patch size optimization

8/13/2019 Patch Size Optimization

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Adhesively

bonded composite patch have been shown to provide high

levels of bond durability under the operating conditions. It also offers

an efficient method for enhancing the structural integrity

which includes stiffening of under-designed regions, increasing

static strength, restoring strength or stiffness and reducing stressintensity factor (SIF).

Further, composite laminates have high

directional stiffness, high failure strain, durability under cyclic

loading, low density and excellent formability. Therefore, it is preferred

over isotropic patches which are predominantly made of

metal.

. the application

of bonded composite repairs to cracked primary structures isgenerally acceptable only on the basis of continuous monitoring

of patch performance to ensure that the load transfer is maintained

and also able to monitor damage growth in the parent/patch material. In case of

composite patch damages like delamination, matrix

cracking, and fiber pull out. should be detected and prevent further

catastrophic failures. Therefore, a suitable non-destructive testing

system should be devised for continuous online monitoring. From the

mechanical standpoint, two major challenges exist;

firstly, proper adhesion/bonding of the patch on the defective panel surface and

secondly selection of appropriate adhesive. For better

adhesion a good surface preparation is required and various techniquessuch as etching, shot peening or sand blasting. the choice of adhesive and itsthickness plays a major role on the integrity aspect and supposedly

it is the weakest link. Adhesives are generally classified as brittle, intermediate and ductile [15]. Depending upon the

combination

of parent and patch material one can choose the kind of adhesive. Lastly, the adhesive thickness influences the strength of thejoint as

the load is transferred from the base metal to the patch via the

adhesive. Thin adhesive layers are better than the thick layers becauseit gets the patch to be softer. But thickness provides good

durability to the entire patch as thick adhesive layer attracts lesser

strains. Good adhesive bonds are produced only in the range ofthickness 0.1250.25 mm

Patch repair is the most effective passive repair tecnique


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Patch repair may be done on one side of a damaged panel, or where possible,

symmetrically on both sides. The latter evidently produces a greater reduction in

stress intensity factor (SIF). This is

Sizes: economy of material

Service life extension: economic gain

Advancements will help move confidence of patches fromrepair of secondary to

primary repeair structures


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Perhaps A very large patch could be used instead of specialised shapes, but

economy of material is abandoned

patch size optimization

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