Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “RESIDUAL STRESS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

IACMI Project 4.2: Thermoplastic Composite Development for Wind Turbine Blades

(Section 5.1) Composites made from Arkema’s Elium® thermoplastic resin and Johns Manville fiberglass were researched during this project for applications in wind blade manufacturing. A techno-economic model was developed to model this wind blade manufacturing process using these materials in place of traditional composites made with thermoset resin. This model was based on manufacturing a 61.5-meter wind blade, which showed a 4.7% reduction in wind blade cost as compared traditional thermoset materials. These cost savings were not from the thermoplastic material costing less than traditional thermoset materials, but rather from decreased capital costs, faster cycle times and reduced energy requirements and labor costs. (Section 5.2) An infusion and curing model was developed for thermoplastic composite wind blades using PAM-RTM. The primary goal was to demonstrate the infusion simulation for the Elium® resin system on a 13-meter wind blade. Additionally, the exotherm temperature was predicted and compared to measurements, which showed model results within 10% of actual measurements. (Section 5.3) Composite laminate panels and composite sandwich panels with a balsa core were produced; specimens were cut and characterized. Similar composite specimens were made with Elium® thermoplastic resin and Hexion thermoset epoxy (RIMR135/RIMH1366) to enable comparisons between these resin systems. The static test methods included: tensile, compression, in-plane shear, interlaminar shear, flexural, sandwich core shear flexure, and single cantilever beam tests for sandwich beams. Fatigue testing at room temperature was completed to composite laminate panels at a stress ratio of R=0.1 and R=10. In addition, fatigue testing to laminate panels was completed at -30°C, and at room temperature after conditioning specimens at 70°C and 90% relative humidity. Overall, mechanical test results from Elium® composites are similar to epoxy composites. (Section 5.4) Elium composite panels were produced with intentional defects such as voids and nonwetting of fibers to begin to understand performance sensitivity to defects. A thermal digital image correlation (TDIC) method provides high spatial resolution strain field at elevated temperatures and can be used to identify defective regions within composite panels. Flexural modulus differences of 21% were seen between defect and non-defect panels. Other Elium® composite panels were forced to be defective by boiling the resin after infusion, which created voids throughout the composite laminate. X-ray computed tomography scanning was used to view the internal structure of the defect panels. Defect panels had a significant reduction in fatigue life as compared to baseline panels produced without intentional defects. (Section 5.5) Lap shear specimens were fabricated to compare the lap shear strength of an off-the-shelf adhesive (Plexus MA590) and two new adhesives developed by Arkema (Bostik SAF30 90 and Bostik SAF30 120). ISO standard 4587:2003 was used to standardize the testing method and sample fabrication. Lap shear specimens were made at 1mm, 3mm, and 10mm thicknesses. The Bostik adhesive lap shear test results were similar to Plexus for all thicknesses. (Section 5.6) Fiber-reinforced polymer (FRP) composites are typically used in high-performance applications (e.g., aerospace), and their expansion into high-volume industries (e.g. consumer automotive and wind turbine blade manufacturer or similar) is hindered by their cost and a lack of efficient manufacturing techniques. Monitoring the curing process of these composites during manufacturing can improve the efficiency of the process, and therefore reduce the manufacturing cost. Cure monitoring techniques were developed that use probabilistic estimation methods and surface temperature measurements made using infrared cameras. These techniques enable real-time monitoring of the infusion process to locate manufacturing flaws, and they can, potentially, estimate residual stresses in the part. Their commercialization will help facilitate expansion of FRP composites in high-volume industries. (Section 5.7) A 13-meter composite wind blade was produced with Elium® resin and Johns Manville fiberglass; this blade was made with VARTM processing similar to how megawatt-scale wind blades are currently manufactured, but no post-mold heating was used for this thermoplastic composite blade. The wind blade underwent full-scale validation for static loading (4-different load orientations) and flapwise fatigue loading to simulate 20-years of operational loads. The thermoplastic composite wind blade withstood the loading without any noted issues and performed similar to results from a previous full-scale validation to an equivalent epoxy composite wind blade produced with the same blade molds. (Section 5.8) A study was conducted to determine the feasibility of recycling composite wind turbine blade components fabricated with glass fiber reinforced Elium® thermoplastic resin. Dissolution, which is a process unique to thermoplastic matrices, allows recovery of both the polymer matrix and full-length glass fibers, while maintaining their stiffness and strength throughout the recovery process. The economics of recycling is favorable if 50% of the glass fiber is recovered and resold for a process of $\$$ 0.28/kg, and 90% of the resin is recovered and resold at a price of $\$$ 2.50/kg.(Section 10) Recommendations are outlined for commercializing thermoplastic resin for composite wind blade production, in addition to recommended areas for future research.

