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In this work stress concentration factors, Kt , for a round bar with a circular‐arc or V‐shaped notch are considered on the basis of exact solutions for special cases and accurate numerical results. Then, a set of Kt formulae useful for any shape of notch is proposed. The conclusions can be summarized as follows. (i) For the limiting cases of deep (d) and shallow (s) notches, the body force method is used to calculate the Kt values. Then, the formulae are obtained as Ktd and Kts . (ii) On the one hand, upon comparison of Kt  and Ktd it is found that Kt is nearly equal to Ktd if the notch is deep or blunt. (iii) On the other hand, if the notch is sharp or shallow, Kt is mainly controlled by Kts and the notch depth. (iv) The notch shape is classified into several groups according to the notch radius and notch depth. Then, the least‐squares method is applied for the calculation of Kt /Ktd and Kt /Kts . (v) Finally, a set of convenient formulae is proposed that are useful for any shape of notch in a round test specimen. The formulae give SCFs with <1% error for any shape of notch.

The phenomenon of herding is a very general feature of the collective behavior of many species in panic conditions, including humans. It has been predicted theoretically that panic-induced herding in individuals confined to a room can produce a nonsymmetrical use of two identical exit doors. Here we demonstrate the existence of that phenomenon in experiments, using ants as a model of pedestrians. We show that ants confined to a cell with two symmetrically located exits use both exits in approximately equal proportions to abandon it in normal conditions but prefer one of the exits if panic is created by adding a repellent fluid. In addition, we are able to reproduce the observed escape dynamics in detail using a modification of a previous theoretical model that includes herding associated with a panic parameter as a central ingredient. Our experimental results, combined with theoretical models, suggest that some features of the collective behavior of humans and ants can be quite similar when escaping under panic.

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