2. Property dispersal: an inescapable reality

The many parameters involved in polymer and additive production, blending, plastics processing and the use of parts and products result in a statistical distribution of properties that is all the more important the more complex the material.

Table 1 compares the statistical distributions of the breaking strengths of one steel and two thermoplastics:

• average μ ;

• standard deviation σ ;

• coefficient of variation C _v defined as the ratio between the standard deviation (σ) and the mean μ: C _v = σ/μ ;

• 95% confidence interval, i.e. two standard deviations either side of the...