17 WIND ENERGY↗
DOE OSTI2019

Update on Investigations of Viability of Cold Spray and FSW as a Spent Nuclear Fuel Dry Storage Canister Mitigation Tool

The purpose of this work is to investigate the use of cold spray and friction stir welding or processing (FSW/P) for repair and mitigation of chloride-induced stress corrosion cracking (CISCC) in dry cask storage system (DCSS) canisters to ensure integrity far beyond their original license period. This report provides a viability analysis of cold spray and friction stir welding for repair and fabrication of DCSS canisters. This report presents experimental work and a research strategy to optimize and evaluate cold spray and FSW/P for CISCC resistance. The literature reports that the following three conditions must exist for CISCC to occur: tensile stress, corrosive environment, and susceptible material. These conditions must be understood and accounted for while evaluating CISCC susceptibility. Furthermore, non-obvious factors, such as surface conditions and geometric confinement, can dramatically increase the intensity of one or more of the three listed conditions for CISCC. Arc welding should be considered for either temporary or permanent repair when combined with a mitigation technology. It is known that alloys used in the existing inventory of spent nuclear fuel storage canisters become sensitized in areas around fusion welds. Technologies, such as cold spray or FSW, can mitigate the sensitization caused by fusion welds. FSW/P and cold spray, potential alternatives for fabrication and repair, are solid-phase processes. No melting occurs and the energy input can be controlled such that no harm is done to the base metal during these processes. FSW/P should be considered for use in new fabrication of canisters and repair of existing canisters. Low heat input and grain refinement result in material with improved mechanical properties and comparable generalized corrosion performance relative to base metal. FSW/P offers the potential of through-thickness CISCC resistance. Cold spray should be considered for production, mitigation, and repair of canisters. Cold spray has demonstrated the ability to deposit stainless steel, Inconel alloys, and other alloys on stainless steel 304L such that galvanic potential is matched and resistance to pitting is improved. The technical basis for cold spray mitigation and repair within the overpack using remote robotic equipment is established. A non-obvious application to the research community is the sealing of crevices. All reported instances of CISCC in the fielded nuclear applications were associated with crevice corrosion. This can be avoided by cold spraying to seal crevices. The bulk of the work planned for FY 2020 will be generating coupons for CISCC testing by collaborative projects at Pacific Northwest National Laboratory and Sandia National Laboratories. First an exploratory study will be executed that will include screening studies and process optimization. This task will identify the effect of process parameters on microstructure and CISCC resistance. Optimized parameters will be used to produce a smaller number of coupons for full testing and evaluation. Test methods for evaluating CISCC resistance must meet the following criteria: (1) normalized surface geometry and exposed process microstructure, (2) account for residual stresses, (3) be in a controlled and appropriate test environment, and (4) be numerically quantifiable and repeatable. Failure to meet these criteria could lead to results that cannot be used for comparative analysis of processes and materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Silicon Oxide‐Rich Diamond‐Like Carbon: A Conformal, Ultrasmooth Thin Film Material with High Thermo‐Oxidative Stability

Abstract Silicon oxide‐containing diamond‐like carbon (a‐C:H:Si:O) films are a promising class of protective coatings for environmentally‐demanding applications owing to their lower residual stresses and superior thermal stability and oxidation resistance relative to undoped diamond‐like carbon. However, existing versions of a‐C:H:Si:O deposited by traditional methods such as plasma‐enhanced chemical vapor deposition (PECVD) undergo substantial degradation and oxidation at temperatures above 250 °C. This, together with the difficulty of PECVD in depositing conformal coatings on complex geometries such as high‐aspect‐ratio features, has limited the applicability of a‐C:H:Si:O. Here, the unique capabilities of plasma immersion ion implantation and deposition (PIIID) to grow silicon oxide‐rich diamond‐like carbon materials that are ultrasmooth, continuous, and conformal on high‐aspect‐ratio topographies are explored. The high concentration of silicon and oxygen in PIIID‐grown films (23 ± 5 at.% and 11 ± 4 at.%, respectively) is unrivalled for this class of materials, and drastically increases the resistance to oxidation at high temperatures, compared with PECVD‐grown films. The results open the path for using a‐C:H:Si:O in applications involving exposure of materials to extreme environments.

