This paper presents the mechanical properties of composite beams additively manufactured by 3D-printing of layers of mortar on top of custom-designed (also 3D-printed) steel plates, which served as external flexural reinforcement. The mechanical performance of the composite beams was evaluated using three-point bending test. The results were compared with the data obtained from two types of reference specimens: 3D-printed beams with no external reinforcing plate, and composite beams with mortar cast (rather than 3D printed) on the top of the steel plate. Four different architectures (also referred to as configurations) were created by either 3D-printing (using two different filament orientations), casting, or a combination of both processes (referred to as a hybrid configuration). This configuration consisted of 3D-printed external walls (outline) of the beam and cast interior (infill). The effects of these architectures were investigated using both unreinforced and composite elements, in order to identify the contributions of the orientation of filaments and associated interfaces on the initiation and propagation of the cracks. Analysis of the initiation and propagation of the cracks was based on the data obtained from the digital image correlation (DIC) technique. Mechanical performance parameters that were investigated included the following: load-displacement responses, flexural stress-flexural strain responses, shear stress-shear strain responses, and the work of failure. The results of the test revealed that the incorporation of steel plates as an external reinforcement resulted in the transition from flexural to shear mode failure. In terms of flexural strength, all composite configurations demonstrated comparable performance independently of the architecture used while hybrid configuration outperformed cast composite counterparts by attaining significantly higher values of the work of failure. This indicates that hybrid elements developed enhanced energy dissipation characteristics compared to the other configurations. The results of specific modulus of rupture and shear strength obtained from unreinforced and reinforced hybrid elements, respectively, were comparable to those obtained from cast counterparts, indicating that the hybrid configuration may offer a viable alternative for the construction of structural concrete elements. Finally, the values of modulus of rupture and shear stress obtained for different configurations used in the study were compared to the design expressions in the ACI 318–19 code. It was found that hybrid elements as well as cast elements used in this study satisfy the minimum requirements and further studies at larger scales could confirm their use in structural applications.

中文翻译：

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小型 3D 打印钢砂浆复合梁的力学响应


本文介绍了通过在定制设计（也是 3D 打印）钢板顶部 3D 打印砂浆层增材制造的组合梁的机械性能，这些钢板用作外部弯曲钢筋。采用三点弯曲试验评价了组合梁的力学性能。将结果与从两种类型的参考试样获得的数据进行了比较：没有外部加强板的 3D 打印梁，以及在钢板顶部铸造砂浆（而不是 3D 打印）的组合梁。通过 3D 打印（使用两种不同的耗材方向）、铸造或两种工艺的组合（称为混合配置）创建了四种不同的架构（也称为配置）。这种配置包括梁的 3D 打印外墙（轮廓）和铸造内部（填充物）。使用未增强和复合元件研究了这些结构的影响，以确定细丝取向和相关界面对裂纹萌生和扩展的影响。裂纹的起始和扩展分析基于从数字图像相关 （DIC） 技术获得的数据。研究的机械性能参数包括：载荷-位移响应、弯曲应力-弯曲应变响应、剪切应力-剪切应变响应和失效功。试验结果表明，将钢板作为外部钢筋导致从弯曲模式失效转变为剪切模式失效。 在抗弯强度方面，所有复合材料配置都表现出与所使用的架构无关的可比性能，而混合配置通过获得明显更高的失效功值，优于铸造复合材料。这表明与其他配置相比，混合元件的能量耗散特性更强。从未增强和增强混合构件中获得的比断裂模量和剪切强度的结果分别与从浇筑构件中获得的结果相当，表明混合配置可能为结构混凝土构件的建造提供可行的替代方案。最后，将研究中使用的不同配置的断裂模量和剪切应力值与 ACI 318-19 规范中的设计表达式进行了比较。研究发现，本研究中使用的混合元件和铸造元件满足最低要求，更大规模的进一步研究可以证实它们在结构应用中的用途。