Huang Yuan

Tsinghua University | TH ·  Department of Aeronautics and Astronautics Engineering

Thermomechanical fatigue in distinct crystal orientations of nickel-base single-crystal superalloy was studied. Crack initiation modes and damage mechanisms were characterized on fracture surfaces and longitudinal sections by scanning electron microscope and optical microscope. Creep damage nucleated from casting pores in IP-TMF and propagated unde...

The IN718 superalloy was additively manufactured in three different heat treatment states and three loading directions (0°, 45°, 90°). The anisotropic mechanical properties were investigated based on microstructural analysis and related to the orientation and heat treatments. The differences in mechanical performances are attributed to the precipit...

The effects of the recast layer on the fatigue performance of laser-drilled holes in Ni-based superalloy were experimentally and computationally investigated. It was found that millisecond-laser drilling leads to a recast layer of about 10μm, whereas no recast layer was observed in the picosecond-laser drilled hole. The recast layer was confirmed t...

In the present paper, the crack-tip field of elastoplastic fatigue crack growth without crack closure is computationally confirmed to possess the known HRR solution form, where the stress distributions are controlled by the ΔJ-integral. However, the plasticity-induced crack closure from fatigue crack growth changes the crack characterization dramat...

Lattice metamaterials are widely used in weight-critical applications and gain more design freedoms with the development of additive manufacturing technology, which requires new accurate homogenization methods to model the mechanical behavior of complex microstructures. In the present work, a new homogenization method based on finite element method...

Anisotropic low cycle fatigue (LCF) behavior of nickel-base single crystal superalloy was studied in three distinct crystal orientations. Fractography analysis revealed that activated slip systems under tension were octahedral for the [001]/[011] specimens and cubic slip systems for the [111] specimens, respectively. Based on the critical slip plan...

In the present work, the mechanical properties and fatigue performance of laser melted mismatching nickel-base superalloys were investigated by multiscale experiments and computations. It confirmed that the local strength degradation does not affect the macroscopic stress–strain responses and overall low-cycle fatigue performance due to the stress...

Multi-dimensional finite element modelings of instrumented sharp indentation on materials with cubic symmetry are conducted. A novel reverse analysis algorithm for identifying elastoplastic properties is established for the cubic material, while the anisotropy of the material is determined by indentations on distinct orientations. Influences of ela...

In recent thermal gradient mechanical fatigue (TGMF) investigations, it is verified that the material fatigue lives are significantly affected by the temperature gradients. Determination of temperature gradients of thin-walled structures is always a difficult task. In the present work, tubular specimens were experimentally and computationally inves...

In newly developed hydrogel-based devices, hydrogels are commonly used in load-bearing components subjected to prolonged cyclic deformations. The anti-fatigue capability of hydrogels is crucial for extending the service life of the devices. While recent developments in the synthesis and characterisation of tough hydrogels have facilitated continuou...

The present work is aimed at establishing an engineering design method for fretting fatigue based on experimental and computational investigation of dovetail structures made of nickel‐based superalloy. Severe stress gradients and surface wear damage make fretting fatigue difficult to be assessed based on conventional fatigue life models. With the h...

The present work focuses on heat treatment effects on cyclic plasticity behavior, multiscale strengthening mechanisms and low cycle fatigue performance of laser melting nickel-based superalloys. Microscopic indentation analysis, mesoscopic DIC analysis and macroscopic material testing were conducted to identify multiscale mechanical properties. A D...

The evolution and orientation-dependent behavior of microstructures in dual-phase materials significantly affect the mechanical properties. How to quantify the microstructural effect in a continuum constitutive model, especially considering anisotropic elastic–plastic properties, is still a tough research topic for multiscale mechanics. In the pres...

Deformation-induced martensitic transformation (DIMT) under cyclic loading in metastable austenitic steel AISI 348 was in-situ monitored through the magnetic permeability method with a Feritscope. Stepwise cyclic loading tests under room temperature revealed nonlinear and non-monotonic variations of the magnetic permeability within single loading c...

