Xiaosheng Gao

University of Akron, Akron, Ohio, United States

Are you Xiaosheng Gao?

Claim your profile

Publications (34)22.29 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the major drawbacks of the Gurson-type of porous plasticity models is the inability of these models to predict material failure under low stress triaxiality, shear dominated conditions. This study addresses this issue by combining the damage mechanics concept with the porous plasticity model that accounts for void nucleation, growth and coalescence. In particular, the widely adopted Gurson–Tvergaard–Needleman (GTN) model is extended by coupling two damage parameters, representing the volumetric damage (void volume fraction) and the shear damage, respectively, into the yield function and flow potential. The effectiveness of the new model is illustrated through a series of numerical tests comparing its performance with existing models. The current model not only is capable of predicting damage and fracture under low (even negative) triaxiality conditions but also suppresses spurious damage that has been shown to develop in earlier modifications of the GTN model for moderate to high triaxiality regimes. Finally the modified GTN model is applied to predict the ductile fracture behavior of a beta-treated Zircaloy-4 by coupling the proposed damage modeling framework with a recently developed J2–J3 plasticity model for the matrix material. Model parameters are calibrated using experimental data, and the calibrated model predicts failure initiation and propagation in various specimens experiencing a wide range of triaxiality and Lode parameter combinations.
    International Journal of Solids and Structures 09/2014; 51(18):3273–3291. · 1.87 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Zirconium alloys such as Zircaloy-4 are used in nuclear applications due to adequate strength, ductility and resistance to radiation damage. Recent modeling efforts have focused on improvements to the predicted elastic-plastic response, complicated by the strong strength-differential (S-D) effects in HCP materials. This study develops a pressure-insensitive, continuum plasticity model, dependent on the second and third invariants of the stress deviator (J2 and J3), with an internal variable related to the plastic strain to describe the tension-compression asymmetry of a β-treated Zircaloy-4. Plastic deformation drives isotropic and distortional hardening of the non-Mises yield surface. The proposed plasticity model has been calibrated and validated using measured results from an experimental test program. Results show that the proposed model captures the complex elastic-plastic response observed in measured load-displacement and torque-rotation curves over a range of triaxiality and Lode parameter values.
    07/2014; 451(1-3).
  • Jun Liu, Yulong Li, Xiaosheng Gao
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study, experiments of bird impact with a flat plate are conducted at different striking velocities and simulated using an explicit finite element software PAM-CRASH with three bird material models. The predicted displacement and strain in the plate and impact reaction force on the clamping fixture are compared with experimental measurements. The results suggest that the elastic-plastic material model with a defined failure strain is best suited for bird strike simulation at low impact velocities, the isotropic elastic-plastic hydrodynamic solid model is best suited for bird strike simulation at intermediate impact velocities, and the SPH (smooth particle hydrodynamic) method with the Murnaghan EOS (equation of state) for solid element is best suited for bird strike simulation at high impact velocities. Using the appropriate bird material model, the simulation results agree very well with experimental data.
    International Journal of Impact Engineering 01/2014; · 1.68 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Zirconium alloys such as Zircaloy-4 are used in nuclear applications due to adequate strength, ductility and resistance to radiation damage. Recent modeling efforts have focused on improvements to the predicted elastic–plastic response, complicated by the strong strength-differential (S-D) effects in HCP materials. This study develops a pressure-insensitive, continuum plasticity model, dependent on the second and third invariants of the stress deviator (J2 and J3), with an internal variable related to the plastic strain to describe the tension–compression asymmetry of a β-treated Zircaloy-4. Plastic deformation drives isotropic and distortional hardening of the non-Mises yield surface. The proposed plasticity model has been calibrated and validated using measured results from an experimental test program. Results show that the proposed model captures the complex elastic–plastic response observed in measured load–displacement and torque–rotation curves over a range of triaxiality and Lode parameter values.
    Journal of Nuclear Materials. 01/2014; 451(s 1–3):292–299.
