3.4 Consider the panel loaded as shown below, which has a central crack 2 inches

Question

3.4 Consider the panel loaded as shown below, which has a central crack 2 inches in length oriented perpendicular to the applied load. The materials listed below are being considered for this application. crack 50 in 500,o00 lb Material Static strength, Fracture toughness, Density FTy (ksi) Kapp (ksi-in) p (lb/in) 7075-T651 7055-&7751 2024-T351 2324-T39 Ti-6-4 69 86 48 62 120 226 67 85 141 142 150 100 .101 102 .101 101 .160 283 -4340M What is the lightest adequate panel to survive the loud irs a. only static strength is considered? b. fracture toughness is considered? c. both criteria are considered?

Explanation / Answer

Stress concentration

occurs at transition of

cross sections. The more

abrupt the transition, the

higher are the stress

concentrations.

Stress Concentration Factor Kt

Kt is difficult to calculate and it is usually determined by some

experimental technique (photoelastic analysis of a plastic model or by

numerical simulation of the stress field).

The values of Kt can be found published in Charts.

The values of Kt are geometric properties.

Kt is very important in brittle materials.

In ductile materials, Kt is very important in fatigue calculations. I

must be taken into account if safety is critical.

Photoelasticity : Photoelasticity is a visual method

for viewing the full field stress distribution in a

photoelastic material. When a photoelastic material

is strained and viewed with a polariscope, distinctive

colored fringe patterns are seen. Interpretation of the

pattern reveals the overall strain distribution.

Radiometric Thermoelasticity : When materials are stressed the change

in atomic spacing creates temperature differences in the material.

Cameras which sense differences in temperature can be used to display

the stress field in special materials.

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