Temperature gradients are significant in the fatigue life assessment. Thermal loading conditions were suspected to affect temperature gradients and thermal stresses in structures. In the present work, thin-walled plates and tubes were experimentally investigated to quantify the effects of thermal loads on the through-thickness temperature gradients...

The effects of different heat treatments on the microstructure and mechanical properties of the laser melting nickel-based superalloys were systematically investigated. The strength improvement of the heat-treated material was mainly derived from the aging treatment, which converted the γ matrix together with Niobium to the strengthening phases γ′′...

The additively manufactured materials show anisotropic mechanical properties. In the present paper, a constitutive model for a nickel‐based superalloy made by selective laser melting was established to characterize cyclic mechanical behaviors under multiaxial loading conditions. Detailed material tests revealed that the effects from the building or...

In the present work, the microstructures and mechanical properties of additively manufactured IN718 alloy were studied and the dendritic columnar microstructures elongated along the building direction are related to macroscopic mechanical properties. Detailed experiments under both proportional and non-proportional multi-axial loading conditions in...

Continuum descriptions of the microstructure in dual-phase materials are introduced by fabric tensors computed from the mean intercept length (MIL) method. The fabric tensor can be decomposed into the isotropic and deviatoric components to represent the dilatation and orientation preferred properties, respectively. Systematic numerical simulations...

Fretting fatigue is a significant damage mode for turbine engine blade/disk components. In the present work, fretting fatigue crack growth of a nickel-based superalloy was experimentally and computationally investigated. Fretting fatigue experiments of dovetail joints were conducted under loading ratio R=0.1, and the results revealed that the frett...

The existence of multiple cracks affects the crack propagation life assessment of mechanical components. In the present work, numerical algorithms for multiple fatigue crack growth are studied with verification of finite element computations. The investigation confirms that the ratio of the crack center distance to the major crack length is a suita...

The objective of the present work is to characterize the effects of microstructural features, including porosity, precipitates, and to quantify their contributions to the damage evolution in the Inconel 718 alloy built by selective laser melting (SLM). 3D morphology of porous defects in the SLM alloy obtained from X-ray micro-computed tomography be...

In the present paper, the applicability of the ΔJ-integral is computationally investigated under the Masing postulate. It confirms that the path-dependency of ΔJ is more severe than the J-integral under incremental plasticity. ΔJ from loading is up to 20% larger than ΔJ from unloading, which is independent of loading amplitudes but due to non-propo...

Physicochemical and mechanical stimuli can trigger fluid transport and inelastic solid deformations in the fracture process of anisotropic hydrogel composites. The underlying mechanisms for the time-dependent deformation and fracture behaviour of hydrogel composites remain elusive and poorly understood. The present work develops an anisotropic poro...

The thermal barrier coatings (TBCs) are working under complex elevated temperature loading conditions. In the present work, a damage model for the isothermal and cyclic thermal loads was developed to quantify the failure process of the coatings subjected to isothermal and cyclic thermal exposures. Effects of different damage mechanisms, such as the...

In the present work, the fatigue property and crack growth of the laser recasting material were experimentally and computationally investigated. Based on the mechanical properties identified by instrumented indentation, detailed finite element computations were performed within cyclic plasticity. The shielding effect is attributed to strength misma...

The wide application of various laser techniques is motivating research of microstructural evolution in laser manufactured materials and quantification of its mechanical performance. In the present work, the existence and performance of a recasting-affected zone (RAZ) between the melting-solidified material and the base material after single-pulse...

The conventional engineering design of threaded fasteners applies a linear model determining axial force from fastening torque and was found to be applicable only for vanishing inelastic deformations. Applications of the linear formula can result in a significant over-estimate of the axial force. Detailed experiments reveal that plasticity and wear...

