M11 — Contact · Learn to Program Ansys APDL Simulations

M10 introduced geometric and material nonlinearity. M11 opens the second optional specialization: structural contact between two 3D bodies. You will define a CONTA174/TARGE170 pair, run CNCHECK before solving, and document gap, penetration, and closing reaction with CSV evidence.

Your mission

You will build two stacked blocks, create the contact pair, audit the initial state, close the contact with controlled displacement, and compare three verifiable cases in CSV.

Guiding question: can you prove whether contact is open or closed before trusting the stresses?

Objectives

After completing M11, you will be able to:

Select surfaces and generate CONTA174 and TARGE170 elements with ESURF.
Configure a frictionless pair with consistent REAL, TYPE, and KEYOPT settings.
Run CNCHECK,AUTO and document the initial gap or penetration.
Solve with NLGEOM,ON, ramping (KBC,0, NSUBST), and rigid-body-motion constraints.
Extract support reactions and determine contact_closed using a numerical criterion.
Diagnose common faults by reading the .out file and audit CSV.

Prerequisites and downloads

M06: substeps and global equilibrium.
M10 (recommended): NLGEOM and nonlinear convergence.
M02: robust surface selection (ASEL, SELTOL).

11_start.mac — starting point.
11_contact_pair.mac — audited deliverable.
11_bug_hunt.mac — five faults.
11_challenge.mac — verifiable challenge.
11_expected_results.csv — numerical contract.
contact-pair-setup.svg — contact/target pair.
initial-gap-penetration.svg — initial states.

How to use this lesson

Path	Duration	Coverage
First win	20–25 min	Geometry, contact pair, `CNCHECK`, and first CSV.
Complete	70–75 min	Three cases, POST1, debugging, challenge, and mastery.

Session map

Mission: objectives, downloads, and prediction.
Mental model: contact versus target, normals, and gap.
Demonstration: geometry, pair, CNCHECK, and solution.
Debugging: five common faults.
Challenge: friction or gap variation.
Mastery: final M11 test.

Prediction — What happens before SOLVE?

Two 40 × 40 × 20 mm blocks with an initial 0.5 mm gap.

Quantity	Value	Interpretation
Initial gap	0.0005 m	Open pair in `CNCHECK`
Case 1 displacement	−0.0002 m	Does not close the gap → no load transfer
Case 2 displacement	−0.0012 m	Closes the gap and compresses → support reaction
Topology	150 nodes / 64 solids / 16+16 contact	Mesh consistent with `mesh_h = 0.01 m`

Prediction: with disp = −0.2 mm, contact remains open (contact_closed = 0). With disp = −1.2 mm, it must close and produce a vertical reaction at the lower support.

Mental model — Contact pair

3D blocks with CONTA174 and TARGE170 — Figure 1. Target surface on the lower block; contact on the upper block; normal pointing toward the gap.

Contact: CONTA174 — surface that may penetrate the target.
Target: TARGE170 — reference surface.
Initial state: CNCHECK reports gaps, penetration, and open/closed pairs.
Frictionless: KEYOPT,2,12,0 in the base deliverable.

Step 1 — Geometry and mesh

BLOCK,0,block_x,0,h_lower,0,block_z
BLOCK,0,block_x,h_lower+initial_gap,h_lower+initial_gap+h_upper,0,block_z
VMESH,ALL

Use SELTOL when selecting faces at Y = h_lower and Y = h_lower + initial_gap.

Two 3D blocks with a visible initial gap in a MAPDL side view — Figure 2. Side view: initial `0.5 mm` gap between the blocks before `ESURF`.

Step 2 — Define the CONTA/TARGE pair

ET,2,CONTA174
KEYOPT,2,12,0
ET,3,TARGE170
TYPE,3 / REAL,2 / MAT,1
ASEL,S,LOC,Y,h_lower
NSLA,S,1 / ESLN,S / ESURF
TYPE,2 / REAL,2 / MAT,1
ASEL,S,LOC,Y,h_lower+initial_gap
NSLA,S,1 / ESLN,S / ESURF

Confirm that n_conta and n_targe are > 0 before continuing.

CONTA174 and TARGE170 elements at the interface after ESURF — Figure 3. Contact and target elements created with `ESURF` on the selected faces.

Step 3 — CNCHECK and initial state

Open gap, closure, and interference — Figure 4. Three states: open gap, displacement-driven closure, and initial interference.

/SOLU
NLGEOM,ON
CNCHECK,AUTO

Read the .out file: minimum gap, reported penetration, and initially open or closed pairs.

Step 4 — Solve, POST1, and CSV

CMSEL,S,bottom_nodes / D,ALL,ALL,0
CMSEL,S,top_nodes
D,ALL,UY,disp / D,ALL,UX,0 / D,ALL,UZ,0
AUTOTS,OFF / KBC,0 / NSUBST,10 / SOLVE

In POST1, sum RFY at the lower support. Write m11_contact_audit.csv with contact_closed, force_error, and n_converged. Measured reference: rfy_close ≈ 5.65 MN, study_passes = 1.

Bug hunt

Five scenarios documented in 11_bug_hunt.mac:

Contact and target surfaces swapped.
ESURF without a prior selection → n_conta = 0.
Omitting CNCHECK → undocumented initial state.
Incorrect TYPE/REAL while creating surface elements.
Accepting SOLVE without reading reactions or contact state.

Verifiable challenge — Friction or modified gap

After validating the base deliverable, choose Challenge A (add friction with KEYOPT,2,12,1 and MP,MU) or Challenge B (increase the gap to 1 mm and adjust displacement). Predict the change in RFY or contact_closed before running.

Self-assessment

Quick questions

What does CNCHECK report that does not appear in an analysis without contact?
Why do we constrain UX and UZ on the upper face while the gap is open?
When would you use friction instead of the frictionless base deliverable?

Learning evidence

m11_contact_audit.csv — three cases with passes=1.
m11_summary.csv — study_passes=1.
Excerpt from the .out file containing CNCHECK output.
Brief note explaining gap versus penetration versus closure.

Exit checklist

CONTA/TARGE pair with consistent 16+16 counts.
CNCHECK run before each SOLVE.
Case 1: contact_closed = 0.
Case 2: contact_closed = 1 and rfy_close ≈ 5.65 MN.
Case 3: documented initial penetration of 0.1 mm.
study_passes=1 in a clean run.

Technical traceability

Commands: CONTA174, TARGE170, ESURF, REAL, KEYOPT, CNCHECK, NLGEOM, NSUBST, *GET. Reference: Contact Technology Guide. Inherited from: M10 (substeps, NLGEOM). Next: M12 idealized bolted joints with CERIG.

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