Failure Analysis of Additive Manufactured Fiber-Reinforced Thermoplastics

Journal of Failure Analysis and Prevention - In the present work, a comprehensive study is undertaken to analyze the mechanical strength and failure of different polymers reinforced with adaptable...     

Characterization of Microstructure in Additively Manufactured 316L using Automated Serial Sectioning

A review is presented of recent advancements in characterization and automation and how this has led to a new generation of automated serial-sectioning facilities, which has allowed for the analysis of larger 3D datasets with thousands of objects of interest at high resolution. A case study is presented in which the Robotic Serial Sectioning System for 3D (RS^3D) is used to analyze the correlation of the initialization of new grain orientations and defects within additively manufactured 316L steel. Finally, we provide a brief discussion of new technologies including new microscopy methods, machine learning, and sparse sampling that could potentially reduce the effort and cost of collecting and analyzing 3D microstructural data in the near future.     

Experimental Assessment and Micromechanical Modeling of Additively Manufactured Austenitic Steels under Cyclic Loading

The present work deals with the cyclic deformation behavior of additively manufactured austenitic stainless steel 316L. Since fatigue experiments are complex and time-consuming, it is important to develop accurate numerical models to predict cyclic plastic deformation and extrapolate the limited experimental results into a wider range of conditions, considering also the microstructures obtained by additive manufacturing. Herein, specimens of 316L steel are produced by powder bed fusion of metals with laser beams (PBF-LB/M) with different parameters, and cyclic strain tests are performed to assess their deformation behavior under cyclic loads at room temperature. Additionally, a micromechanical model is set up, based on representative volume elements (RVE) mimicking the microstructure of the experimentally tested material that is characterized by electron backscatter diffraction (EBSD) analysis. With the help of these RVEs, the deformation-dependent internal stresses within the microstructure can be simulated in a realistic manner. The additively manufactured specimens are produced with their loading axis either parallel or perpendicular to the building direction, and the resulting anisotropic behavior under cyclic straining is investigated. Results highlight significant effects of specimen orientation and crystallographic texture and only a minor influence of grain shape on cyclic behavior.     

基于神经网络的电弧增材制造铝合金力学性能预测

目的 预测不同工艺参数下电弧增材制造铝合金的力学性能。方法 通过实验建立了电弧增材制造6061铝合金及Ti C增强6061铝合金力学性能的数据集,并建立了一种以焊接电流、焊接速度、脉冲频率、TiC颗粒含量为输入,以屈服强度和抗拉强度为输出的神经网预测模型,对比了反向传播神经网络(BP)、粒子群算法优化BP神经网络(PSO-BP)、遗传算法优化BP神经网络(GA-BP)3种预测模型的精度。结果 与BP模型和PSO-BP模型相比,GA-BP预测模型具有更好的预测精度。其中,GA-BP模型预测6061铝合金屈服强度最佳结果的相关系数(R)为0.965,决定系数(R²)为0.93,平均绝对误差(Mean Absolute Error,MAE)为2.35,均方根误差(Root Mean Square Error,RMSE)为2.67;预测Ti C增强的6061铝合金抗拉强度最佳结果的R=1,R²高达0.99,MAE为0.46,RMSE为0.49,GA-BP具有良好的预测精度。结论 BP、PSO-BP、GA-BP 3种神经网络模型可以用来预测电弧增材制造...     

Characterization of Failure Mechanisms of Duplex and Graded Thermal Barrier Coatings Exposed to Thermal Shock Test

The beginning of failure of a (ZrO2-7%Y2O3)/(Ni-22%Co-17%Cr-12.5%Al-0.6%Y) duplex andgraded coating systems on lnconel 617 and IN738LC in burner rig tests has been characterized.The test conditions are 40 s heating up to 75O℃ substrate temperature followed by 80 s aircooling. Failure is considered at the appearance of the first bright spot during heating period.Stresses due to thermal expansion mismatch strains on cooling are the probable cause of life-limiting in this conditions of testing.     

Failure of Bolt Threads Exposed to Shear Stress

An agricultural grain cart rolled over during harvest when a bolt in the hitch assembly failed. The bolt failed due to high shear stress in a thread root. The bolt would not have failed under the same conditions if the threads were not present in the shear zone (different bolt with a longer shank region). The cart rolled over due to bolt failure as a result of high shear stress.     

超音速激光沉积增材制造CNTs/Cu复合材料微观结构及力学性能研究

目的 研究超音速激光沉积增材制造CNTs/Cu复合材料的微观结构及力学性能。方法 对CNTs进行表面镀铜处理,提高它与Cu黏接相之间的润湿性,增强CNTs/Cu之间的界面结合,利用超音速激光沉积技术(Supersonic Laser Deposition,SLD)增材制备不同CNTs含量的CNTs/Cu复合材料,对比研究了CNTs含量和退火温度对CNTs/Cu复合材料微观结构及力学性能的影响规律,并采用能谱仪对拉伸断口微区进行元素分析测定。结果 SLD制备的CNTs/Cu复合材料具有优异的塑性变形能力,而强度较高的CNTs通过嵌入铜粉颗粒之间的缝隙提升了沉积质量。对复合材料微观组织进行表征发现组织无明显孔隙、致密性良好,且无烧蚀现象。CNTs的加入有效提高了CNTs/Cu复合材料的抗拉性能,并且随着CNTs含量的上升,CNTs/Cu复合材料的极限抗拉强度(Ultimate Tensile Strength,UTS)稳步上升;当CNTs质量分数为0.3%时,CNTs/Cu复合材料的UTS为36.33 MPa,是CNTs质量分数为0.05%时的1.35倍。随着退火温度的升高,CNTs/Cu复合材料的UTS表现为先增大后减小的趋势,在500 ℃时UTS达到最大值。结论 由于激光加热软化的效果与表面镀铜的包覆作用,CNTs能够均匀地分布在CNTs/Cu复合材料内部,同时明显增强复合材料内部颗粒的界面结合强度,后续的热处理有助于使材料从不稳定的机械结合逐步转换为冶金结合,显著提高复合材料的抗拉性能。     

Analysis of Failure in Automobile Spokes Manufactured Using Medium Carbon Steel Wires

Medium carbon steel wires are used to manufacture spokes for motor vehicles, and the integrity of the spokes is very important from the point of view of safety to the driver of the vehicle. In this paper, analysis of failure of one batch of spokes has been presented. The spokes failed during assembling on to the wheels and also during the field trials. In order to understand the root cause of these failures, metallurgical investigation of these spokes was done. It involved fractography, scanning electron microscopy, EDS analysis, optical microscopy, hardness testing, tensile testing, and chemical analysis. Chemical composition and tensile properties of the material were found to be within the values mentioned in the specification. The cause of failure is concluded to be the wrong microstructure that got developed in the material. The microstructure of the material is coarse lamellar pearlite with ferrite decorated along the grain boundary. Ferrite being softer is preferentially getting deformed in comparison with the rest of the microstructure i.e., pearlite. This preferential deformation in the material is leading to initiation of cracks during the manufacturing of spoke. Additionally, due to higher lamellar spacing in pearlite, ductility of the material has also decreased.