Laser manufacturing is widely used in modern industries for its high efficiency and accuracy. In the present work, the microstructures and mechanical properties of the laser-induced recast material on nickel-based superalloy Inconel 718 were systematically investigated. The mechanical property of the recast material was investigated with the help o...

Turbine blades are working under complex thermal gradient mechanical loading conditions. In the present study, a nickel-based single-crystal superalloy CMSX-4 is experimentally and computationally investigated under the thermo-mechanical fatigue (TMF) and thermal gradient mechanical fatigue (TGMF) loading conditions of the in-phase and out-of-phase...

In the present work, the laser recasting superalloy was experimentally and computationally investigated to quantify the effects of laser manufacturing. Local stresses and strains in recasting specimens were tested to establish the fatigue life assessment. A modified plasticity model was used to describe the cyclic plasticity behavior under multiaxi...

Background Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients on the evolution of fatigue damage in nickel-based superalloys.Objective The present study aims to develop a radiation heating system for universal material testing m...

Deformation-induced martensitic transformation (DIMT) has been investigated for many years mainly under monotonic loading conditions. However, the evolution of the DIMT under non-monotonic loading conditions has rarely been studied. The present work experimentally explored the development of DIMT under tension-compression as well as torsion cyclic...

The microstructure evolution and mechanical property degradation are investigated for a nickel-based single crystal superalloy during 1000~1100°C thermal exposure for up to 1000 h. Microstructure analyses are aimed at the coarsening of γ′ precipitates and the formation of rafted structure. The morphology of γ/γ′ phase is described by the coarsening...

Ceramic matrix composites exhibit optimal high temperature property and complex nonlinear behaviors including irreversible deformations and stiffness degradation under different mechanical loading conditions. In the present work, the damage evolution of the material under multi-axial loads considering effects of loading-unloading cyclic was studied...

The thermal barrier coatings (TBC) are working under chemo-thermo-mechanical loading conditions and the failure process is characterized by complex aluminum migration, oxidation reactions and cyclic thermo-mechanical degradation. In the present work, the aluminum migration in EB-PVD TBCs subjected to isothermal and cyclic thermal exposure was studi...

Inherent defects induced in casting process seriously affect mechanical performance and fatigue properties of the material. Micro-structural investigations reveal that the grain size and dendrite microstructure are sensitive to casting processes and change materials property. The fatigue performance of the material decreases with porosity and is ch...

In the present work, a radiation heating system was developed to simulate thermal gradient mechanical fatigue (TGMF) loads in turbines. The specimen is externally heated by radiation and internally cooled by compressed air. Experiments showed that the TGMF life of the nickel-based superalloy is significantly shorter than that of the thermo-mechanic...

It is known that the critical fracture energy value decreases with specimen thickness, whereas the local tensile strength of the material increases with the stress triaxiality. In the present work, the critical fracture energy and the tensile strength depending on stress triaxiality are experimentally investigated and identified with the help of fi...

Ceramic matrix composites display complex mechanical behavior under thermo-mechanical loading conditions. The present work focuses on micro-structural evolution and resultant macroscopic property representation of the composites after cyclic thermal shocks. Micro-structural investigation reveals that variations of the hierarchical porosity in the m...

In the present work the superalloy Inconel 718 manufactured by selective laser melting (SLM) was investigated with focus on micro-structural damage evolution under both monotonic and cyclic loading conditions. Material testing and characterization reveal significantly accelerated damage evolution of the SLM material, in comparing with the forged In...

The oxide/oxide ceramic matrix composites display complex mechanical behavior under thermo-mechanical loading conditions. The present work focuses on micro-structural evolution and resultant macroscopic properties during cyclic thermal shocks. Micro-structural investigation reveals that variations of nano-, micro- and macro-pores in the matrix char...

In the present work a nickel-base superalloy Inconel 718 manufactured by selective laser melting (SLM) was investigated with focus on microstructure, orientation-dependent mechanical property and fatigue performance. Comparative material testing and characterization of the SLM and the forged Inconel 718 revealed significant differences in both micr...