Mangolini, Filippo↗
DOE OSTI2017

Parameter estimation in a thermoelastic composite problem via adjoint formulation and model reduction

Advances in nondestructive material characterization are providing a wealth of information that could be exploited to gain insight into general aspects of material performance and, in particular, discover relationships between microstructure and thermo-mechanical properties in polycrystalline and other complex composite materials. Here, in order to facilitate the integration of such measurements into existing models, as well as inform new physics-based predictions, we developed a C++/MPI computational framework for sensitivity analysis and parameter estimation. The framework utilizes a micro-mechanical modeling based on fast Fourier transforms, direct and adjoint formulations, and Markov chain Monte Carlo sampling techniques. We illustrate the characteristics of this framework and demonstrate its utility by computing the residual stresses arising from thermal expansion of an elastic composite and using data from simulated experiments. Lastly, we show that the availability of nondestructive 3-D measurements is crucial to reduce the uncertainty in predictions, emphasizing the importance of an integrated experimental/modeling/data analysis approach for improved material characterization and design.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigating Chain Dynamics in Highly Crosslinked Polymers using Solid–State 1 H NMR Spectroscopy

Solid state 1 H NMR line–shape analysis and (double quantum) DQ 1 H NMR experiments have been used to investigate the segmental and polymer chain dynamics as a function of temperature for a series of thermosetting epoxy resins produced using different diamine curing agents. In these thermosets, chemical crosslinks introduce topological constraints leading to residual stresses during curing. Materials containing a unique ferrocene–based diamine (FcDA) curing agent were evaluated to address the role of the ferrocene fluxional process on the atomic–level polymer dynamics. Here, at temperatures above the glass transition temperature ( T g), the DQ 1 H NMR experiments provided a measure of the relative effective crosslink and entanglement densities for these materials and revealed significant polymer chain dynamic heterogeneity in the FcDA–cured thermosets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Thermal Performance of Perovskite-Based Photovoltaics for Operation in Low Earth Orbit

Perovskite-based photovoltaics are attractive for applications in space. The space environment is harsh with ionizing radiation, atomic oxygen, UV radiation, extreme temperatures, and thermal cycling. Herein, the thermal performance of perovskite active layer and perovskite photovoltaic devices in low earth orbit is analyzed. A 1 μm silicon oxide layer coupled with 500 nm zirconia thin film aid in cell thermal management is determined. The residual stresses between various layers in a device are modeled and it is proved that thermally induced mechanical failure of the perovskite (time > 460 years) is unlikely during operating lifetime of any mission. In conclusion, target power conversion efficiencies are also shared to manage maximum operating temperature of a perovskite-based device.

14 SOLAR ENERGY↗
DOE OSTI2014

Implementation of a thermomechanical model for the simulation of selective laser melting

Selective laser melting (SLM) is an additive manufacturing process in which multiple, successive layers of metal powders are heated via laser in order to build a part. Modeling of SLM requires consideration of both heat transfer and solid mechanics. The present work describes continuum modeling of SLM as envisioned for eventual support of part-scale modeling of this fabrication process to determine end-state information such as residual stresses and distortion. The determination of the evolving temperatures is dependent on the material, the state of the material (powder or solid), the specified heating, and the configuration. Similarly, the current configuration is dependent on the temperatures, the powder-solid state, and the constitutive models. A multi-physics numerical formulation is required to solve such problems. This article describes the problem formulation, numerical method, and constitutive parameters necessary to solve such a problem. Additionally, various verification and example problems are simulated in the parallel, multi-physics finite element code Diablo, and the results presented herein.

