The ductile to brittle transition temperature is the temperature at which a material changes from ductile to brittle fracture. This temperature may be defined by the average energy between the ductile and brittle regions, at some specific absorbed energy, or by some characteristic fracture appearance. A material subjected to an impact blow during service should ha\e a transition temperature below the temperature of the material's surroundings.
Not all materials have a distinct transition temperature (Figure 6-20). BCC metals have ductile to brittle transition temperatures, but most FCC metals do not. FCC metals have high absorbed energies, with the energy decreasing gradually and, sometimes even increasing as the temperature decreases. As mentioned before, this transition may have contributed to the failure of the Titanic.
The ductile to brittle transition temperature is closely related to the glass temperature in polymers and for practical purposes is treated as the same. As mentioned before, the lower transition temperature or the polymers used in booster rocket O-rings and other factors led to the Challenger disaster.
(Essentials of Materials Science and Engineering, Donald R. Askeland,Pradeep P. Fulay,D. K. Bhattacharya, p.178)
Ductile to Brittle Transition Temperature (DBTT) : (Previous) (Better)
The
temperature below which a material behaves in a brittle manner in an
impact test. The ductile to brittle switchover also depends on the
strain rate. (pg214)
A
curve showing the trends iin the results of a series of impact tests
performed on nylon at various temperatures is shown in Figure 6-21. In
practice, the tests will be conducted at a
limited number of temperatures.
The
ductile to brittle transition temperature is the temperature at which a
material changes from ductile to brittle fracture. This temperature may
be defined by the average energy between the ductile and brittle
regions, at some specific absorbed energy, or by some characteristic
fracture appearance. A material subjected to an impact blow during
service should have a transition temperature below the temperature of
the material’s surroundings.
Not
all materials have a distinct transition temperature (figure 6-22). BCC
metals have transition temperatures, but most FCC metals do not. FCC
metals have high absorbed energies, with the energy decreasing gradually
and, sometimes, even increasing as the temperature decreases. The effect of this transition may have contributed to the failure of the Titanic.
In
polymeric materials, the ductile to brittle transition temperature is
related closely to the glass temperature and for practical purposes is
treated as the same. The lower transition temperature of the polymers
used in booster rocket O-rings and other factors led to the Challenger
disaster. (pg. 211,212)
(Askeland, D.R., Phule, P.P, The Science and Engineering of Materials, 5th Edition, pg. 211,212-214)
Plasma arc welding : (New) (Better) (Welding)
Plasma arc welding was developed in the 1960s for use in specialty and precision welding applications. The process works by creating an ionized gas called plasma. Many common materials, such as water and most gases, have three states: solid, liquid, or gas. The state the material is in depends on how much heat is applied to the material. For example, water is in a solid state (ice) when the temperature is below 32°F at atmospheric pressure. When heat is applied and the temperature rises above the freezing point it turns to a liquid. If more heat is applied, it turns to a gas (steam) when the temperature rises above 212°F. If enough heat is applied, the steam will become super heated and convert to a gas that will conduct electricity. This gas is called plasma and may be thought of as a sort of fourth state.
In the case of plasma arc welding, an inert gas called argon is heated until it converts into plasma, becomes ionized, and conducts electricity. In this process, a tungsten electrode begins an electric arc when electric current is passed through it. The plasma gas created by heating the argon is forced through a small opening that surrounds the tungsten electrode tip. The plasma conducts electricity that in turn produces a very intense heat in a small, very concentrated area. Unshielded arc welding creates a temperature of about 11,000F, but a plasma arc creates a temperature of about 43,000 F. The metal to be welded is melted and fused together very quickly. A secondary shield of argon or helium gas protects the molten puddle of metal.
The advantage of plasma arc welding is that it provides a very stable arc using a small amp current. This allows the welding of fine wire, and instruments smaller than a needle. Also, there is very little metal distortion with the plasma arc welding process.
(Agricultural Mechanics: Fundamentals and Applications, Ray V. Herren, p.426)
Plasma Arc Welding : (Previous)
It is an electric arc welding process which employs a high temperature constricted arc or plasma jet to obtain the melting and joining metal. In fact, the term “plasma” refers to a gas which is sufficiently ionized to conduct current freely. A conventional welding arc is an example of a plasma. A plasma jet is created when the arc is passed through a constricted nozzle. Due to this constriction, the plasma jet takes a narrow, columnar shape having properties ideal for welding.
(Adithan M., Gupta A.B., Manufacturing Technology, p.37)
Plasma arc welding : (New) (Better) (Welding)
Plasma arc welding was developed in the 1960s for use in specialty and precision welding applications. The process works by creating an ionized gas called plasma. Many common materials, such as water and most gases, have three states: solid, liquid, or gas. The state the material is in depends on how much heat is applied to the material. For example, water is in a solid state (ice) when the temperature is below 32°F at atmospheric pressure. When heat is applied and the temperature rises above the freezing point it turns to a liquid. If more heat is applied, it turns to a gas (steam) when the temperature rises above 212°F. If enough heat is applied, the steam will become super heated and convert to a gas that will conduct electricity. This gas is called plasma and may be thought of as a sort of fourth state.
In the case of plasma arc welding, an inert gas called argon is heated until it converts into plasma, becomes ionized, and conducts electricity. In this process, a tungsten electrode begins an electric arc when electric current is passed through it. The plasma gas created by heating the argon is forced through a small opening that surrounds the tungsten electrode tip. The plasma conducts electricity that in turn produces a very intense heat in a small, very concentrated area. Unshielded arc welding creates a temperature of about 11,000F, but a plasma arc creates a temperature of about 43,000 F. The metal to be welded is melted and fused together very quickly. A secondary shield of argon or helium gas protects the molten puddle of metal.
The advantage of plasma arc welding is that it provides a very stable arc using a small amp current. This allows the welding of fine wire, and instruments smaller than a needle. Also, there is very little metal distortion with the plasma arc welding process.
(Agricultural Mechanics: Fundamentals and Applications, Ray V. Herren, p.426)
Plasma Arc Welding : (Previous)
It is an electric arc welding process which employs a high temperature constricted arc or plasma jet to obtain the melting and joining metal. In fact, the term “plasma” refers to a gas which is sufficiently ionized to conduct current freely. A conventional welding arc is an example of a plasma. A plasma jet is created when the arc is passed through a constricted nozzle. Due to this constriction, the plasma jet takes a narrow, columnar shape having properties ideal for welding.
(Adithan M., Gupta A.B., Manufacturing Technology, p.37)
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