Matrix cracking stress

Matrix cracks begin to propagate at the matrix cracking stress (51,60)... 

Different models were also used to obtain the matrix cracking stress (omu), with Blissett et al. (1997) using the classic Aveston et al. (1971) (ACK) analysis and Boccaccini (1998) using the model of Pagano and Kim (1994), which gives omu as ... 

Although the two approaches are very similar, the value of A Tc in Boccaccini s model does not depend on the interfacial shear strength t, as a result of the model chosen for the value of matrix cracking stress. Blissett et al. (1997) suggested that their method was valid for the UD material providing that some key parameters (interfacial shear stress, matrix fracture energy) were determined independently. 

Sc Characteristic fiber strength °rme Matrix cracking stress... 

Then, the two approaches (K and ) lead to the same steady-state matrix cracking stress. 

A lower bound to the matrix cracking stress, crmc, is then obtained by invoking Eqn. (24), such thatf58... 

This result for Kttp, when combined with Eqn. (32), gives a revised matrix cracking stress, which exceeds omc. 

Fig. 1.6) indicates that the matrix has a major influence on the shear flow strength ts and the shear ductility, yc. Moreover, it has been found that the shear flow strengths can be ranked using a parameter, W, derived from the matrix cracking stress in the absence of interface sliding,58 given by (Fig. 1.37),... 

As the stress is raised above the first matrix cracking stress, further cracking occurs resulting in a periodic crack array. Cao et al.55 have shown that the magnitude of the saturation crack spacing, d, is governed by the sliding stress, t, such that r and d are related by... 

It is obvious that the tensile strength and the first matrix cracking stress of these composites decreases significantly as temperature increases. 

Residual stress resulting from the thermal expansion mismatch between the fiber and matrix is another factor which will affect the interfacial properties, matrix cracking stress and the mechanical properties of ceramic... 

Non-oxide fibers cause composites to be susceptible to oxidative degradation, particularly when the matrix is cracked. Thus, the limiting stress at the present time is the matrix cracking stress (on the order of 100 MPa [14.5 ksi]). 

The room temperature tensile stress strain behaviors of 1 -D and 2-D SiC/Si3N4 monofilament composites showed high matrix cracking stress, but strain capability beyond matrix fracture is limited. Limited fiber pull out was observed on the tensile fracture surfaces [31]. 

D.B. Marshall and B.N. Cox, AJ-integral methodof calculation of steady-state matrix cracking stresses in composites , Mech. Mater. 7,1988,127-133. 

The better preservation of the strength reflects the fact that the composite cannot become weaker than the matrix cracking stress. At this point, as the strength is reduced to its lower limit, the properties of the composite are not much different from those of the matrix, which is characterized by a very low toughness, but with a... 

Similar trends of the effect of microfibre at 0.5% vol. reinforcement were reported by Yao era/. [125] for carbon microfibre, showing a pseudo-plastic behaviour for system with 0.2% carbon microfibre (7 /nm diameter, 5 mm long) and 0.3% vol. steel (0.5 mm diameter, 30 mm long), with a relatively smooth transition in the load-deflection curve around the matrix cracking stress. Qian and Stroeven [126] demonstrated the enhanced efficiency of hybrid reinforcement of 0.4 w/c ratio concretes, showing that a system of steel macrofibre and polypropylene microfibre could be used to obtain a flexural reinforcing effect at a fibre content of 0.75% vol., similar to that obtained with a higher content (0.9% vol.) of mono-steel macrofibres. 

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