20-06-2011, 10:04 AM
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• Mechanical components can fail at stresses well below the tensile strength of the material if subjected to alternating loads.
• Failure of ductile materials under alternating loads occurs in a quasi brittle manner, i.e. by crack propagation.
• Failure is preceded by characteristic changes in the material microstructure
• This phenomenon is called ‘Metals Fatigue’.
This Figure below shows a laboratory fatigue specimen. They are machined with shape characteristics which maximize the fatigue life of a metal, and are highly polished to provide the surface characteristics which enable the best fatigue life.
A single test consists of applying a known, constant Bending Stress to a round sample of the material, and rotating the sample around the bending stress axis until it fails. The test mechanism counts the number of rotations (cycles) until the specimen fails. The cyclic stress level that the material can sustain for 10 million cycles is called the Endurance Limit (EL).
1. Drop Forging:
2. Powder Forging: Powder forging is a process in which powders such as iron and copper are compacted, heated and forged so that their density increases up to that of wrought steel.
3. Die casting: Die-casting is accomplished by forcing molten metal under high pressure into reusable metal dies.
1. Monotonic Tension Test:
All monotonic tests in this study were performed using test methods specified by ASTM Standard E8.
One specimen was used from each material to obtain the monotonic properties.
Raw material is cheaper than powder metal.
This process provides high strength, ductility, and impact resistance along the grain flow of the forged steel.
The density achieve by this process is uniform.
Fatigue performance of forged steel rods is higher than die cast and powder metal rods.
In conventional forging, flash is produced during forging and requires extra steps of trimming to remove.
To ensure proper weight balance, conventional connecting rods are provided with excess weight, which is later remove during finishing operations.
The rough stock weigh required is more than needed for connecting rod, resulting in some scrap.
Powder metal preform connecting rods start with the net shape, that result in no material waste.
There is no balancing pad used in this Process.
Fracture splitting of cap from rod without subsequent machining of matching surfaces is most popular for powder metal connecting rods.
Raw material of this process is expensive because of operations of powder formation, presintering, and sintering.
Lower mechanical properties because of rapid solidification.
During compacting trapped oxygen in the powder results in porosity, decarb, and oxide penetration.
The density can vary within powder metal connecting rod.
Costly part density modification or infiltration is required to prevent powder metal defect.
From tensile tests and monotonic curves it is concluded that forged steel is considerably stronger than the powder metal.
Yield strength of forged steel is 19% higher than that for the powder metal. Ultimate tensile strength of forged steel is 8% higher than that for the powder metal.
Better fatigue resistance of the forged steel material, as compared with the powder metal material was observed.
Based on strain-life fatigue behavior, the forged steel provides about a factor of 7.
longer life than the powder metal in the high cycle regime.
Fatigue limit (Nf = 106 ) for powder metal is 79% of that for the forged steel.
• Mechanical components can fail at stresses well below the tensile strength of the material if subjected to alternating loads.
• Failure of ductile materials under alternating loads occurs in a quasi brittle manner, i.e. by crack propagation.
• Failure is preceded by characteristic changes in the material microstructure
• This phenomenon is called ‘Metals Fatigue’.
This Figure below shows a laboratory fatigue specimen. They are machined with shape characteristics which maximize the fatigue life of a metal, and are highly polished to provide the surface characteristics which enable the best fatigue life.
A single test consists of applying a known, constant Bending Stress to a round sample of the material, and rotating the sample around the bending stress axis until it fails. The test mechanism counts the number of rotations (cycles) until the specimen fails. The cyclic stress level that the material can sustain for 10 million cycles is called the Endurance Limit (EL).
1. Drop Forging:
2. Powder Forging: Powder forging is a process in which powders such as iron and copper are compacted, heated and forged so that their density increases up to that of wrought steel.
3. Die casting: Die-casting is accomplished by forcing molten metal under high pressure into reusable metal dies.
1. Monotonic Tension Test:
All monotonic tests in this study were performed using test methods specified by ASTM Standard E8.
One specimen was used from each material to obtain the monotonic properties.
Raw material is cheaper than powder metal.
This process provides high strength, ductility, and impact resistance along the grain flow of the forged steel.
The density achieve by this process is uniform.
Fatigue performance of forged steel rods is higher than die cast and powder metal rods.
In conventional forging, flash is produced during forging and requires extra steps of trimming to remove.
To ensure proper weight balance, conventional connecting rods are provided with excess weight, which is later remove during finishing operations.
The rough stock weigh required is more than needed for connecting rod, resulting in some scrap.
Powder metal preform connecting rods start with the net shape, that result in no material waste.
There is no balancing pad used in this Process.
Fracture splitting of cap from rod without subsequent machining of matching surfaces is most popular for powder metal connecting rods.
Raw material of this process is expensive because of operations of powder formation, presintering, and sintering.
Lower mechanical properties because of rapid solidification.
During compacting trapped oxygen in the powder results in porosity, decarb, and oxide penetration.
The density can vary within powder metal connecting rod.
Costly part density modification or infiltration is required to prevent powder metal defect.
From tensile tests and monotonic curves it is concluded that forged steel is considerably stronger than the powder metal.
Yield strength of forged steel is 19% higher than that for the powder metal. Ultimate tensile strength of forged steel is 8% higher than that for the powder metal.
Better fatigue resistance of the forged steel material, as compared with the powder metal material was observed.
Based on strain-life fatigue behavior, the forged steel provides about a factor of 7.
longer life than the powder metal in the high cycle regime.
Fatigue limit (Nf = 106 ) for powder metal is 79% of that for the forged steel.