Turbine components generally work under thermomechanical loading conditions with varying temperature and significant temperature gradients. In the present work, a radiation heating system was developed to simulate thermal gradient mechanical fatigue (TGMF) loads in turbines. The specimen is externally heated by radiation and internally cooled by co...

Micro-structure of sintered powder metals is characterized by the high porosity. Experiments confirm that the major mechanical property can be expressed in a power-law function of the porosity. In the present work the interdependence between the porosity and the elastic-plastic mechanical property as well as the damage evolution in sintered metals...

Thermal shock is a typical loading case for high temperature components in turbines. The ceramic matrix composites become attractive for their high temperature behavior. However, their low heat conductivity makes thermal shock damage a typical damage mechanism for the turbine application. In the present paper, microstructural evolutions of the oxid...

Recent investigations revealed significant differences of thermomechanical fatigue from isothermal fatigue. Quantifying effects of thermomechanical loads in fatigue life assessment is still an open issue. In the present work, extensive experiments are performed for a popular nickel-based superalloy under both isothermal and thermomechanical loading...

High temperature components work mainly under thermo-mechanical loading conditions. Recent investigations reveal significant effects of the thermo-mechanical coupling on material behavior. In the present work, extensive experiments are performed for nickel-based superalloy Inconel 718 under both isothermal and thermo-mechanical loading conditions....

During the latest 20 years, the extended finite element method (XFEM) has been gradually used to investigate the crack growth behaviors of different materials in combination with various mechanics models and became the most popular computational tool in analyzing crack problems. This paper classifies three typical theoretical frameworks of the XFEM...

Sintered powder metals play increasingly important role in industry. The most remarkable mechanical characteristics of the sintered material is the high porosity, which characterizes deformations and failure of the material. It is confirmed additionally that manufacturing process affects mechanical behavior and fatigue performance of the material....

Damage tolerance assessment is a keen topic in modern industrial product design. Under certain loading conditions fatigue crack growth is elastoplastic and the Paris’ law becomes not applicable. In the past decades numerous cohesive zone models were proposed and investigated for predicting elastoplastic fatigue crack growth. However, three-dimensio...

A cyclic cohesive zone model is applied to characterize the fatigue crack growth behavior of a IN718 superalloy which is frequently used in aerospace components. In order to improve the limitation of fracture mechanics-based models, besides the predictions of the moderate fatigue crack growth rates at the Paris’ regime and the high fatigue crack gr...

The intergranular crack propagation of the lamellar structure β titanium alloys is investigated by using a modified Gurson-type damage model. The representative microstructure of the lamellar alloy, which consists of the soft α phase layer surrounding the hard grain interiors, is generated based on an advanced Voronoi algorithm. Both the normal fra...

Cohesive zone modeling of fatigue crack growth retardation in aerospace titanium alloy Ti–6Al–4V subjected to a single overload during constant amplitude is presented in this work. The cyclic softening behavior of the bulk material is simulated according to the Ohno–Wang’s cyclic plasticity theory. The fracture process zone is represented by an irr...

Sintered metals are increasingly applied to high performance mechanical parts with limited fatigue life in the automobile industry. The present work focus on quantifying the multiaxial cyclic deformation and fatigue behavior of sintered metals under multiaxial loading conditions. The fatigue experiment includes 40 specimens under 7 strain-controlle...

Computational modeling of three-dimensional crack propagation in very ductile materials is still a challenge in fracture mechanics analysis. In the present work a new stress-triaxiality-dependent cohesive zone model (TCZM) is proposed to describe elastic-plastic fracture process in full three-dimensional specimens. The cohesive parameters are ident...

Carburization is popular in design and fabrication of mechanical parts, such as gears, to improve fatigue performance. However, it is still open how to characterize the mechanical property of carburized steel and to quantify effects of the carburization to fatigue life of carburized parts. In the present paper four types of specimens differently tr...

