The experimental determination of the resistance to delamination is very important in aerospace applications as composite materials have superior properties only in the fiber direction. To measure the interlaminar fracture toughness of composite materials, different kinds of specimens and experimental methods are available. This article examines the fracture energy of four-point end-notched flexure (4ENF) composite specimens made of carbon/epoxy and glass/epoxy. Experiments were conducted on these laminates and the mode II fracture energy, II , was evaluated using compliance method and was compared with beam theory solution. The crack growth resistance curve (R-curve) for these specimens was generated and the found glass/epoxy shows higher toughness values than carbon/epoxy composite. From this study, it was observed that R-curve effect in 4ENF specimens is quite mild, which means that the measured delamination toughness, II , is more accurate.
It can be M1tit to effeet a timely fracturing fluid bx tier a hydradic ticturing titment in resetvok above 190"F. Fracturing fluid systems often are quite stable at ternperatis up to 300"F. At eIevated tempemw the~tment designer is faced with the selection of~cturing fluid breaker @m three main categories: otidizers, acids and enzymes.Typical oxidizing breakers systems, used at temperatures up to 250°F,~@ates ofien encaptiated by a thin fflm of polymer. Encapmkted p-ates ofien "leak" allowing some of the encapsulated b@er to be rapidly released into the fracturing fluid'. EarIy release of oxidizing breaker degrades the ticturing fluid during the fracturing treatment--before the desired time.Acids can be used as breakers but m usually limited to lower temperaws. In additio~the buffering capacity of the formation and the fmcturing fluid can significantly impact the performance of acids and finrdly, acids w usually less cost effective than other b-m.Polymer speeific enzymes, while an eff~ve breaker at elevated t~~do not provide a rapid break in fluids with a high PH.The industry Ms developed an appreciation of minhuizing gel loadings in ficturing fluids because of perceived high insitu polymer concentrations brought about during fracture closure.%3'4.For this reasomit is desimble to use breaker systems that do not prematurely attack fluid viscosity, atlowing use of the *um gel loading that adequately transports proppant.A high tempemture, ticturing fluid br+er system that ciwmvents many of the problems discussed has been developed. The breaker systq instead of relying on a microthin mting on a vw mctive substrate, provides a cliff-t app-h to the problem. The alternative breaker system discussed here utilizes a non-encapfited, otidizing b-er that effwts a delayed break by slowly releasing free radicals in water based fracturing fluids, thus degrading Mcturing fluids in a controlled manner,
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