# energy balance of surface-based cohesive of composite under impact in Absqus 6-10

Hi there! I am really new to Abaqus and I need to model a composite
laminated crash cone under impact to a flat solid wall (analytical
surface is used). I modelled a cone with a layers of conventional shell
elements with hashin failure criteria and surface-based cohesive
behaviour as interaction between layers representing the interface of
composite laminates. The model runs successfully but once I checked the
energy balance, the damage dissipation energy from the cohesive, it
turned out to be NEGATIVE (I think this is wrong).
I tried to model a simple geometry model with cohesive elements and the
damage energy from cohesive element is POSITIVE (which seems to be
correct).

As far as I know the energy balance: internal energy =
strain energy + artificial energy + damage dissipation energy + penalty
contact energy +contraint penalty energy + plastic energy

where Total energy = internal energy + viscous energy + kinetic energy + frictional energy + external work = constant
I set up another history field output request to capture the energy of
hashin damage to compare with the all damage energy of model and the
result is that damage from surface-based cohesive is NEGATIVE. This
means the more damage to the cohesive, the less internal energy in the
cone which means that less energy absorbed from the impact. <--
totally wrong...

Due to the complex geometry of the model, cohesive element does not seem to the one I can apply to my model.
Could anyone explain or give me a solution why the damage energy from surface-based cohesive is NEGATIVE? Is it wrong?

Here is the interaction property of the surface-based cohesive

** INTERACTION PROPERTIES
**
*Surface Interaction, name="interface prop"
*Cohesive Behavior, eligibility=ORIGINAL CONTACTS
20000.,15000.,15000.
*Damage Initiation, criterion=QUADS
60.,90.,90.
*Damage Evolution, type=ENERGY, softening=EXPONENTIAL, mixed mode behavior=POWER LAW, power=2.
0.6,2.,2.
*Contact Damping, definition=CRITICAL DAMPING FRACTION
0.1,