  • Jun Zhou, Matthew Hayden, Xiaosheng Gao
    [Show abstract] [Hide abstract]
    ABSTRACT: This article presents a comprehensive experimental and numerical study to investigate the effects of strain rate and temperature on flow stress and ductile failure strain of three aluminum alloys. The test matrix includes smooth and notched round tensile specimens tested at room temperature (24 ℃) and two elevated temperatures (66 ℃ and 149 ℃), and under different strain rates. For 5083-H116, three loading rates are considered at 24 ℃ and it is found that the flow stress and failure strain are lowest at the intermediate strain rate. At high strain rate, the flow stresses of 5083-H116 and 6082-T6 are higher than the quasi-static loading while the flow stress of the 5183 weld metal remains unchanged; the ductility of the 5XXX alloys shows a significant increase compared to the quasi-static loading while the ductility of 6082-T6 does not change much. The study indicates that the Johnson–Cook plasticity and fracture models can be used to describe the temperature dependencies of the flow stress and the failure strain for 6082-T6 but not the 5XXX alloys. At 66 ℃ the 5XXX alloys do not display temperature softening compared to 24 ℃ while their ductility is reduced. As temperature is elevated to 149 ℃, the flow stress of the 5XXX alloys decreases while the ductility increases. The unconventional behavior of the 5XXX alloys in certain temperature and strain rate ranges has been attributed to the dynamic strain aging effect. The study also suggests that the dependency of the failure strain on stress triaxiality can be described by the Johnson–Cook fracture model for all three materials under quasi-static loading at room temperature and the model parameters are calibrated using an inverse method combining experimental results with finite element analysis.
    ARCHIVE Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989-1996 (vols 203-210) 05/2013; 227(5):883-895. · 0.63 Impact Factor
  • Source
    Shihao Hu, Zhenhai Xia, Xiaosheng Gao
    [Show abstract] [Hide abstract]
    ABSTRACT: The adhesion and friction coupling of hierarchical carbon nanotube arrays was investigated with a hierarchical multiscale modeling approach. At device level, vertically aligned carbon nanotube (VA-CNT) arrays with laterally distributed segments on top were analyzed via finite element methods to determine the macroscopic adhesion and friction force coupling. At the nanoscale, molecular dynamics simulation was performed to explore the origin of the adhesion enhancement due to the existence of the laterally distributed CNTs. The results show interfacial adhesion force is drastically promoted by interfacial friction force when a single lateral CNT is being peeled from an amorphous carbon substrate. By fitting with experiments, we find that under shearing loadings the maximum interfacial adhesion force is increased by a factor of ~5, compared to that under normal loadings. Pre-existing surface asperities of the substrate have proven to be the source of generating large interfacial friction, which in turn results in an enhanced adhesion. The critical peeling angles derived from the continuum and nano- levels are comparable to those of geckos and other synthetic adhesives. Our analysis indicates that the adhesion enhancement factor of the hierarchically structured VA-CNT arrays could be further increased by uniformly orienting the laterally distributed CNTs on top. Most importantly, a significant buckling of the lateral CNT at peeling front is captured on the molecular level, which provides a basis for the fundamental understanding of local deformation, and failure mechanisms of nanofibrillar structures. This work gives an insight into the durability issues that prevent the success of artificial dry adhesives.
    ACS Applied Materials & Interfaces 03/2012; 4(4):1972-80. · 5.01 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Developments in computational mechanics have given engineers tools to predict the evolution of damage in complex structures. Damage models have been developed that relate failure strain to stress triaxiality and Lode angle. Calibration of these models has traditionally relied on specimens that exhibit high triaxiality and limited Lode angle. This paper presents a specimen that can be tested in combined tension and torsion to achieve low triaxiality over a range of Lode angle. Numerical analysis of the specimen shows that it exhibits uniformity of stress–strain and stable values of triaxiality and Lode angle as plastic strain develops, both of which are desirable characteristics for calibration of ductile failure models. The design of a new displacement and rotation gage is presented that allows non-contact measurement at the gage section. Experimental results are used to develop the failure surface for 5083 aluminum.
    International Journal of Mechanical Sciences - INT J MECH SCI. 01/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: It has been shown that the plastic response of many materials, including some metallic alloys, depends on the stress state. In this paper, we describe a plasticity model for isotropic materials, which is a function of the hydrostatic stress as well as the second and third invariants of the stress deviator, and present its finite element implementation, including integration of the constitutive equations using the backward Euler method and formulation of the consistent tangent moduli. Special attention is paid for the adoption of the non-associated flow rule. As an application, this model is calibrated and verified for a 5083 aluminum alloy. Furthermore, the Gurson–Tvergaard–Needleman porous plasticity model, which is widely used to simulate the void growth process of ductile fracture, is extended to include the effects of hydrostatic stress and the third invariant of stress deviator on the matrix material.
    International Journal of Plasticity - INT J PLASTICITY. 01/2011; 27(2):217-231.
  • Haodan Jiang, Xiaosheng Gao, T. S. Srivatsan
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a cohesive zone model and explores its capacity for predicting crack growth in materials and structures. An exponential cohesive law was implemented for the specific case of monotonic loading and applied to crack growth simulation, in three-dimensions, in thin fracture specimens made from the chosen material of interest. The cohesive law is governed by the two parameters, cohesive strength and cohesive energy, and our parameter study revealed the cohesive strength to be a more influential parameter. The cohesive parameters were calibrated for the commercial aluminum-copper-magnesium alloy 2024 in the T3 temper by comparing the finite element predictions with experimental test results obtained for a compact-tension specimen. Middle-cracked tension test specimens having different ratios of the crack length were modeled using the calibrated parameters and the numerical results showed good correlation with the experimental test results.
