Compressive Strength

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Compressive strength

Definition of compressive strength

The compressive strength σ_M or σ_cM is determined in a compression test on rigid and semi-rigid plastics, i.e. thermoplastic injection moulding and extrusion materials, fibre-reinforced moulding compounds, and unreinforced and reinforced thermosetting plastics in accordance with DIN EN ISO 604 [1]. By definition, compressive strength is the maximum compressive stress that the test specimen can withstand during a compression test. The compressive strength is calculated according to Eq. (1) at the absolute maximum force in the test, whereby A₀ is used instead of A in the standard for the initial cross-sectional area.

$\sigma _{m}\ ={\frac {F_{m}}{A_{0}}}={\frac {F_{max}}{A_{0}}}$

(1)

Compressive stress-strain curves of plastics

Figure 1 shows a schematic compressive stress-strain curve from which the typical measured variables can be derived.

Fig. 1:

Typical compressive stress-strain curves for plastics in compression testing according to [1]

The relative maximum force in curve a of Figure 1 is referred to as the pressure yield stress σ_y. The deformation value associated with compressive strength is the nominal compression at compressive strength ε_cM, which is derived from Eq. (2).

$\varepsilon _{cM}\ ={\frac {\Delta L_{cM}}{L}}$

(2)

L is the initial distance between the pressure plates (see compression test arrangement).

Typical compressive strength values for plastics

A comprehensive literature analysis of the mechanical characteristics σ_M and σ_y, determined in compression tests, is compiled for numerous plastics in [2].

See also

• Compression test arrangement
• Compression test
• Compression test compliance
• Strength
• Creep compression test
• Compression after impact test

References

[1]	ISO 604 (2002-03): Plastics – Determination of Compressive Properties
[2]	Bierögel, C., Grellmann, W.: Compression loading. In: Grellmann, W., Seidler, S.: Mechanical and Thermomechanical Properties of Polymers. Landolt-Börnstein. Volume VIII/6A3, Springer, Berlin (2014) 150–163, (ISBN 978-3-642-55165-9; siehe AMK-Library under A 16)