`Engineering' versus `true' stress and strain
| Species (N) . | Maximum `engineering' stress (MPa) . | Maximum `true' stress (MPa) . | Δ . | `Engineering' strain at failure . | `True' strain at failure . | Δ . |
|---|---|---|---|---|---|---|
| Geukensia demissa (19) | 75.1±10.4 | 140.8±18.7 | +88% | 0.897±0.034 | 0.637±0.018 | –29% |
| Modiolus modiolus (20) | 161.3±19.8 | 287.8±35.6 | +78% | 0.781±0.045 | 0.571±0.024 | –27% |
| Mytilus californianus (21) | 111.0±11.7 | 215.3±25.3 | +94% | 0.901±0.032 | 0.639±0.016 | –29% |
| Mytilus edulis (25) | 109.2±8.6 | 216.9±18.8 | +99% | 0.958±0.034 | 0.669±0.017 | –30% |
| Species (N) . | Maximum `engineering' stress (MPa) . | Maximum `true' stress (MPa) . | Δ . | `Engineering' strain at failure . | `True' strain at failure . | Δ . |
|---|---|---|---|---|---|---|
| Geukensia demissa (19) | 75.1±10.4 | 140.8±18.7 | +88% | 0.897±0.034 | 0.637±0.018 | –29% |
| Modiolus modiolus (20) | 161.3±19.8 | 287.8±35.6 | +78% | 0.781±0.045 | 0.571±0.024 | –27% |
| Mytilus californianus (21) | 111.0±11.7 | 215.3±25.3 | +94% | 0.901±0.032 | 0.639±0.016 | –29% |
| Mytilus edulis (25) | 109.2±8.6 | 216.9±18.8 | +99% | 0.958±0.034 | 0.669±0.017 | –30% |
Values given are means ± s.e.m. For both stress and strain and for all species, `true' values were significantly different from `engineering'values, allowing us to reject the hypothesis that changes in thread area and length during the testing procedure were insignificant (paired t-test: P<0.0001; paired sign test: P<0.0001). Note that the discrepancy (Δ) between`engineering' and `true' values increases as strain at failure increases