    Neural, Parallel and Scientific Computations 09/2010; 18(3-4):291-306.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: With unique hierarchical fibrillar structures on their feet, gecko lizards can walk on vertical walls or even ceilings. Recent experiments have shown that strong binding along the shear direction and easy lifting in the normal direction can be achieved by forming unidirectional carbon nanotube array with laterally distributed tips similar to gecko's feet. In this study, a multiscale modeling approach was developed to analyze friction and adhesion behaviors of this hierarchical fibrillar system. Vertically aligned carbon nanotube array with laterally distributed segments at the end was simulated by coarse grained molecular dynamics. The effects of the laterally distributed segments on friction and adhesion strengths were analyzed, and further adopted as cohesive laws used in finite element analysis at device scale. The results show that the laterally distributed segments play an essential role in achieving high force anisotropy between normal and shear directions in the adhesives. Finite element analysis reveals a new friction-enhanced adhesion mechanism of the carbon nanotube array, which also exists in gecko adhesive system. The multiscale modeling provides an approach to bridge the microlevel structures of the carbon nanotube array with its macrolevel adhesive behaviors, and the predictions from this modeling give an insight into the mechanisms of gecko-mimicking dry adhesives.
    ACS Applied Materials & Interfaces 09/2010; 2(9):2570-8. · 5.01 Impact Factor
  • Sunil Prakash, Xiaosheng Gao, T. S. Srivatsan
    [Show abstract] [Hide abstract]
    ABSTRACT: The fracture response of mild steel in the domain of brittle behavior, i.e., the cleavage range, has been carefully evaluated using a weakest link statistical model, assuming the existence of a distribution of cracked carbide particles in the microstructures. Experiments have provided an evidence of both scatter in test results and the existence of constraints. Statistical-based model to include micromechanics were developed in an attempt to study and analyze the problem. The Weibull stress micro-mechanical model was used in this study to quantify the constraint effects. This was done numerically using a constraint function (g(M)) derived from the Weibull stress model. The non-dimensional function (g(M)) describes the evolution of the effects of constraint loss on fracture toughness relative to the reference condition, i.e., plane-strain, small scale yielding (SSY) (T-stress = 0). Single-edge SE(B) notched bending specimens having different crack lengths, different cross-sections and side-grooves were modeled and the constraint function (g(M)) was calculated. In this paper, we compare the loss in constraint for both the deep notch and shallow notch specimens for a given cross-section of the single-edge notched bend specimen (SE(B)).
    Neural, Parallel and Scientific Computations 03/2010; 18(1):33-46.
  • Xiaosheng Gao
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper summarizes recent studies on application of the Weibull stress model to predict cleavage fracture of structural components under dynamic loading. Two pressure vessel steels, the strongly rate-sensitive A515-70 steel and the moderately rate-sensitive Euro material (22NiMoCr37), are considered in the investigation. The results, based on independent calibrations at different loading rates, demonstrate that the Weibull modulus (m) is invariant of loading rate for both materials. While m remains a constant for each material, σu decreases and σw–min increases with higher loading rates. The studies also show that dynamic loading reduces constraint loss, i.e., it drives the response towards the small-scale yielding configuration, and this rate effect tends to saturate at higher loading rate. The demonstrated loading rate invariance of m, when combined with the Master Curve for dynamic loading, can provide a practical approach which simplifies the process to estimate σu as a function of loading rate.
    International Journal of Pressure Vessels and Piping. 01/2010;
  • Source
    Xiaosheng Gao, Guihua Zhang, Charles Roe
    [Show abstract] [Hide abstract]
    ABSTRACT: The main purpose of this paper is to demonstrate that besides the stress triaxiality parameter, the Lode angle, which can be related to the third invariant of the deviatoric stress tensor, also has an important effect on ductile fracture. This is achieved by conducting a series of micromechanics analyses of void-containing unit cells and experimental-numerical studies of carefully designed specimens experiencing a wide range of stress states. As a result, a fracture criterion is expressed in terms of the equivalent failure strain as a function of the stress triaxiality and the Lode angle (or the third invariant of the stress deviator) and this function is calibrated for a DH36 steel plate.
