Abstract—The plastic work to propagate a fatigue crack by a unit area,U, measured by the foil strain gage technique requires an extrapolation to estimate the contribution closer than 100 μm to the crack tip. This is due to the size of the strain‐gages used, 200 × 210 μm. Conversely, the electron channeling technique for determiningUis useful mainly close to the crack tip where subgrains form. In the present workUwas measured by both techniques in the same low carbon steel at ΔK= 8 MN/m3/2. The contribution toUfrom closer than 100 μm of the crack tip was determined to be 1·7 × 106J/m2using electron channeling and 2·0 × 106J/m2by extrapolation. The measured contribution toUfrom further than 100 μm from the crack tip was 3·6 × 106J/m2giving 5·3 × 106J/m2forU.Thus, a large amount of energy is absorbed outside the region where sub‐grains form. The non‐hysteretic plastic work was found to be about four orders of magnitude smaller than the hysteretic plastic work, and may be neglected. A map of the plastic zone results from the strain‐gage measurement. Rice's theory predicts the measured plastic zone sizeif the proper material's strength is