- The stress that will cause a specified small, permanent extension of a tensile test piece. Commonly the stress to produce 0.2% extension is quoted in N/mm2 for steel. This value approximates to the yield stress in materials not exhibiting a definite yield point.
- The load per unit area that a structure can withstand without being permanently deformed by more than a specified amount. Stress that will cause a specified permanent deformation.
- Proof stress can be found by referring to the stress/strain curve at the point where strain is = 0.2% original volume (the material has grown 0.2% in volume) proof stress will be given as a measurement of energy (MPa,KPa etc.) as it specifically refers to the amount of energy required to stress the material to 0.2% its original volume.
- Proof stress, by definition, is the stress to cause some level of permanent deformation.
1. High cost: Manganese bronze is a costly alloy, making it less economical for large propellers. 2. Low strength-to-weight ratio: Compared to other propeller materials like nickel-aluminum bronze or stainless steel, manganese bronze has a lower strength-to-weight ratio. 3. Susceptible to corrosion: Manganese bronze can corrode in seawater, especially when exposed to high velocities and turbulence. 4. Poor cavitation resistance: Manganese bronze is more prone to cavitation damage than other materials. 5. Difficult to cast and machine: Manganese bronze is challenging to cast and machine, making it less desirable for complex propeller geometries. 6. Limited weldability: Manganese bronze has poor weldability, making repairs and modifications difficult. Nickel-aluminum bronze or stainless steel are commonly used for propellers due to their: - High strength and durability - Excellent corrosion resistance - Good cavitation resistance - Ease of casting and machining - Weldability
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