The Journal of Strain Analysis for Engineering Design

The fracture toughness of mild steels was successfully determined under monotonic and cyclic crack propagation. The conditions governing the valid measurement of fracture toughness were satisfied by r.d.c.b. (reinforced-double-cantilever-beam) specimens, and photomicrographic evidence and compliance measurements verified the yielding of the specimens during cracking confined to the crack tip. Measurements of fracture toughness of EN 24 (BS 970 817M40) steel were made on the r.d.c.b., c.o.d. (crack-opening displacement) and c.k.s. (standard tension testing) specimens and the results verified the validity of the r.d.c.b. testing method. The compliance measuring approach was used to determine the rate of fatigue crack propagation and was found satisfactory using the graphical representation based on change in crack extension force ΔG. It was observed that the grain size of the steel has definite effects on its fracture toughness.

The bending stresses in thin circular plates having a single eccentric circular hole and small deflections are reported. The plates can have any mixture of clamped and simply supported boundaries, and can be subjected to a concentrated force uniformly distributed round the inner boundary, moments about two perpendicular axes, or uniform pressure on the plate surface. A previous paper (1)∗ has described the method of analysis using bipolar co-ordinates, and has given values for deflection and slope coefficients for varying diameter ratios and eccentricities under the loads described above. The present paper discusses the stresses found in the plates under the same conditions.

Tests have been carried out to determine the strength of balsa wood and its variation with density. Particular attention is paid to the tensile strength of balsa loaded at different angles to the grain and a simple theory of failure is derived from the results. The compressive strength and modulus of elasticity are also reported. Similarities between the mechanical behaviour of balsa wood and unidirectional fibre-reinforced composites are discussed. Adequate data are presented for the design of balsa wood structures.

A preliminary investigation of the influence of rest periods on Stage I crack growth has been performed on a 2½ per cent Ni Cr Mo steel by testing cylindrical specimens under high-strain reversed torsion conditions at 20, 100, 200, 300 and 400°C. Increases in lifetime of up to 100 per cent are observed, and their magnitude is a function of temperature and the rest-period duration, with maximum lifetime occurring at 300°C and a total rest period of 20 hours. Strain ageing is cited as the dominant process, which explains the dependence of optimum lifetime conditions on both temperature and total rest period duration.

Since components are frequently rested and/or subjected to variable strain-rate conditions over a range of temperatures, it is suggested that results obtained from uninterrupted laboratory tests may be conservative unless overageing occurs leading to cyclic softening.