AbstractA modified drop‐shatter test apparatus was used to study the primary breakage of particles of two solid fuels. In this apparatus many particles could be subjected to just one impact under known conditions.About 100000 particles of each fuel, sorted by size and shape into eight separate groups, were dropped from four different heights and the fragments thus formed were sifted to determine their size distributions, that is the experimental breakage functions.The interior of particles, of regular or irregular shape, fails under tension and the resulting fragmentation is due to stress‐activated volume flaws which give rise to coarse fragments whose distribution can be represented by a theoretical breakage function of the form\documentclass{article}\pagestyle{empty}\begin{document}$$ B(z) = \mathop \Sigma \limits_{{\rm \gamma = 1}}^\infty \left[ {\frac{{\lambda \cdot e^{ - \lambda } }}{{{\rm \gamma !(1 - }e^{ - \lambda } )}} \cdot \left\{ {1 - (1 + {\rm \gamma }z^3 )(1 - z^3 )^{\rm \gamma } } \right\}} \right] $$\end{document}wherezis the relative size of the fragments and γ is the number of stress‐activated volume flaws per particle.The average values of γ, given by μγ= λ/(1 – e−λ), ranged from about one to five, corresponding to the formation of two to six coarse fragments per broken particle.The probability of breakage was log‐norma