Engineer Design - Module 2

Assemblies

What is a Component

Object that makes up an assembly

What is an Abutment

identical objects brought into an assemblies just oriented differently

What are Instances

Copies of a component within an assembly

What is a Subassembly

a grouping of components that serve a single purpose

Why are subassemblies useful

linking them in a subassembly allows for later modification, if needed, rather than making it a whole part.

What is Associativity

If you change the geometry of a part the components and all instances will change by the same amount

What’s a good example of Associativity

If a company wants to modify a part of a foot bridge, they use across a rec center, then associativity will change the rest of the bridges

What is assembly hierarchy

Is subassembly to subassembly to subassembly until the subassembly is fully defined.

What us a Parent-Child relationship

association b/w components and subassemblies

Example of a Parent-Child relationship

Parent: Handrail is the parent

Child: The horizontal, vertical components, and the angled assembly are children.

What is a Base instance

is a component that remains stationary while other instances are being placed

Why are assembly constraints useful

So instances can maintain dimensional or geometric relationship with respect to each other within an assembly

Once you bring a instance into an assembly what is one thing to note?

The instance will have 6 Degrees of freedom (DOF)

Concentric constraints

Useful when dealing with cylindrical shafts within a cylindrical hole

what is Mating surfaces

Used to defined two surfaces

Mating surfaces coincides with each other, in other words line up[ on top of each other.

you are forcing the normal of two objects to be parallel

What is an Offset

The surfaces normal are still parallel, but the surfaces are now not on top of each other

Coincident constraints

Two entities that take up one space

Typically you select the corner or edge of two object to coincide with one another

Distance Constraints

Define a distance relationship b/w two instances

what are some inertial properties

• Radii-of-gyration

• moments-of-inertia

• principle-axes of rotation

• Products of inertia

Measure analysis

can determine dimensions and other geometric parameter of the CAD

What are some Measure analysis?

• Measure point- Used to find coordinates of a point

• Measure line length - Used to measure the length of a line

• Measure line distance- Measure the shortest distance of a line to another identified entity

• Measure circle- Measure diameter

• Measure arc

• Measure surface - Measure area and perimeter of the surface

Mass properties

• Static Properties of a solid body

• Depends on two things: Geometry and its density

• Mass properties are related to one another through various formulas

• Offers fast insight into the appearances of a design concept

Examples of Mass properties

Density- Mass/volume

Radius of gyration- object inertia about that same axes

moments-of-inertia - The weight of the mass multiplied by a distance the mass is away from the rotational axis

Interference

the amount that two instances overlap

Clearences

the distances b/w parts

Common places to check for instances and clearance

shafts and circular holes

Finite Element Analysis (FEA)

advance design technique obtained by 3-D CAD tools

Is in the category of engineers analysis tools that apply computational approximation to classic field problems

Example of FEA: stress

can be calculated by the pulling force divided by the cross-sectional area of the rod

What happens if stress is to large

can result into permanent changes in the object

What a way to reduce stress

increase the cross-sectional area

FEA’s method

Dividing the part into individual pieces called a mesh

What is a single part of a mesh

They are called elements

Types of FEA methods

Mechanical stress and displacement fields - object that experience loads

Shear stress - tries to slides molecules apart in motion and possibly shear them/disoriented

FEA methods : Fluid flow and pressure fields

Allows engineers to compute the airflow around airplane wings

FEA methods: Thermal flows and temperature fields

Computation of thermal flow and temp.

FEA methods: Electromagnetic fields

When electricity flows through a wire a electromagnetic field is created

How are the finite elements connect

The finite elements are connect through their edges and nodal points that specify the boundary conditions

FEA Process

• Create the model geometry

• apply constraints (FEA requires a fully defined constraint)

• applying loads

• Meshing.

For stress analysis What are the two interest quantities

Stresses and displacement

What is Von Mises

used to predict yielding of materials under complex loading

Red contours: signify high stress

Blue contours: signify low stress