We studied the variability in longitudinal growth strains and wood basic density in five-year old trees from five clones （one tree per clone） of Eucalyptus tereticornis. Mean longitudinal growth strain in clones ran...We studied the variability in longitudinal growth strains and wood basic density in five-year old trees from five clones （one tree per clone） of Eucalyptus tereticornis. Mean longitudinal growth strain in clones ranged from 466 to 876 μm. There was a significant difference between clones in growth strains and wood basic density. Clone 10 exhibited maximum growth strains and basic density, whereas clone 3 and clone 7 exhibited minimum growth strains and basic density, respectively. Within a tree, the growth strain variation with tree height was high but statistically insignificant while within tree variation in basic density was very small. There was no specific trend in variation in either strain or density within a tree. There was 5% 200% difference in growth strain on opposite sides of the logs. However two strains showed a strong positive correlation. There was a moderate positive association of wood basic density and mean growth strains in logs. The variation around the periphery emphasize the need to measure strain more than one, preferably on opposite sides at the same height, on a tree to know the mean strain level for the purpose of selection of clones.展开更多
Finite element computations are carried out to simulate plane strain crack growth on a bimaterial interface under the assumption of small scale yielding.The modified Guron constitutive equation and the element vanish ...Finite element computations are carried out to simulate plane strain crack growth on a bimaterial interface under the assumption of small scale yielding.The modified Guron constitutive equation and the element vanish technique introduced by Tvergaard et al.are used to model the final formation of an open crack.It is found from the calculation that the critical fracture toughness for crack growth is much low- er in bimaterials than that in homogeneous material.The critical fracture toughness is strongly dependent on material properties of the bimaterial pair and the mixed mode of remote loads.The interface crack grows in the more compliant(lower hardening)material or in the weaker(lower yield strength)material.In Mode-Ⅰ loading,the crack grows zigzag along the interface.展开更多
Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The elastic response of the vessel may become larger in a later stage compared to its response during the initial stag...Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The elastic response of the vessel may become larger in a later stage compared to its response during the initial stage. The dynamic responses of infinitely long cylindrical containment vessels subjected to uniformly-distributed internal blast loading are studied using LS-DYNA. The development of bending modes and the interaction between the breathing mode and bending modes are observed. The methodology developed for dynamic elastic buckling analysis is employed to study the strain growth phenomenon in explosion containment vessels. It is shown that the dynamic instable vibration of a containment vessel is the basic mechanism of strain growth.展开更多
The longitudinal displacement between two reference points upon stress release was measuredthrogh using the CIRAD-forêt one-hole method on a total of 305 trees of 6 eucalyptuses, includingEucalyptus urophylla, E....The longitudinal displacement between two reference points upon stress release was measuredthrogh using the CIRAD-forêt one-hole method on a total of 305 trees of 6 eucalyptuses, includingEucalyptus urophylla, E. pellita, E. teriticornis, E. camaldulensis, E. urophylla × E. grandis and E.urophylla × E. teriticornis. These trees were between 3 to 5 years old and are regarded as commerciallyimportant plantation species in China. Significant differences in the growth strain and diameter atbreast height over bark (DBHOB) were observed between species, provenances and clones of thesame age. The data clearly showed that, E. pellita, E. teriticornis and E. camaldulensis (provenance15025) had higher growth rates but much lower growth strain at the tree surface, in comparison to otherspecies / hybrids / clones. Whilst conclusive recommendations for species selection need to besubstantiated with comprehensive studies that include other key wood properties, results of this studyhave shown trends pertaining to wood quality differences between the six species.展开更多
The influences of pre-strain on the mechanical property and fatigue crack growth of 2E12 aluminum alloy were evaluated by SEM,TEM,mechanical property and fatigue tests. The axial fatigue tests were conducted under a c...The influences of pre-strain on the mechanical property and fatigue crack growth of 2E12 aluminum alloy were evaluated by SEM,TEM,mechanical property and fatigue tests. The axial fatigue tests were conducted under a constant amplitude sinusoidal wave loading at stress ratio of 0.1 in laboratory air and salt fog at room temperature. The results show that the yield stress of pre strain material is higher than that of the material without undergoing pre-strain,but pre-strain can not make the increase of the growth rate of fatigue crack. Fatigue crack growth rates of the alloy in salt fog are higher than those in air. The increased fatigue crack growth of the alloy in a given environment and more brittle striations can be observed in salt fog.展开更多
