Experimental and Numerical Studies on Tensile and Shear Fracturing of Brittle Materials

Öz

Sudden and violent fracturing of brittle materials, such as rocks and concretes, still remain one of the leading causes of fatalities in mining, civil and geotechnical industries today. The primary aim of this study is to investigate the mixed modes, mode I (tensile) and mode II (shearing) fracturing mechanisms of rock and prepared concrete specimens using Crack Chevron Notched Brazillian Disc (CCNBD) specimen geometries. Static diametrical compression tests showed that the notched cracks at the centre of the specimens opened (Mode I) up to 30 crack inclination angle (β), whereas crack closure started for β > 33, and closure became more pronounced at even higher β of 45 and 70. A series of numerical analyses were then performed by using a Finite Element Method (FEM) software FRANC2D to simulate the stress distributions and fracturing behaviour of the samples at different β, and to obtain the Mode I and Mode II fracture toughness values KIc and KIIc respectively. According to the numerical results, it was unlikely to obtain pure Modes I and II using both the CCNBD specimens under diametral compressive loading. Furthermore, the numerical simulations also suggested that KIc was more effective on crack initiation than KIIc; whereas, at the onset of crack propagation, the opposite was the case.

Anahtar Kelimeler

• Fracture toughness,Mode I and Mode II fracturing,FRANC2D,Fracturing of rock and concrete

Kırılgan Malzemelerin Çekme ve Makaslama Kırılmaları Üzerinde Deneysel ve Sayısal Çalışmalar

Öz

Kayalar ve beton gibi kırılgan malzemelerin ani ve şiddetli kırılmaları hala madencilik ve inşaat endüstrilerinde ölümcül olayların sebepleridir. Bu çalışmanın temel amacı ortak kırılma modu olan modeI-II, mod I (çekme kırılmaları) ve mod II (makaslama) kırılmalarından oluşan yenilmelerin, hazırlanmış CCNBD ismi verilen kaya ve beton numuneler ile incelenmesidir. Statik çapsal basma gerilmesi altında test edilen numunelerde, çatlak eğim açısı , 30 olana kadar çentik çatlağında Mod I kırılmaya neden olan açılmalar görülmüştür. Bunun yanında  açısı 33’den büyük olduğunda ise çentik çatlağında kapanma gözlenmiştir ve bu kapanma  açısı 45 ve 70 olduğunda oldukça fazla ve belirgin olmuştur. Sonlu elemanlar yöntemi ile işleyen FRANC2D programı kullanarak sayısal modellemeler yapılmıştır ve gerilme dağılımı analizi, çatlaklanma modellemeleri yapılarak Mod I ve II tıkızlık değerleri olan KIc and KIIc değerleri bulunmuştur. Sayısal analiz sonuçlarına göre, çapsal basma gerilmesi altında test edilen CCNBD numunelerde salt Mod I veya salt Mod II kırılmaların mümkün olmadığı bulunmuştur. Ayrıca sayısal analiz sonuçları, çatlaklanmanın başlamasında mode I tıkızlık değeri olan KIC’nin Mod II tıkızlık değeri KIIC’den daha baskın olduğu ve oluşmuş çatlağın ilerlemesinde ise tam tersi olduğunu göstermiştir.

Anahtar Kelimeler

• Kırılma tıkızlığı,Mod I ve Mod II kırılma,FRANC2D,Kaya ve beton kırılmaları

Kaynakça

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