Surface treatment, e.g. shot peening and deep rolling, is popular in aero engine industry, which induces not only high residual stresses but also severe distortions into the subsurface of mechanical parts. In the present work a meta-stable austenitic steel is experimentally investigated by taking into account of martensitic transformations in plast...

The experimental investigation shows that the damage process in sintered metals starts in almost zero loading and can be divided into three stages: the elastic stage, the secondary stage and finally the tertiary stage. A phenomenological continuum damage model is introduced to predict the inelastic behavior of the sintered material and the damage p...

Most cohesive zone models were used to reproduce fatigue crack growth under small scale yielding and failed to predict elastic–plastic fatigue crack growth. In the present work a new cohesive zone model is introduced to give a uniform description of both fatigue crack growth and elastoplastic rupture. Damage accumulation of the cohesive model conta...

In the present paper, a new nonlocal treatment for micro-mechanical damage modeling is introduced based on the background cell concept. The nonlocal damage variable in the modified GTN damage model is defined as the weighted porosity in analogy to the element-free Galerkin method. The evolution of the damage variable is related to the support domai...

Sintered metals are characterized by the high porosity (⩾ 8%) and voids/micro-cracks in microns. Inelastic behavior of the materials is coupled with micro-crack propagation and coalescence of open voids. In the present work the damage evolution of the sintered iron under multi-axial monotonic loading conditions was investigated experimentally and c...

The cohesive zone model has been applied in different computational fracture mechanical investigations. However, effects of the cohesive law on crack simulation results have not been systematically and quantitatively studied. To quantify the influence of the cohesive law, a special cohesive element has been developed and implemented into the commer...

The failure behaviors of a structural Cr–Ni–W steel under gigacycle fatigue were investigated, and a life prediction method based on the crack growth was proposed. The discovery of two failure phenomena, including the coexistence of surface and interior cracks and the coexistence of multiple fish-eyes, verifies the possibility of competing failure....

In the present work the local mechanical behavior and fatigue resistance of the welding material were investigated with help of the instrumented indentation technique in combining with FEM computations. By assuming a power-law strain hardening, the elastic-plastic properties of the welding material were identified from inverse indentation analysis...

A cyclic cohesive zone model (CZM) combined with the extended finite element method for the fatigue crack initiation and propagation in ductile materials was investigated under different loading conditions in C(T) specimens. Detailed experimental verification confirmed the known CZM could not predict effects of the loading ratio in fatigue crack pr...

In the present work the fatigue crack growth in AISI304 specimens is investigated experimentally. In 3D finite element analysis the virtual crack closure technique is applied to calculate distributions and variations of the stress intensity factor along the surface crack front. It is confirmed that the stress intensity factor along the surface crac...

The sinter powder metals have found extensive engineering applications in industry. The mechanical property of sinter metals is characterized by high porosity and micro-cracks. Inelastic behavior of the materials is coupled with micro-crack propagation and coalescence of open voids. The machining of sinter metals has significant influence on materi...

Computational simulations of indentations in elastic-plastic materials showed overestimate in determining elastic modulus using the Oliver & Pharr’s method. Deviations significantly increase with decreasing material hardening. Based on extensive finite element computations the correlation between elastic-plastic material property and indentation ha...

Sintered powder metals have found wide applications in industry. However, the constitutive description under complex loading conditions is an open issue. In the present work, the inelastic deformation mechanisms of sintered iron are investigated using nano-indentation technique. With help of the finite element method, the material behaviour of powd...

In the present paper a cohesive zone model coupled with monotonic and cyclic damage mechanisms for simulating elastic-plastic fracture and fatigue crack growth is introduced and applied for investigating failure processes in compact tension specimens. Fracture and fatigue crack tests are conducted on the compact tension C(T) specimen made of stainl...