文摘We studied the variability in longitudinal growth strains and wood basic density in five-year old trees from five clones （one tree per clone） of Eucalyptus tereticornis. Mean longitudinal growth strain in clones ranged from 466 to 876 μm. There was a significant difference between clones in growth strains and wood basic density. Clone 10 exhibited maximum growth strains and basic density, whereas clone 3 and clone 7 exhibited minimum growth strains and basic density, respectively. Within a tree, the growth strain variation with tree height was high but statistically insignificant while within tree variation in basic density was very small. There was no specific trend in variation in either strain or density within a tree. There was 5% 200% difference in growth strain on opposite sides of the logs. However two strains showed a strong positive correlation. There was a moderate positive association of wood basic density and mean growth strains in logs. The variation around the periphery emphasize the need to measure strain more than one, preferably on opposite sides at the same height, on a tree to know the mean strain level for the purpose of selection of clones.
基金Project supported by Fok Ying-Tung Education Foundation National Natural Science Foundation of China.
文摘Finite element computations are carried out to simulate plane strain crack growth on a bimaterial interface under the assumption of small scale yielding.The modified Guron constitutive equation and the element vanish technique introduced by Tvergaard et al.are used to model the final formation of an open crack.It is found from the calculation that the critical fracture toughness for crack growth is much low- er in bimaterials than that in homogeneous material.The critical fracture toughness is strongly dependent on material properties of the bimaterial pair and the mixed mode of remote loads.The interface crack grows in the more compliant(lower hardening)material or in the weaker(lower yield strength)material.In Mode-Ⅰ loading,the crack grows zigzag along the interface.
文摘Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The elastic response of the vessel may become larger in a later stage compared to its response during the initial stage. The dynamic responses of infinitely long cylindrical containment vessels subjected to uniformly-distributed internal blast loading are studied using LS-DYNA. The development of bending modes and the interaction between the breathing mode and bending modes are observed. The methodology developed for dynamic elastic buckling analysis is employed to study the strain growth phenomenon in explosion containment vessels. It is shown that the dynamic instable vibration of a containment vessel is the basic mechanism of strain growth.
文摘The longitudinal displacement between two reference points upon stress release was measuredthrogh using the CIRAD-forêt one-hole method on a total of 305 trees of 6 eucalyptuses, includingEucalyptus urophylla, E. pellita, E. teriticornis, E. camaldulensis, E. urophylla × E. grandis and E.urophylla × E. teriticornis. These trees were between 3 to 5 years old and are regarded as commerciallyimportant plantation species in China. Significant differences in the growth strain and diameter atbreast height over bark (DBHOB) were observed between species, provenances and clones of thesame age. The data clearly showed that, E. pellita, E. teriticornis and E. camaldulensis (provenance15025) had higher growth rates but much lower growth strain at the tree surface, in comparison to otherspecies / hybrids / clones. Whilst conclusive recommendations for species selection need to besubstantiated with comprehensive studies that include other key wood properties, results of this studyhave shown trends pertaining to wood quality differences between the six species.
基金Projects(2005CB623705) supported by the National Basic Research Foundation of China
文摘The influences of pre-strain on the mechanical property and fatigue crack growth of 2E12 aluminum alloy were evaluated by SEM,TEM,mechanical property and fatigue tests. The axial fatigue tests were conducted under a constant amplitude sinusoidal wave loading at stress ratio of 0.1 in laboratory air and salt fog at room temperature. The results show that the yield stress of pre strain material is higher than that of the material without undergoing pre-strain,but pre-strain can not make the increase of the growth rate of fatigue crack. Fatigue crack growth rates of the alloy in salt fog are higher than those in air. The increased fatigue crack growth of the alloy in a given environment and more brittle striations can be observed in salt fog.
