Pull out work

Figure 4.5 Effect of length (a) and bond (b) on the contribution (efficiency) of the fibre to strength, Pf, and toughness (pull out work, Wp), Pf, is proportional to the fibre efficiency fector, rj.

Figure 8.28 Pull-out work vs. bond strength calculated for GRC composite (after Bentur [I I]).

But it does not usually do this. We have already seen that, if the length of the fibres is less than 2x, they will not fracture. And if they do not fracture they must instead pull out as the crack opens (Fig. 25.6). This gives a major new contribution to the toughness. If the matrix shear strength is tr (as before), then the work done in pulling a fibre out of the fracture surface is given approximately by... 

Adhesiveness, defined as the work necessary to overcome the attractive forces between the surface of the sample and the surface of other materials with which the food comes into contact, e.g. tongue, teeth, palate, etc. (Szczesniak, 1963), is given on the texturometer curve by the negative force area, representing the work needed to pull out the plunger from the sample. This parameter s value may be considered an evaluation of stickiness of jelly. Fracturability, also called brittleness, is given by the measure (%) of the plunger path into the jelly when it breaks. 

Recently, Oldfield Ellis (1991) have examined the reinforcement of glass-ionomer cement with alumina (Safil) and carbon fibres. The introduction of only small amounts of carbon fibres (5% to 7-5% by volume) into cements based on MP4 and G-338 glasses was found to increase considerably both the elastic modulus and flexural strength. There was an increase in work of fracture attributable to fibre pull-out. A modulus as high as 12-5 GPa has been attained with the addition of 12% by voliune of fibre into MP4 glass (Bailey et al, 1991). Results using alumina fibre were less promising as there was no fibre pull-out because of the brittle nature of alumina fibres which fractured under load. 

I was still breathing. I knew I had to get supplemented with thyroid hormone, and I couldn t imagine what was going to work. I couldn t see how I was going to pull out of it. Death seemed imminent. 

By the time I was in the fifth grade my mom was educated and my doctor helped her to realize I couldn t go to school in that building. She pulled me out of school and got a tutor to work with me at home. That was a pretty hard time for me. I didn t want to be pulled out of school nobody does at that age. School is your only connection to a social life. So, I wasn t happy about it but I knew it was the right decision. The school wasn t a safe place for me, or for anyone, for that matter. When I stopped going to that school I started the process of getting healthy. 

In an approach similar to that adopted in the work of Greszczuk (1969) on the fiber pull-out test, Piggott (1980) has obtained solutions for the stress fields in the fiber for several different cases of fiber-matrix interface, including the perfectly... 

Mai (1985) has also given a review of the fracture mechanisms in cementitious fiber composites. The total fracture toughness, / i, is given by the sum of the work dissipation due to fiber pull-out, fiber and matrix fraetures, fiber-matrix interfacial debonding and stress redistribution, i.e.. 

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