Polymer Bearing Load Capacity and Stiffness Calculator

Content

Estimate static radial load capacity, elastic stiffness, contact pressure, and contact geometry for polymer bearing bushes and guide rings.

Engineering screening tool—verify inputs and results independently. Use at your own risk.

Model inputs

Choose whether pressure or indentation controls the calculation, then enter positive dimensions and material data.

Screening result

Static elastic response at the entered pressure or indentation.

Pressure limit controls indentation

Load capacity F735.23N
Stiffness F/δ73.52 MN/m
Average pressure F/(LD)1.84 MPa
Mean contact pressure5.97 MPa
Maximum pressure9.00 MPa
Indentation δ/s0.50 %
Semi-contact ratio b/R0.31 —
Contact angle φ35.14 deg

Pressure limits for polymers depend strongly on temperature, duration, moisture, manufacturing history, and allowable creep. Confirm material data independently.

How to use

  1. Select Pressure-limited bearing to derive indentation from an allowable maximum pressure, or Guide ring by indentation to derive pressure from a prescribed compression ratio.
  2. Enter shaft or piston diameter D, axial bearing length or ring width L, polymer wall thickness s, and nonnegative radial clearance dR in millimetres.
  3. Enter the effective compressive elastic modulus E in MPa. Use representative temperature-, rate-, moisture-, and confinement-conditioned data when available.
  4. Enter pmax in MPa for pressure-limited mode or δ/s in percent for indentation-controlled mode. All dimensional values must be finite and positive; clearance may be zero.
  5. Select Calculate to update the single result panel. Reset restores pressure-limited defaults.
  6. Interpret F as a static screening load, F/δ as secant stiffness, and the pressure/contact metrics as model outputs—not material allowables.
  7. Do not use this model for creep life, impact, edge loading, misalignment, thermal expansion, wear, dynamic PV limits, or geometry with H ≥ 2. Use a detailed contact/material analysis instead.

Worked example

1. Select pressure-limited mode and enter D = 20 mm, L = 20 mm, s = 2 mm, E = 1800 MPa, dR = 0.2 mm, and pmax = 9 MPa.

Bruker

2. Calculate. The expected load is 735.23 N, stiffness is 73.52 MN/m, average projected pressure is 1.84 MPa, and contact angle is 35.14°.

3. This means the idealized ring supports about 0.735 kN at the entered local pressure limit under the stated elastic assumptions. It is not a service-life or creep rating.

Equations used

All equations use SI base units internally. Compression and pressure are positive; radial clearance is nonnegative.

R = D/2; C = dR/RPressure-limited mode: ε = δ/s = pmax/EIndentation-controlled mode: pmax = εEδ = εs; H = δ/R, with 0 < H < 2b/R = √[H(2 − H)(H + 2C)(H + 2C + 2)] / [2(C + H)]φ = 2 asin[(b/R)/(1 + C)]p̄ = (ED/4s){(C + H)cos(φ/2)sin(φ/2) + (C + H)φ/2 − 2C sin(φ/2)}F = p̄LD; pm = p̄/(b/R); stiffness = F/δ

Symbols: D is shaft/piston diameter; R is radius; L is axial loaded length; s is polymer wall thickness; dR is radial clearance; C is normalized clearance; E is effective compressive modulus; δ is center indentation; ε is indentation ratio; H is normalized indentation; b is contact semi-width; φ is contact angle in radians inside the equations; p̄ is projected-area pressure; pm is mean contact pressure; pmax is local maximum pressure; and F is load. Displayed contact angle is converted to degrees.

Theory and method

The model treats the polymer element as an elastically compressed cylindrical ring. Clearance and indentation define the contact half-width and angular extent; integrating the idealized pressure field gives projected-area pressure, load, and secant stiffness. The two modes use the same contact equations and differ only in whether pmax or ε is prescribed.

RdR2bBlue: shaft / pistonGray: polymer wall sGreen: loaded contact arc φGap closes by indentation δ
Polymer bearing contact geometry. The model assumes uniform axial loading, plane strain, and zero wear.

Input definitions and limits

  • D, L, s: finite positive dimensions in mm. D = 2R; no geometric sign reversal is allowed.
  • E: finite positive effective compressive modulus in MPa. For guide rings, it can be estimated from a representative compressed strip as E = p/(δ/s).
  • dR: finite radial clearance in mm, dR ≥ 0.
  • pmax or δ/s: finite positive control input. The geometry requires H < 2; the interface enforces pmax/E < 2 or δ/s < 200%.

Assumptions and applicability

Static elasticity, plane strain, zero wear, uniform axial conditions, and a modulus representative of the service state are assumed. Real thermoplastics are viscoelastic; time, temperature, moisture, stress concentration, tolerances, and creep can govern well below a short-term compressive strength. Validate allowables and safety factors for the intended duty.