Papers by Keyword: Bending Fatigue

Abstract: This study was initiated to investigate the material characteristics of binder jet (BJ) manufactured austenitic stainless steel 316L, focusing specifically on the less studied bronze infiltrated version of this material. While BJ technology offers a compelling alternative to the current market leader laser powder bed fusion, all additive manufacturing methods are susceptible to porosity, which adversely affects the fatigue properties of parts, resulting in inferior fatigue life compared to traditionally manufactured counterparts. In this study, we explore the novel application of severe shot peening (SSP) as a post-processing method to enhance fatigue life. Through comprehensive microstructural analysis utilizing EBSD, mechanical properties testing via tensile testing, and fatigue life analysis using flexural bending fatigue testing, we demonstrate that SSP treatment induces surface modification, leading to increased material strength albeit with a trade-off in ductility. Moreover, our findings reveal a significant improvement in the fatigue life of the material. Utilizing SSP, we observed that the fatigue limit of the material more than doubled, surpassing the performance of the sheet metal counterpart of the same material. These results underscore the potential of SSP as an attractive method for property enhancement in additive manufacturing.

Abstract: This study investigates the mechanical properties and microstructure of 316L stainless steel fabricated using laser powder bed fusion (PBF-LB) additive manufacturing with different layer thick nesses and orientations. Impact toughness is evaluated under various conditions as well as bending fatigue performance to understand the influence of layer thickness and surface quality on fatigue lim its. Microstructural analysis using scanning electron microscopy (SEM) provides insights into grain structure. Key findings include the superior impact toughness of the vertical orientation, particularly notable in specimens with a layer thickness of 40 µm. Bending fatigue tests revealed distinctive behav ior influenced by layer thickness and surface quality, with the 80 µm thickness and vertical orientation demonstrating lower fatigue limits. These insights contribute to optimizing manufacturing processes and enhancing material suitability for diverse applications.

Abstract: Additive manufacturing (AM) techniques, particularly Laser Powder Bed Fusion (PBF-LB), have revolutionized the production of complex components, offering unparalleled design freedom and material customization. This paper delves into the mechanical intricacies of AlSi10Mg manufactured via PBF-LB, with a specific focus on its mechanical properties and fatigue behavior under different loading conditions when the material has not been heat treated. The study investigates the influence of printing orientation on the mechanical characteristics of AlSi10Mg components. It is revealed that build orientation plays a crucial role in determining the material’s mechanical response, with distinct trends observed in different orientations. Furthermore, the fatigue performance of AlSi10Mg under flexural bending and axial loading conditions are studied. Results indicate a significant enhancement in fatigue resistance when components are printed in optimal orientations, underscoring the importance of orientation control in additive manufacturing processes. Overall, this study contributes to a comprehensive understanding of the mechanical behavior of AlSi10Mg produced via PBF-LB, offering insights for optimizing component design and manufacturing processes in various industries.

Abstract: Additive manufacturing, specifically Laser Powder Bed Fusion (PBF-LB), has gained prominence for its capability to produce complex near-net-shaped components. While PBF-LB offers advantages such as lightweight construction and cost-effectiveness, post-processing remains crucial to meet specific design requirements. This study investigates the post-processing technique of severe shot peening (SSP) on PBF-LB-manufactured 316L stainless steel, a material widely used for its favorable mechanical properties and corrosion resistance. The research focuses on the enhancement of bending fatigue properties through SSP treatment, examining the influence of material thickness on fatigue behavior. Comparative analysis reveals the effectiveness of SSP in significantly improving fatigue strength irrespective of variations in material thickness. Mechanical properties are explored for different thicknesses subjected to SSP treatment. Electron Backscatter Diffraction (EBSD) is employed to scrutinize the surface properties of the samples, providing knowledge on the microstructural changes induced by SSP. The study contributes to the understanding of the role of material thickness in the context of SSP treatment, offering a comprehensive exploration of the mechanical and fatigue characteristics of PBF-LB-manufactured 316L stainless steel.

Abstract: Titanium alloys are highly valued in various industries due to their exceptional qualities. This study examines how the build orientation affects the mechanical and fatigue properties of Laser Powder Bed Fusion (PBF-LB) produced Ti6Al4V, without heat treatment. The research shows mechanical properties vary based on build orientation with vertically oriented specimens exhibiting the highest yield and tensile strengths, while vertical orientation excels in ductility, measured through elongation at break. Impact toughness sees variations with horizontal orientation performing the best. However, build orientation has minimal influence on flexural bending fatigue performance. Both diagonal and vertical orientations show similar fatigue limits at around 40 MPa. Dry electropolishing proves to be an effective technique, significantly enhancing fatigue performance with limits stabilizing at about 150 MPa. This study underscores the importance of considering build orientation in PBF-LB manufacturing for specific mechanical and impact properties and the potential of dry electropolishing in improving the fatigue performance of Ti6Al4V components. These findings offer valuable insights for the additive manufacturing industry, aiding in the optimization of Ti6Al4V component production.