In the present paper martensite transformation in stainless steel 304 and its effects to material damage is discussed. The experiments confirm that martensite phase transformation in SS304 can be described by the Santacreu model and shows dependence on the plastic strain and stress triaxiality. The plasticity model with the martensite transformatio...

The finite element method (FEM) is popular in cutting process simulations. Due to large strains and element distortions the FEM simulations are confronted with numerical difficulties. In the present contribution the material point method (MPM) is developed for cutting process simulations. Due to special working condition in cutting, a special conta...

Creep fatigue is the main damage form of engine parts operating under both cyclic mechanical and thermal loading conditions. In the present work time-dependent creep and cycle-dependent fatigue of nickel-based super alloys is discussed. Three different kinds of creep–fatigue life models are investigated for the nickel-based super alloys. Effects of...

Sintered metals have found wide applications in mechanical design for their low manufacturing costs. The present paper deals with a sintered iron powder material (ASC 100.29) which is specially manufactured for experimental and computational investigations. The material has been tested under both monotonic and cyclic loading conditions. Fully rever...

Creep damage is an important failure factor of high-temperature alloy. The fatigue crack growth under elevated temperature of the material is investigated for life prediction. In this paper, the numerical simulation of the crack propagation in nickel-based super alloy, IN718, was presented. A modified creep damage model was employed to accumulate t...

Extended finite element method is widely used to simulate the discontinuity problems, e.g. fatigue crack growth. This paper mainly analyzes the fatigue crack propagation under elevated temperature in nickel-based super alloy with extended finite element method. Cohesive zone model is used to describe the mechanical behavior around the crack tip. A...

The process simulations based on FEM techniques have been investigated for many years, some fundamental problems are still unsolved, e.g. the element size effect on the computational results. In present contribution, orthogonal cutting simulations of AISI4340 steel are considered. The major concerns are accuracy of computational results, influence...

With introducing the strain gradient into plasticity theory, the crack field singularity at the crack tip changes. Characterization of the crack in strain-gradient dependent materials has not found a common consensus. In the present work the crack tip field is systematically investigated within the frame of the strain-gradient plasticity using the...

In conventional cohesive zone models the traction-separation law starts from zero load, so that the model cannot be applied to predict mixed-mode cracking. In the present work the cohesive zone model with a threshold is introduced and applied for simulating different mixed-mode cracks in combining with the extended finite element method. Computatio...

The cohesive model becomes popular in crack analysis for its clear physical background and flexible implementation. The cohesive traction–separation law, however, is a critical point and will generally be empirically assumed. In the present paper the cohesive traction–separation law is investigated based on constrained three-dimensional atomistic s...

It is known that the plasticity models affect characterization of the crack tip fields. To predict failure one has to understand the crack tip stress field and control the crack. In the present work the element-free Galerkin methods for gradient plasticity theories have been developed and implemented into the commercial finite element code ABAQUS a...

The present paper deals with the cyclic hardening plasticity of Distaloy AE. Two classical plasticity models, kinematic and isotropic hardening plasticity, are used to approximate hysteresis loops which are taken from low cycle fatigue experiments. It can be confirmed that the superposition of both models shows the best results. Cyclic stress-strai...

In using complex material models, especially the strain-gradient-dependent damage models, the convergence of the finite element computation increasingly becomes a problem. Due to large strains in damaging elements the computation may often result in non-convergence. For the higher-order gradient plasticity the special element formulation would ofte...

Quantification of shot peening effects in fatigue life prediction becomes increasingly important in industry. The goal of the present work is to find out an engineering method for predicting the residual stress variations and to give a quantitative conservative estimate about the improvement from shot peening. The variations of residual stress caus...

The fatigue crack growth, incorporating effects of shot peening, is investigated using two-dimensional finite element analysis. The cohesive zone model, which takes into account the damage evolution under cyclic load, is adopted in the finite element analysis to simulate the potential fracture surfaces. The effects of shot peening on the fatigue cr...