Failure Analysis Essay

3- Failure Analysis
Next, we perform a failure analysis in which the various structural response parameter just obtained are compared with their allowable or required values as following
Are the structural response parameters within design bounds?
Deflection too high?
Buckling loads too close?
Vibration frequencies near resonance?
Stresses too high? Less than strength?
Full-field stresses
Stresses around cutouts
Stresses around defects
The factors of safety for various types of failure can be very different from one another depending on weather we are designing against a catastrophic failure event or against a benign failure event.
Finally, failure analysis is the process of comparing actual performance with the desired performance. Thus, failure analysis is a nontrivial part of the structural design process.
4- Structural Reconfiguration.
Reconfiguration of a structure simply means to change some or all of the design variables such as thickness, fiber directions, stiffener sizes, etc. to achieve a more suitable structure than the current configuration. With the newly reconfigured structure, we go back to the analysis and failure analysis block in figure 00 evaluate the new configuration.
5- Design Objectives and Design Drivers.
A design objective is a statement of what we want the structure to do and /or to be. The three principle design objective are expressed in terms of functions, cost, and weight. Function is the set of the performance requirements or design requirements that the structure must meet or be able to do. Cost is the life-cycle cost of the structure. Weight is obviously the structure weight and might or might not be important. Note that function has many objective, whereas cost and weight are each single objective. It is not surprising that we use High-Stiffness-Low-Wight material such as composite materials to achieve the design objective of least weight.
a) Preliminary Design-Analysis
At the preliminary design-analysis stage of a structure, we make an initial attempt, i.e., take some kind of a first cut or approximation, at achieving a structural configuration to help define the weight. We also take first cut at satisfying the various system requirements which relate to function, as suggested below
First cut at structural configuration (weight).
Identify Design Drivers.
Perhaps use one-dimensional analysis.
First cut at system requirements (function).
First cut at manufacturing (cost).
Use a advanced computer program (Ansys).
b) Intermediate Design-Analysis
The Intermediate Design-Analysis stage is sometimes called trade studies.
More sophisticated analysis of competing design concepts.
Exercise design drivers.
Perhaps use two-dimensional analysis.
Assess impact of all concepts on weight, cost, and function.
Use computer program Ansys.
Fabricated and test simple models of critical components.
c) Final Design analysis.
Study final details of joints, cutouts, stiffeners, and system interactions in a sophisticated model.
Refine design drivers.
Perhaps use three-dimensional analysis.
Use a super-sophisticated computer program such as ansys.
Assess impact of all detail on weight, cost, and function.
Fabricate and test good simulation of critical components.