Abstract: Transient liquid phase (TLP) bonds using Cu-Sn system have been suggested as high strength and temperature resistant joints for power electronics applications. While the physical and mechanical properties of these joints has been investigated to some extent, studies on fatigue properties and long term reliability of TLP joints are scarce. In this work TLP bonding was performed to produce thin Cu-Sn intermetallic joints by using Cu and 97Sn3Cu solder alloy as interlayer. Different processing conditions resulted in three types of thin joints consisting of three phases (Cu₃Sn/Cu₆Sn₅/solder remnants), two phases (Cu₃Sn/Cu₆Sn₅) and a single phase (Cu₃Sn) with an overall thickness of ≤ 20 μm. The shear strength of the TLP joint containing one or two high melting point IMC layers showed a significant temperature resistance up to 200°C. Fatigue studies of TLP joints were conducted by using a 3-point-cyclic bending test system operating at 20 kHz. The highest fatigue resistance was obtained for the single-phase Cu₃Sn joints with superior shear and flexural resistance. The two phase joints (Cu₃Sn/Cu₆Sn₅) showed a slightly lower lifetime than the three phase system containing IMCs and residual solder. Fracture surfaces analysis in correlation with static and cyclic mechanical properties, provided insight into the failure mechanism of the Cu-Sn TLP joints.

Abstract: The paper presents the assembling flux of thermocouple-instrumented nuclear fuel element for research reactor, from the point of view of the welding / brazing engineer, considering nuclear quality and safety requirements: fuel element structural reliability (no radioactive leaks through joints) and temperature signal reliability (thermocouple sheath integrity), this signal being an essential parameter for reactor normal operation and emergency shut-down. The paper is a real case study for an experimental instrumented element recently developed at INR-Pitesti describing technology choices as balance between fabrication complexity and risk of failure in joining processes, especially in later stages when added value increases. All joints (welded or brazed) fall into microjoining category, and it is shown how some special provisions may influence reliability. Focus is put on brazing thin-walled Inconel sheathed thermocouples, where erosion and local loss of ductility are known issues, leading to sheath rupture. Choosing as filler the less aggressive BNi-9 helped too little. A simple but efficient technique has been developed to address this matter adequate to narrow spaces inside a nuclear fuel element, where no room is available for solutions described in literature e.g. distal preplacing of filler. The solution prevents sheath from having prolonged contact with large volume of molten filler by using locally a miniature barrier (thin stainless-steel coil or sleeve) which only allows capillary wetting, being also a perfect real-time visual indicator of brazing progress and completion. As proved in the present paper, this method along with using filler formulation with lower Carbon content (without organic binder) enhances significantly, 8 times at least, resistance to bending fatigue. A particular vacuum brazing chamber design is employed: narrow quartz tube with external induction coil and top fitting letting outside the long thermocouples attached, reducing much the chamber volume and degassing. Careful impedance match is therefore required to overcome induction power loss due to the larger coil-to-workpiece gap. Additional joining problems are discussed e.g. inherent differential expansion of long parts during induction heating which afterwards may put tension upon braze during solidification and determine delayed cracking, this being avoided through wise order of operations. Another concern is the final precision weld between instrumentation segment having attached the hard-to-handle long thermocouples bunch and nuclear segment with the heavy Uranium pellets. The result of this research is successful assembling of first Romanian prototype with joints exhibiting He leak rate bellow 1E-09 std.cc/sec and overall reliability proved during reactor irradiation testing.

Abstract: The paper discusses the computational and experimental approach for determination of the PM gears service life concerning bending fatigue in a gear tooth root. A proposed computational model is based on the stress-life approach where the stress field in a gear tooth root is determined numerically using FEM. The experimental procedure was done on a custom made back-to-back gear testing rig. The comparison between computational and experimental results has shown that the proposed computational approach is appropriate calculation method for service life estimation of sintered gears regarding tooth root strength. Namely, it was shown that in the case of proper heat treatment of tested gears, the tooth breakage occurred inside the interval with 95 % probability of failure, which has been determined using proposed computational model.

Abstract: The paper deals with an investigation of surface laser hardening characteristics on contact and bending fatigue resistance of a 42CrMo4 steel, being often used for manufacture of gear wheels. The aim of the experimental programme was to simulate the complex service loading of fairly large gears by two separate investigations, namely contact fatigue performed on a special, so called analogon machine and bending fatigue performed on high cycle fatigue resonance machines using three-point-bend (3PB) fairly large specimens. It was shown that after optimising the methodology and parameters of the laser hardening technology, contact fatigue resistance is very good, comparable with very expensive and time consuming thermochemical high-depth surface treatments. Bending endurance limit can be increased. The role of residual stresses resulting from the laser treatment was shown as decisive.

Abstract: Gimbaling the engine nozzle within a specified angle through hydraulic actuator modules is commonly used to control the trajectory path of satellite launch vehicles. During one of the hot test of a liquid engine stage, a drop in system pressure in actuator module was noticed due to cracking of case drain plumbing inside the ferrule. The tensile and fatigue (axial and bending) test of the tube material was carried out to understand the cause of failure, simulating the actual service conditions such as strength and bending moment in assembled tube. Findings of the metallurgical investigation along with the fatigue test results were presented in this paper.