Unit Conversion

Length

Meters Millimeters Micrometers Feet Inch to Meters Millimeters Micrometers Feet Inch

Result:

Mass

Kilograms (kg) Grams (g) Metric Tonnes (tonne) Slugs (slug) (lbf·s²/in) to Kilograms (kg) Grams (g) Metric Tonnes (tonne) Slugs (slug) (lbf·s²/in)

Result:

Time

Seconds Minutes Hours Days to Seconds Minutes Hours Days

Result:

Force

Newtons (N) Kilonewtons (KN) Pounds (lb) Dynes (dyn) to Newtons (N) Kilonewtons (KN) Pounds (lb) Dynes (dyn)

Result:

Stress

Pascals (Pa) Megapascals (MPa) Kilopascals (kPa) Pounds per Square Inch (psi) to Pascals (Pa) Megapascals (MPa) Kilopascals (kPa) Pounds per Square Inch (psi)

Result:

Energy

Joules Kilojoules lbf.ft lbf.in Ergs To: Joules Kilojoules lbf.ft lbf.in Ergs

Result:

Density

kg/m³ ton/mm³ slug/ft³ lb/in³ To: kg/m³ ton/mm³ slug/ft³ lb/in³

Result:

---

Understanding Units in ABAQUS

When you start using ABAQUS, a powerful finite element analysis software, you'll probably have a common question: "What units are used in ABAQUS?" Unlike some other FE software, ABAQUS doesn't impose any particular unit system. The responsibility for ensuring consistent units lies with the user and selecting a consistent unit system is crucial before performing FE simulations. There are numerous different sets of units that can be used in FE simulations. Here is a table of typical unit sets:

Quantity	SI	SI (mm)	US Unit (ft)	US Unit (inch)
Length	m	mm	ft	in
Force	N	N	lbf	lbf
Mass	kg	tonne (10³kg)	slug	lbf s²/in
Time	s	s	s	s
Stress	Pa (N/m²)	MPa (N/mm²)	lbf/ft²	Psi (lbf/in²)
Energy	J	mJ (10⁻³J)	ft lbf	in lbf
Density	kg/m³	tonne/mm³	slug/ft³	lbf s²/in⁴

So, how do you go about choosing the suitable unit systems for FE analysis?

A fundamental guideline when selecting unit systems for FE analysis is to aim for values close to unity. When input quantities are close to 1 in their respective units, several advantages come into play. Most notably, rounding errors and truncation errors are dramatically reduced, ensuring the precision of your simulation results. To illustrate this concept, consider a scenario where you opt for millimeters (mm) as your unit for length, Newtons (N) for force, and then specify Young's modulus in kilonewtons per square meter (KN/m²). Such a mix of inconsistent unit choices can introduce confusion and errors into your analysis.

Now, let's explore an alternative scenario where you've designed your model using meters (m) as the unit for length (L). In this scenario, all derived quantities based on length will naturally be expressed in meters. To maintain consistency, you can opt for the International Unit System (SI) units for other physical properties. For instance, if you're working with steel, your material properties can be specified as follows:

- Young's Modulus: (E=210 * 10^9 Pa)

- Poisson's Ratio: (nu=0.3)

- Density: (rho=7800 kg/m³)

This approach of consistent units, with meters as the base for length, helps maintain clarity and accuracy throughout your analysis.However, this approach can result in working with large quantities, which may not be ideal for certain simulations.

To mitigate this issue, ABAQUS offers a coherent unit system that allows us to make a thoughtful choice of fundamental quantities for our model. The choice of unit systems in mechanics often depends on the size of the model. Here are some convenient unit systems, depending on model dimensions:

Micro-Level	Meso-Level	Macro-Level
The micro-level represents the smallest scale within the material. It often deals with the microsructure of materials, simulations may involve atomistic or molecular modelling techniques to understand the behavior of individual particles. In this system, the fundamental dimensions are: - Length in nanometers or micrometers (nm)/(μm) - Force in picoNewtons or milliNewtons (pN)/(mN) - Time in seconds (s) - Stress in picopascals or gigapascals (pPa)/(GPa) In this Micromechanics unit system, the choice of microns and gigapascals allows for precise analysis of microscopic phenomena, making it ideal for extremely small scale models.	The meso-level represents the intermediate-scale models, bridging the gap between the micro and macro scales. In this system, the fundamental dimensions are: - Length in millimeters (mm) - Force in newtons or kiloNewtons (N)/(kN) - Time in seconds (s) - Stress in megapascals or gigapascals (MPa)/(GPa) The Mesomechanics unit system is commonly used to analyze materials with larger structural components or mesostructural features, such as the analysis of composite materials, concrete structures, and biomechanics studies.	The macro-level represents the largest scale model and is relevant for practical engineering applications, such as bridges, dams, or power plants that span hundreds of meters. In this system, the fundamental dimensions are: - Length in meters (m) - Force in meganewtons (MN) - Time in seconds (s) - Stress in megapascals (MPa) The Macromechanics unit system is essential for the simulation and analysis of real-world engineering problems. It provides units that are practical for describing and quantifying the behavior of large structures and materials, making it directly applicable to industries to industries such as civil engineering, aerospace, and mechanical engineering.

In conclusion, choosing the appropiate unit system is essential for accurate FE analysis. By selecting units that align with the dimensions and scale of your model, you can enhance the precision of your simulations and obtain reliable results. Remember, it's all about aiming for values close to unity to minimize errors and achieve robust outcomes in your FE analysis.

Written by: Theingi Nwe