Exempel tentafrågor Flashcards
What do we mean by translation?
The translation shall translate the demands on the component to demands on the material that we can use in the material selection.
What part does a translation consist of?
It consists of four parts:
- Function: defining the main function of the material in the component, including load case for
mechanical loads
- Constraints: Material properties that must be fulfilled for the components to function
- Objective: The property of the component that we want to optimise
- Free variables: Things we are free to change
What do we mean by translation?
The translation shall translate the demands on the component to demands on the material that
we can use in the material selection.
We are usually using the fracture toughness when we are dimensioning against fracture or choosing a material to withstand fracture. Explain fracture toughness and when we get fracture.
Fracture toughness is a material property that describes what load is needed for a crack to propagate(spridas/ske?).
The crack will propagate when the stress intensity factor (depending on load and crack length) is larger than the fracture toughness.
We are often using performance indexes when we are doing a material selection. Explain what a performance index is used for. What do we need to know to determine a performance index?
Used for: Performance index is a numerical value that tells how well different materials are fulfilling the objective. It is used to rank the materials.
To determine the material index: we are using function, objective and free variables.
There are two main types of fracture. Name, describe and explain the two types.
Brittle fracture. Brittle fracture is a type of fracture with little energy involved in the crack propagation. This type of fracture is common for ceramics and glasses.
Ductile fracture: A type of fracture with large amount of energy involved in the crack propagation, due to plastic deformation at the crack tip. Common for plastics and metals.
Ceramic materials are one of the three main groups of materials. How do we define a ceramic material, and what are the main characteristics of ceramic materials?
Ceramic materials are a compound of at least one metal and one non-metal.
The main characteristics are: high melting temperature, high stiffness, no plastic deformation, brittle, good thermal and electric isolator.
The properties of ceramic materials are important for the possible ways can form ceramic components.
What properties are determining for the forming processes? Describe how ceramic components (usually) are manufactured.
The high melting temperature makes it difficult to cast ceramic materials.The brittleness make it impossible to form ceramics with plastic methods.
To form ceramic materials we are usually starting with clay or powder that is formed to the desired shape. The material is then sintered = heated to 2/3 of the melting temperature so that the material is bonded together with the help of diffusion.
What environmental considerations can we do when choosing material?
How great is the environmental impact in manufacturing and how good is the material when recycling. What forming and manufacturing methods should we use
What different types of fatigue exist? (2)
1.Low cycle fatigue: characterised by high loads, global plastic deformations, and less than 10.000 cycles to failure.
2.High cycle fatigue: load under the yield stress, no global plasticity, more than 10.000 cycles to failure.
Fatigue is one of the common reasons to failure of metal components. What do we mean by metal fatigue? Describe and explain the mechanisms of fatigue.
Fatigue is a phenomenon that can occur when a metal is loaded with a varying load. First, a small crack is initiated at some defect or stress concentration. The crack then propagates due to local plastic deformation at the crack tip, giving a small crack advance for each load cycle. When the crack is so long that the fracture toughness is reached, we get a final fracture
The most common choice of material when we are making components of metals are ____ and _____, as they have good price and good general properties.
steel, aluminium
Special properties and application of: Mg
Properties: Low density, relatively low mechanical properties, relatively brittle, low melting temperature, difficult to form plasticity, good casting properties.
Applications: Castings with complicated shape, moderately loaded lightweight components
Special properties and application of: Ti
Properties: High yield stress, lower density than steel but higher than aluminium and magnesium, operating temperature up to 500 °C, excellent corrosion properties, bio compatible, high price, and high CO2 footprint.
Applications: medical implants, high strength low weight components up to 500 °C.
Special properties and application of: Ni base super alloys
Properties: Excellent strength at high temperature, excellent corrosion, and oxidation resistance.
Applications: gas- and jet turbines, chemical process equipment
