Contact Resistance
The thin interface between two layers decides how heat flows through a composite lay-up, and with it the bonding, crystallinity and residual stress of the final part.
Thank you for reading this post, don't forget to subscribe!Every new layer is placed hot onto a cooler substrate. How much of that heat crosses the interface, and how fast, is governed by thermal contact resistance. It is one of the main reasons that two lay-ups with the same laser power can end up with different quality.
In short
What contact resistance does
- Creates a temperature jump at the interface between layers
- Controls how quickly heat leaves the nip point into the substrate
- Shapes the temperature evolution through the thickness and over time
- Changes as the layers consolidate, so it is not a fixed number
Two thermal scenarios
Low resistance
Intimate contact
- Heat passes easily into the layers below
- A smooth temperature profile through the thickness
- The interface reaches bonding temperature more uniformly
- More laser power may be needed, because heat drains away faster
High resistance
Poor contact
- A sharp temperature drop across the interface
- Heat stays in the top layer, which risks overheating at the surface
- The interface may stay below melt, giving weak bonding
- Steeper gradients raise residual stress and warpage
What drives contact resistance
Surface condition
- Tape surface roughness
- Resin-rich or resin-poor surfaces
- Gaps, overlaps and waviness
Consolidation
- Roller force and roller deformation
- Degree of intimate contact over time
- Placement speed and dwell under the roller
Temperature
- Matrix viscosity above melt
- Substrate temperature from earlier courses
- Cooling between successive layers
How OTOM accounts for it
- Interface model: a thermal contact conductance between the placed tape and the substrate, so the temperature jump appears where it physically occurs.
- Layer-on-layer simulation: the substrate model carries accumulated heat from earlier plies (cumulative substrate heating), so contact acts on the real thermal history.
- Calibration: contact parameters are tuned against thermal-camera measurements for your tape and machine.
- Downstream effects: the resulting temperature history feeds crystallisation kinetics and the residual-stress model.
- Optimisation: laser power is adjusted per station to keep the interface in the bonding window, whatever the contact condition.
Design takeaways
For process engineers
- Balance heat input against consolidation force, not either alone
- Watch the first plies and the interface temperature, not only the surface
- Expect a different optimum on a warm substrate than on a cold one
For product designers
- Thick lay-ups accumulate heat, so plan the cooling time between plies
- Uniform consolidation gives uniform properties
- Interface quality limits interlaminar strength
Unsure how contact affects your set-up?
Our team can model your tape, roller and process and show you where the interface temperature really is.