42 ENGINEERING↗
DOE OSTI2016

Processing of crack-free high density polycrystalline LiTaO3 ceramics

Our work achieved high density (99.9%) polycrystalline LiTaO 3 . The keys to the high density without cracking were the use of LiF-assisted densification to maintain fine grain size as well as the presence of secondary lithium aluminate phases as grain growth inhibitors. The average grain size of the hot pressed polycrystalline LiTaO 3 is less than 5 μm, limiting residual stresses caused by the anisotropic thermal expansion. Dilatometry results clearly indicate liquid phase sintering via the added LiF sintering aid. Efficient liquid phase sintering allows densification during low temperature hot pressing. Electron microscopy confirmed the high-density microstructure. Furthermore, Rietveld analysis of neutron diffraction data revealed the presence of LiAlO 2 and LiAl 5 O 8 minority phases and negligible substitutional defect incorporation in LiTaO 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2018

Analysis of Nonclassical Fracture Problems for Prestressed Bodies with Interacting Cracks

We consider two types of nonclassical fracture mechanisms, namely, the fracture of cracked bodies with initial (residual) stresses acting along the crack planes and the fracture of solids under compression along parallel cracks. To investigate nonaxisymmetric and axisymmetric problems for infinite solids containing two parallel coaxial cracks or a periodic set of coaxial parallel cracks, we use a combined analytic-numerical method within the framework of the three-dimensional linearized mechanics of solids. The analysis involves the representation of stresses and displacements in the linearized theory via harmonic potential functions. With the use of the integral Fourier–Hankel transformations, the problems are reduced to the solution of Fredholm integral equations of the second kind. This approach allows us to investigate problems in a unified general form for compressible and noncompressible homogeneous isotropic or transversely isotropic elastic bodies with an arbitrary structure of the elastic potential, and the material specification of the model is carried out only in the stage of numerical analysis of the resolving equations obtained in the general form. The effects of initial stresses on the stress intensity factors are analyzed for highly elastic materials and layered composites (modeled as transversely isotropic elastic bodies). The “resonance-like” effects are revealed when compressive initial stresses reach the values corresponding to the local loss of stability of the material in the vicinity of cracks, which, according to the indicated combined method, allows one to determine the critical (limiting) load parameters under the conditions of compression of the body along the cracks. The conclusions concerning the dependences of the stress intensity factors and critical (limiting) parameters of compression on the geometric parameters of the problems are formulated as well as concerning the dependences on physical and mechanical characteristics of the materials.

42 ENGINEERING↗
DOE OSTI2019

The Effect of HVOF Bond Coating with APS Flash Coating on TBC Performance

To study the benefit of ~ 50-µm-thick air-plasma-sprayed (APS) ‘flash’ bond coatings, NiCoCrAlYHfSi high-velocity oxygen fuel (HVOF) bond coatings were deposited on alloy 247 disk substrates with APS yttria-stabilized zirconia topcoatings. Using 1-h cycles at 1100 °C in air with 10% H 2 O and HVOF-only bond coatings as a baseline, APS flash coatings extended the average coating lifetime by > 10% using NiCoCrAlYHfSi and > 70% using NiCoCrAlY powder. Coatings were characterized after 0, 100 and 300 cycles and after failure. Residual stress in the thermally grown alumina scale was mapped every 100 cycles using photo-stimulated luminescence piezospectroscopy. The flash coating created an interlocked metal–alumina layer that appeared to inhibit critical crack formation, and the underlying HVOF layer prevented further internal oxidation and appeared to supply the APS flash coating with Al. Furthermore, the addition of Hf and Y to the flash coating increased internal oxidation and accelerated Al consumption, thereby reducing the benefit of the flash coating.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The Effect of APS-HVOF Bond Coating Thickness Ratio on TBC Furnace Cycle Lifetime

In this work, combinations of NiCoCrAlY APS and high-velocity oxygen fuel (HVOF) bond coatings were deposited on alloy 247 disk substrates with APS yttria-stabilized zirconia (YSZ) top coatings to assess the benefit of air plasma sprayed (APS) ‘flash’ bond coatings. Using 1-h cycles at 1100 °C in air with 10% H 2 O and HVOF-only and APS-only bond coatings as a baseline, it was found that APS flash coatings extended the average coating lifetime by 16% to 35% with the thicker flash coating performing best. Principal component analysis and energy dispersive spectroscopy (EDS) compositional mapping on coatings characterized after 0, 100, 300 and 500 cycles and after failure showed that the Al in the bond coatings was depleted due to both oxidation and back diffusion into the substrate. The APS-only bond coating had significant oxidation throughout the bond coating and was so depleted in Al, that Al diffused from the substrate to the coating. Residual stress maps of the thermally-grown alumina scale were obtained every 100 cycles using photo-stimulated luminescence piezospectroscopy (PLPS) revealing that the Thick Flash coating had the slowest rate of damage accumulation in the oxide scale.

