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• +Insights into the helium bubbles coarsening behavior in the post irradiated annealing 304L stainless steel processed by laser powder bed fusion

  350 keV He + ions were injected into laser powder bed fusion (LPBF) processed 304L stainless steel andtraditional rolled 304L stainless steel with a flux of 1 × 10 17 ions/cm 2 at room temperature and followed byannealing at 750 °C for 10 and 100 h and 300h, respectively. The results showed that the material swellingdue to helium bubbles coarsening was almost not observed in both the LPBF and rolled samples after 10 hoursof annealing duration. A rapid coarsening and swelling of bubbles occurred in rolled samples but only moderate bubbles growth in the LPBF sample after annealing for 100 hours. After annealing for 300h, the heliumbubbles of both samples tend to grow steadily. For 10 hours of annealing, the irradiated samples were in disequilibrium state and the apparent activation energy (E act ) calculated by Arrhenius model determines that heliumatoms tended to diffuse through the displacement mechanism, and helium bubbles grew under the migration andcoalescence (MC) mechanism. With the annealing time over 100 hours, the high-density dislocations and thenano-oxide particles in LPBF sample still had a strong trapping effect on helium bubbles moving and growth.After annealing for 300 hours, the cellular subgrains in the LPBF sample decomposed, and the nano oxide particles had no trapping effect on the helium bubbles. At this time, the dislocation structure played the primary rolein suppressing the helium bubbles growth, and the radiation resistance of the LPBF sample remained superiorto that of rolled samples.

  Qiu,Siyi;Gu,Yanlin;Guo,Yuyu;Liu,Hui;Huang,Lei;Huang,Aijun;Hou,Juan发表时间：2024-09-12

• Insights into the in-situ ODS 304L stainless steel processed by laser powder bed fusion through oxygen content regulation and the effect on microstructure and mechanical properties

  Laser powder bed fusion (LPBF) is a widely used and well-developed additive manufacturing approach. To meet the higher material performance requirements for the fourth-generation nuclear power reactors, LPBF processing combined with oxide dispersion strengthening (ODS) is currently of interest among new materials designs and developments by dispersing nanoscale Y2O3 particles into the feeding powders to obtain the LPBF- ODS materials. Oxygen exposure and its introduction in the solvation cell, on the other hand, are usually considered detrimental but impossible to eliminate completely during the LPBF process. The understanding of this unavoidable process, however, is still limited. Here we develop a new LPBF-ODS design approach based on in-situ oxygen content regulation during the LPBF process. The oxygen content of the environment chamber was artificially adjusted through an online monitoring system to activate the reaction between oxygen and metal elements, thus forming the dispersed oxide particles in situ. Four batches of LPBFed 304L stainless steel samples were successfully processed under different oxygen levels to investigate the reinforcing effect of in-situ chemical alloying. The results show that the dispersed oxide particles are formed through the LPBF in- situ alloying approach with an average nanoscale dimension of approximately 46 nm. The number density of oxide particles increases to 11.4 particles /μm2 with the increase in oxygen content, playing a role in refining and stabilizing the cellular structure. The in-situ alloyed ODS material exhibits enhanced yield strength (up to ∼ 675 MPa) while keeping ductility not heavily affected (elongation up to ∼ 39%), which is competitive within the range of tensile properties reported for ODS alloys prepared by mechanical alloying (MA). This study analyzes the main mechanism of yield strength enhancement through the interaction between the nano- scale oxide particles and dislocation entanglement cells, providing a new idea for the subsequent preparation of high-performance LPBF-ODS alloys.

  Gu,Yanlin;Yang,Fan;Guo,Yuyu;Yan,Zhen;Huang,Aijun;Hou,Juan发表时间：2024-09-12

• iFSD: Ego-Centric Fully Sparse Paradigm with Uncertainty Denoising and Iterative Refinement for Efficient End-to-End Self-Driving

  urrent end-to-end autonomous driving methods resort to unifying modular designs for various tasks (e.g. perception, prediction and planning). Although optimized in a planning-oriented spirit with a fully differentiable framework, existing end-to-end driving systems without ego-centric designs still suffer from unsatisfactory performance and inferior efficiency, owing to the rasterized scene representation learning and redundant information transmission. In this paper, we revisit the human driving behavior and propose an ego-centric fully sparse paradigm, named DiFSD, for end-to-end self-driving. Specifically, DiFSD mainly consists of sparse perception, hierarchical interaction and iterative motion planner. The sparse perception module performs detection, tracking and online mapping based on sparse representation of the driving scene. The hierarchical interaction module aims to select the Closest In-Path Vehicle / Stationary (CIPV / CIPS) from coarse to fine, benefiting from an additional geometric prior. As for the iterative motion planner, both selected interactive agents and ego-vehicle are considered for joint motion prediction, where the output multi-modal ego-trajectories are optimized in an iterative fashion. Besides, both position-level motion diffusion and trajectory-level planning denoising are introduced for uncertainty modeling, thus facilitating the training stability and convergence of the whole framework. Extensive experiments conducted on nuScenes dataset demonstrate the superior planning performance and great efficiency of DiFSD, which significantly reduces the average L2 error by 66% and collisionrate by 77% than UniAD while achieves 6.9x faster running efficiency.

  Haisheng Su;Wei Wu;ewu Lu发表时间：2024-09-12

• he principle of minimum virtual work and its application in bridge engineering

  In mechanics, common energy principles are based on fixed boundary conditions. However, in bridge engineering structures, it is usually necessary to adjust the boundary conditions to make the structure’s internal force reasonable and save materials. However, there is currently little theoretical research in this area. To solve this problem, this paper proposes the principle of minimum virtual work for movable boundaries in mechanics through theoretical derivation such as variation method and tensor analysis. It reveals that the exact solution of the mechanical system minimizes the total virtual work of the system among all possible displacements, and the conclusion that the principle of minimum potential energy is a special case of this principle is obtained. At the same time, proposed virtual work boundaries and control conditions, which added to the fundamental equations of mechanics. The general formula of multidimensional variation method for movable boundaries is also proposed, which can be used to easily derive the basic control equations of the mechanical system. The incremental method is used to prove the theory of minimum value in multidimensional space, which extends the Pontryagin’s minimum value principle. Multiple bridge examples were listed to demonstrate the extensive practical value of the theory presented in this article. The theory proposed in this article enriches the energy principle and variation method, establishes fundamental equations of mechanics for the structural optimization of movable boundary, and provides a path for active control of mechanical structures, which has important theoretical and engineering practical significance.

  Xiang Lukai发表时间：2024-09-11