Viscoplastic Constitutive Modeling of Strain Hardening and Thermal Softening Interplay
Coupled viscoplastic modeling of back-stress hardening and adiabatic softening allows thin-wall tooling optimization that cuts cycle times and capital spend.
ISO 604
Meaning
Standardized test methodology determining the compressive properties of rigid and semi-rigid plastics establishes uniform procedures for measuring modulus, yield stress and nominal compressive strain. Under the rules of ISO 604, small prisms or cylinders experience uniaxial loading along their primary axis at constant displacement rates. The protocol applies to unreinforced, filled and reinforced thermoplastic compounds alongside thermosetting resins.
It ceases to apply to flexible cellular materials or rubber elastomers, which require dedicated compressive deflection testing procedures.
Specimen Geometry
Test coupon dimensions strictly determine the validity of the resulting stress-strain curves by preventing mechanical buckling. In testing under ISO 604, standard specimens are rectangular prisms measuring ten by ten by four millimetres for modulus determination, or elongated prisms measuring fifty millimetres in height for ultimate strength evaluations. Precise machining or defect-free injection moulding is required because non-parallel load surfaces induce unaxial bending moments.
End-face friction between the specimen and metal platens generates barrel distortion, which restricts lateral expansion and inflates apparent compression values. Extensometers attached directly to the gauge area bypass platen displacement errors, isolating pure material deformation.
Mechanical Determination
Compressive yield values obtained from this protocol reveal how structural resin handles heavy clamping forces and stacking loads. Testing under ISO 604 produces a compressive modulus calculated from the slope between zero-point-zero-five percent and zero-point-two-five percent strain. Virgin resins exhibit well-defined yielding followed by plastic flow or brittle shear fracture along diagonal slip planes.
Blends containing high regrind content often show premature shear failure under compression due to internal micro-voids and degraded molecular weight. While tensile datasheets are frequently used for structural part sizing, plastic parts under flexure fail first along their compressive face, making compressive yield figures critical for collapse calculations.
Moulding Influence
Specimen fabrication processes directly dictate the scattering of compressive test outcomes across production batches. Injection moulded coupons feature anisotropic properties driven by molecular orientation along the cavity filling vector. ISO 604 specimens cut parallel to flow exhibit higher compressive yield points than those cut perpendicular to flow.
Low holding pressure leaves core porosity that collapses under load, manifesting as an artificially reduced compressive modulus. Gate locations that create weld lines within the central gauge region cause early compressive buckling or brittle splitting along the knit boundary. Consistent barrel melt temperatures and sufficient pack times ensure solid cross sections necessary for reproducible compressive metrics.
ISO 604 provides the fundamental baseline for evaluating the crushing capacity of load-bearing polymer structures.