alumina scale↗
DOE OSTI2025

Time-Dependent 600 °C Post-Weld Heat Treatment Response of Laser-Wire-Directed Energy Deposited Austenitic Stainless Steel Claddings on Carbon Steel

Austenitic stainless steel overlay claddings are often used to protect nuclear reactor pressure vessels from corrosion. Arc welding processes are traditionally employed, which require a high heat input to bond the dissimilar metals, creating a large heat-affected zone and high residual stress that demands a lengthy stress-relieving post-weld heat treatment, up to 48 hours. High energy beam (e.g., laser, electron beam) directed energy deposition-based overlay cladding processes show promise for fabricating claddings with superior performance compared to arc welded ones because of their localized heat input; however, their necessity and time of post-weld heat treatment are currently unclear. In this research, we investigate the time dependence of a 600 C stress-relieving post-weld heat treatment of austenitic stainless steel clad on low carbon steel by laser-wire-directed energy deposition, comparing the microstructure and mechanical properties of the as-fabricated condition to 2-, 10-, and 48-hour heat treatment times. Diffusion simulations and microscopy show a gradual carburization of the stainless steel cladding and decarburization of the heat-affected zone/base metal. Nanoindentation testing shows up to a 1.8–2.69 embrittlement in the cladding and a 0.33 to 0.69 softening in the heat-affected zone after the 48-hour post-weld heat treatment. Tensile testing of the cladding composites reveals that increasing post-weld heat treatment time raises clad cracking susceptibility due to intergranular carbide formation and shows that laser-wire-directed energy deposition claddings may not require post-weld heat treatment.

Coating↗
DOE OSTI2025

Multimodal Defect Imaging of Pure Tungsten Components Fabricated via Electron Beam Powder Bed Fusion

The utilization of additive manufacturing (AM) techniques for refractory materials in high-temperature environments has significantly expanded because of the ability to fabricate geometrically complex components. Electron beam powder bed fusion (EB-PBF), which provides lower residual stress, a cleaner vacuum environment, and better efficiency for high melting point, is one of the best-suited AM methods to produce advanced refractory components. However, the property variation attributed to the heterogeneous microstructure and process-induced defects has hindered the widespread adoption of EB-PBF-produced material like tungsten. While numerous in-situ monitoring and defect detection methods have been demonstrated for EB-PBF, a workflow that compares and evaluates process-induced abnormalities from different imaging perspectives is still limited. This study examines a feature-embedded tungsten component manufactured via the EB-PBF process to demonstrate the defect detection capabilities of a multimodal defect imaging workflow. The predefined and process-induced defects are evaluated by harnessing various imaging techniques, including in-situ electron imaging, layerwise near-infrared (NIR) imaging, post-build high-energy x-ray computed tomography (CT), and conventional destructive metallography. The results highlight the strengths and limitations of distinctive defect imaging techniques concerning specific defect types, sizes, and conditions. It was found that electron imaging can provide more abnormal detection capabilities while maintaining a higher measuring accuracy, against the conventional metallography in this case study, compared with NIR and CT imaging techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructure and Temperature Dependent Indentation Response of Additively Manufactured Precipitation-Strengthened Al 0.3 Ti 0.2 Co 0.7 CrFeNi 1.7 High Entropy Alloy

The temperature-dependent [from room temperature (RT) to 500°C] nanoindentation behavior of a precipitation-strengthened Al 0.3 Ti 0.2 Co 0.7 CrFeNi 1.7 high-entropy alloy (HEA) processed via two different additive manufacturing (AM) techniques was investigated in the as-deposited and annealed conditions. The hierarchically heterogeneous microstructures were achieved via simple one-step annealing treatments, exploiting the residual stresses in the AM-processed HEA to partially recrystallize the microstructure, performed remarkably better than the nearly homogeneous microstructures in the as-deposited state. Further, the one-step annealed conditions revealed < 6.6% reduction in hardness values at 500°C compared to RT, while the as-deposited conditions showed a > 18% reduction in the hardness. The one-step annealed conditions also exhibited significantly higher hardness than the as-deposited conditions owing to their L1 2 -strengthened FCC microstructures. Furthermore, serrated yielding or the Portevin-Le Chatlier effect indicative of microstructural instability was observed during nanoindentation deformation (at 500°C) for the as-deposited conditions but not for the one-step annealed conditions. This, therefore, signifies the robustness of the hierarchically heterogeneous microstructures at elevated temperatures presenting a strong avenue for tuning the HEAs for future nuclear reactor applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Part distortion monitoring in additive manufacturing using machining

