Size effects (SEs) impede the mass production of high-performance miniaturised components via micro-forming. Although many studies have examined SEs from multiple aspects, such as flow stress, deformation, and ductile fracture, the SE transitions characterised by the significant changes of these phenomena across the micro- and macroscale remain ambiguous. These SE transitions must be fully and deeply explored to enable the transformation of microscale deformations to macroscale ones by the design of products with appropriate dimensions, grain sizes and loading boundaries. This study involved experimental and numerical studies of multi-aspect SE transitions in flow stress, heterogeneous deformation (surface roughening and strain localisation) and ductile fracture at the micro- and macroscale in copper (Cu) sheets, which are widely used in electronic industries. The Cu sheets for tensile tests were designed and fabricated to be with a thickness (t) of 0.05–1.50 mm, a grain size (d) of 3–260 μm and t/d of 0.63–65.30. The crystal plasticity finite element model (CPFEM) and the Voronoi-based polycrystalline geometric model (VPGM) with t/d of 1–30 were established. Compared with the phenomenological work hardening model (PM), the dislocation density-based model (DDBM) can better predict the multi-aspect behaviours within the scope of above-mentioned scales. An obvious SE transition point (λ) was observed: when t/d < λ, there is a sharp decrease in materials strength and necking strain, an increase in surface roughness and a transformation of fracture mode, as well as a remarkable scattering of the aforementioned responses. The SE transition points vary from t/d = 3 to 11 for different responses, and generally the stress-related λ is smaller than the strain-related one. The larger the t/d, the closer the stress and strain distributions are to the normal distribution. The distribution irregularity of grain-scale stress to the change of t/d is more sensitive than that of strain. Different distributions in grain orientations are the primary inducers of this scattering of responses when t/d < λ. Grain-scale deformation heterogeneity and scattering could be decreased through controlling scale factor t/d > λ, thereby entering the macroscale deformation domain. Case studies of micro-pin extrusion and thin-walled tube-drawing confirmed that setting t/d > λ or using a boundary constraint could alleviate the negative influences of SEs, thus enabling a more uniform deformation.

尺寸效应 (SE) 阻碍了通过微成型大规模生产高性能小型化组件。尽管许多研究已经从流动应力、变形和韧性断裂等多个方面研究了 SE，但以这些现象在微观和宏观尺度上的显着变化为特征的 SE 转变仍然模棱两可。必须对这些 SE 转变进行全面而深入的探索，以通过设计具有适当尺寸、晶粒尺寸和负载边界的产品来实现微观变形向宏观变形的转变。这项研究涉及在铜 (Cu) 片材的微观和宏观尺度上流动应力、异质变形（表面粗糙化和应变局部化）和韧性断裂的多方面 SE 转变的实验和数值研究，广泛应用于电子行业。用于拉伸试验的铜板被设计和制造成厚度为（t ) 为 0.05–1.50 mm，晶粒尺寸 ( d ) 为 3–260 μm，t/d为 0.63–65.30。建立了t/d为1~30的晶体塑性有限元模型（CPFEM）和基于Voronoi的多晶几何模型（VPGM）。与唯象加工硬化模型（PM）相比，基于位错密度的模型（DDBM）可以更好地预测上述尺度范围内的多方面行为。观察到明显的 SE 转变点 ( λ )：当t/d < λ 时，材料强度和颈缩应变急剧下降，表面粗糙度增加和断裂模式的转变，以及上述响应的显着分散。对于不同的响应， SE 转变点从t/d  = 3 到 11 不等，通常与应力相关的λ小于与应变相关的 λ。t/d越大，应力和应变分布越接近正态分布。晶粒尺度应力分布的不规则性对t/d的变化比应变的变化更为敏感。当t/d < λ时，晶粒取向的不同分布是这种响应散射的主要诱因. 通过控制尺度因子t/d > λ可以降低晶粒尺度变形的不均匀性和散射，从而进入宏观尺度变形域。微针挤压和薄壁管拉伸的案例研究证实，设置t/d > λ或使用边界约束可以减轻 SE 的负面影响，从而实现更均匀的变形。