Tension and compression diagrams for sandstone

Conclusions

• 1. Tension and compression diagrams show that sandstones from the “Zagadka” bed and Arkagalinsk deposit, with different petrographic structure, have deformation curves which express different relations between E and σ.

• 2. For the specimens which we tested, repeated loading and unloading increases the steepness of the loading branch and has little effect on the unloading branch. This effect is very marked for Zagadka sandstone, but less so for Arkagalinsk sandstone.

• 3. Under loading, the deformation curves for Zagadka sandstone under tension and compression tend in opposite directions; the tension curve is convex towards the σ axis, while the compression curve is convex towards the ε axis. It follows that under tension E for the Zagadka sandstone decreases with rise of stress, but under compression it increases. For Arkagalinsk sandstone the loading branches of the tension and compression diagrams are almost straight.

• 4. During unloading, the deformation curves for tension and compression are convex towards the ε axis. Thus the deformation coefficient increases with the stress. This relation is less marked for Arkagalinsk sandstone.