Influence of pre-stretching on the tensile strength,fatigue properties and the in-plane anisotropy in Al-Cu-Li alloy AA2099

The influence of pre-stretching prior to artificial aging on microstructure,tensile properties,and fatigue behavior of AA2099-T8 sheets was investigated.The results showed that increased pre-strain level from 1%to 6%resulted in a more uniform distribution and increasing density of the T_(1)phase.The localized plastic deformation during pre-stretching led to the formation of dense precipitation bands(DPBs)and precipitation free bands(T_(1)-PFBs)in the sheets with the 1%pre-strain.The non-uniform distribution of the T_(1)phase with T_(1)-PFBs and DPBs resulted in a decrement in elongation and a strong in-plane anisotropy of tensile properties.An appropriate level of pre-strain should be executed aiming to improve elongation and reduce the tensile anisotropy by promoting a uniform distribution of the T_(1)phase.In-plane anisotropy of yield strength due to the presence of DPBs and T_(1)-PFBs was quantitatively analyzed by the modified Hall-Petch formula.The results of the calculation for the modified model showed good agreement with the experiment.In addition,resistances of fatigue crack propagation(FCP)in the same orientation were gradually decreased with the increment of pre-strain due to the increment in yield strength and more uniform distribution of the T_(1)phase.For the in-plane anisotropy of FCP resistance,the main reasons were the development of rough fracture surfaces and the transgranular fracture modes in L-T orientation.

Theoretical perspective on synthetic man-made life:Learning from the origin of life

Creating a man-made life in the laboratory is one of life science's most intriguing yet challenging problems.Advances in synthetic biology and related theories,particularly those related to the origin of life,have laid the groundwork for further exploration and understanding in this field of artificial life or man-made life.But there remains a wealth of quantitative mathematical models and tools that have yet to be applied to this area.In this paper,we review the two main approaches often employed in the field of man-made life:the top-down approach that reduces the complexity of extant and existing living systems and the bottom-up approach that integrates welldefined components,by introducing the theoretical basis,recent advances,and their limitations.We then argue for another possible approach,namely"bottom-up from the origin of life":Starting with the establishment of autocatalytic chemical reaction networks that employ physical boundaries as the initial compartments,then designing directed evolutionary systems,with the expectation that independent compartments will eventually emerge so that the system becomes free-living.This approach is actually analogous to the process of how life originated.With this paper,we aim to stimulate the interest of synthetic biologists and experimentalists to consider a more theoretical perspective,and to promote the communication between the origin of life community and the synthetic man-made life community.