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Factors of Design and Safety

Factors in Design

Complexity of stress analysis

Consequences of failure

Environmental exposure

Material Strength

Potential Misuse of the Product

Factors in Design (continued)

Quality Control

Size or Mass Effect

Stress Concentration Factors

Types of Loads

Type of Material

Cost

Factor of Safety

• Used by engineers to account for uncertainty in applied forces, material properties, model assumptions, etc.

• The allowable stress in the part is determined by the following formula.

• An acceptable design is when the calculated stresses in the part are less than the allowable stress.

Allowable Stress = Material Strength Factor of Safety

Factor of Safety

Multiplier for Factor of Safety

  Ductile Materials Brittle Materials

Type of load Yield Strength

Ultimate Strength

Ultimate Strength

Static 2 - 6

Repeated - 8 10

Impact - 12 15