Stress and Strain

Engineering stress σ=F/A uses the initial area; measured engineering strain ε=ΔL/L uses initial length. Positive F and ΔL mean tension/elongation, negative values compression/shortening. Secant σ/ε is the ratio of one measured point, not a measured tangent modulus. It is undefined when strain is zero and may disagree with the separately supplied positive E. Linear prediction ΔL=σL/E uses Hooke’s law with constant E and small deformation, not plasticity.

The reference quotient is σref/|σ|. It is a magnitude comparison with your entered reference, not an automatic safety factor, yield prediction or design approval. Choose a value appropriate to tensile/compressive loading. Material presets are illustrative values, not certified grades; concrete and pine examples refer to compression, with direction/material variability requiring your own reference. Work density½σε and work½σεAL assume a linear monotonic path from the origin and matching stress/strain signs; otherwise unavailable (—). Zero load makes the reference quotient undefined. Inputs use N,mm²,m,mm,GPa,MPa and convert internally to SI. The default measurement is consistent with E=200GPa. Settings survive navigation/reload. Numerical over/underflow is rejected, not printed as infinity or a false zero.