In additive manufacturing, accumulation of residual stresses can result in severe part distortion from the desired preform shape. Current methods for in-situ part distortion monitoring in additive manufacturing typically require expensive sensors, or capital equipment, and require time-consuming post-processing to understand the shape deviation. This paper presents an in-situ method, in the context of hybrid manufacturing, for part distortion detection using machining of additively manufactured parts. As a surrogate, three test artifacts were used to represent different distorted geometries. The tool axis positions from the machine tool controller and the cutting power were monitored during a facing operation. Cutting power data was used to detect the tool entry and exit in the workpiece using a novel approach with power standard deviation metric. The workpiece geometry and distorted configuration was subsequently predicted for positional and rotational deviations to within 2 mm accuracy using synchronized tool position data with cutting power. The proposed method can be used in a hybrid (additive and subtractive) machine tool to periodically check part distortion in the additive build. The method is applicable for any additive process and is low-cost and computationally inexpensive.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Localized material compression to correct distortion in wire arc additive manufacturing

Wire Arc Additive Manufacturing (WAAM) is an advanced manufacturing technology which utilizes welding systems to generate three dimensional geometries in a layer-by-layer fashion. Distortion or warping of a print substrate and WAAM components due to thermally induced residual stresses is an ongoing challenge limiting the widespread adoption of WAAM technologies for producing components. In this manuscript, a novel approach is described to address thermal distortion in deposited components by applying lateral compressions along the length of the deposited material. To demonstrate this method, a series of single-track walls were printed and compressed at evenly spaced intervals using a modified hydraulic cutter tool. The jaws of the tool were modified to compress material rather than to shear it. A mathematical model was developed to relate the curvature of the deposited material to the volume of compression required to eliminate this distortion. Validation of this model was performed using 3D scan data to compare the change in wall curvature induced by compression to the volume of the applied compressions. Substrate deflection was also compared against a control wall, and implementation of wall compression reduced maximum deflections by 93% across a series of four depositions and subsequent compressions. Wall cross sections were also analyzed to determine the impact of compression on material hardness and grain structure. The results demonstrate that successively placed lateral compressions can effectively control and potentially eliminate bending distortion in printed parts. This methodology can be further developed to form a robust model for correction of thermally-induced distortion in WAAM components.

Additive manufacturing↗
DOE OSTI2018

A thermal-mechanical finite element workflow for directed energy deposition additive manufacturing process modeling

This work proposes a finite element (FE) analysis workflow to simulate directed energy deposition (DED) additive manufacturing at a macroscopic length scale (i.e. part length scale) and to predict thermal conditions during manufacturing, as well as distortions, strength and residual stresses at the completion of manufacturing. The proposed analysis method incorporates a multi-step FE workflow to elucidate the thermal and mechanical responses in laser engineered net shaping (LENS) manufacturing. For each time step, a thermal element activation scheme captures the material deposition process. Then, activated elements and their associated geometry are analyzed first thermally for heat flow due to radiation, convection, and conduction, and then mechanically for the resulting stresses, displacements, and material property evolution. Finally, simulations agree with experimentally measured in situ thermal measurements for simple cylindrical build geometries, as well as general trends of local hardness distribution and plastic strain accumulation (represented by relative distribution of geometrically necessary dislocations).

42 ENGINEERING↗
DOE OSTI2018

Laser peening: A tool for additive manufacturing post-processing

Additive manufacturing (AM) is rapidly moving from research to commercial applications due to its ability to produce geometric features difficult or impossible to generate by conventional machining. Fielded components need to endure fatigue loadings over long operational lifetimes. This work evaluates the ability of shot and laser peening to enhance the fatigue lifetime and strength of AM parts. As previously shown, peening processes induce beneficial microstructure and residual stress enhancement; this work takes a step to demonstrate the fatigue enhancement of peening including for the case of geometric stress risers as expected for fielded AM components. We present AM sample fatigue results with and without a stress riser using untreated baseline samples and shot and laser peening surface treatments. Laser peening is clearly shown to provide superior fatigue life and strength. We also investigated the ability of analysis to select laser peening parameters and coverage that can shape and/or correctively reshape AM components to a high degree of precision. We demonstrated this potential by shaping and shape correction using our finite element based predictive modeling and highly controlled laser peening.

42 ENGINEERING↗