürdeki benzerleri ile uyumlu olduğu gözlemlenmiştir.

Fiber-reinforced laminated composite is often used in harsh environments that may affect their static stability and long-term durability as well as residual strength. In this study, the effect of heavy chemical environments such as acid and alkaline and retaining time for these environments on flexural strength and flexural fatigue behavior of carbon/epoxy laminated composites were investigated. In this context, carbon/epoxy was retained into an acidic and alkaline solution having 5%, 15%, and 25% concentration by weight for 1–4 months. Fatigue behavior of carbon/epoxy was determined under dynamic flexural load, which corresponds to 80%, 70%, 60%, 50%, and 40% of static three-point bending strength of the test sample. SEM image of damaged specimens was taken to describe the failure mechanism of damage which occurs after fatigue. Also, to better understand environmental condition on the fatigue life, results were compared with results of carbon/epoxy laminated composites, which were not retained into any environments (unretained). The test results showed that the solution type, solution concentration, and retaining time caused noticeable changes in the static and dynamic strengths of carbon/epoxy laminated composites.