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

Yıl 2017, Cilt: 32 Sayı: 2, 173 - 182, 15.06.2017

Nazife Erarslan

https://doi.org/10.21605/cukurovaummfd.358420

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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