    International Journal of Damage Mechanics 01/2010; 19(1):75-94. · 1.75 Impact Factor
  • Haodan Jiang, Xiaosheng Gao, T.S. Srivatsan
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes an irreversible cohesive zone model to simulate fatigue crack growth. The model includes a three-dimensional (3-D) cohesive law that follows a distinct loading/unloading path and a damage evolution mechanism that reflects a gradual degradation of cohesive properties of the material under the influence of cyclic loading. To overcome convergence difficulties arising from nonlinearity of the cohesive zone model, the stabilization technique and the viscous regularization of the constitutive law are employed. For high-cycle fatigue applications, a damage extrapolation scheme is adopted to reduce computational cost. The irreversible cohesive zone model is implemented in the finite element software ABAQUS through a user defined subroutine and is used to predict fatigue crack growth in a compact-tension-shear (CTS) specimen with an emphasis on the extrinsic influence of overload for different loading modes. The numerical results show good agreement with experimental records documented in the open literature and capture the essential features of fatigue crack growth for various loading conditions. This indicates that the irreversible cohesive zone model can serve both as an accurate and efficient tool for the prediction of fatigue crack growth.
    Finite Elements in Analysis and Design 08/2009; 45(10):675-685. · 1.39 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The experimental and numerical work presented in this paper reveals that stress state has strong effects on both the plastic response and the ductile fracture behavior of an aluminum 5083 alloy. As a result, the hydrostatic stress and the third invariant of the stress deviator (which is related to the Lode angle) need to be incorporated in the material modeling. These findings challenge the classical J2 plasticity theory and provide a blueprint for the establishment of the stress state dependent plasticity and ductile fracture models for aluminum structural reliability assessments. Further investigations are planned to advance, calibrate and validate the new plasticity and ductile fracture models.
    International Journal of Plasticity. 01/2009;
  • B. A. Young, Xiaosheng Gao, T. S. Srivatsan
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we compare and contrast the crack growth rate of a nickel-base superalloy (Alloy 690) in the Pressurized Water Reactor (PWR) environment. Over the last few years, a preponderance of test data has been gathered on both Alloy 690 thick plate and Alloy 690 tubing. The original model, essentially based on a small data set for thick plate, compensated for temperature, load ratio and stress-intensity range but did not compensate for the fatigue threshold of the material. As additional test data on both plate and tube product became available the model was gradually revised to account for threshold properties. Both the original and revised models generated acceptable results for data that were above 1 × 10−11 m/s. However, the test data at the lower growth rates were over-predicted by the non-threshold model. Since the original model did not take the fatigue threshold into account, this model predicted no operating stress below which the material would effectively undergo fatigue crack growth. Because of an over-prediction of the growth rate below 1 × 10−11 m/s, due to a combination of low stress, small crack size and long rise-time, the model in general leads to an under-prediction of the total available life of the components.
    Journal of Nuclear Materials 01/2009; 394:63-66. · 1.21 Impact Factor
  • Journal of ASTM International 01/2008; 5(9).
  • Xiaosheng Gao, James A. Joyce, Charles Roe
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper examines the dependence of the Weibull stress parameters on loading rate for a 22NiMoCr37 pressure vessel steel. Extensive fracture tests, including both quasi-static and dynamic tests, are conducted using deep- and shallow-cracked SE(B) specimens. The fracture specimens are carefully prepared to ensure the crack fronts are placed at the location where the material is homogeneous. Three dynamic loading rates (in terms of the stress intensity factor rate, in the low-to-moderate range are considered. The load-line velocities for the dynamic tests are chosen so that the resulted values for the deep- and shallow-cracked specimens are the same. Independent calibrations performed at each loading rate (quasi-static and the three dynamic loading rates) using deep- and shallow-cracked fracture toughness data show that the Weibull modulus, m, is invariant of loading rate. The calibrated m-value is 7.1 for this material. Rate dependencies of the scale parameter (σu) and the threshold parameter (σw-min) are computed using the calibrated m and the results indicate that σu decreases and σw-min increases with higher loading rates. The demonstrated loading rate invariant of m, when combined with the master curve for dynamic loading, can provide a practical approach which simplifies the process to estimate σu as a function of loading rate.
    Engineering Fracture Mechanics. 01/2008;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, the corrosion-fatigue data on Alloy 690 plate documented in the open literature is compared with test data obtained using steam generator tubing. The results on plate material documented in the open literature is not representative of actual behavior of steam generator tubing due to the mutually interactive influences of microstructural features, section thickness and processing variables. This paper also examines if response of steam generator tubing in a pressurized water reactor environment can be modeled using test data obtained for the material on plate stock. The fatigue crack growth rate data for alloy IN 690 used in actual steam generator tubing in low dissolved oxygen PWR environment was generated using a circumferentially through-wall cracked tube specimen. The laboratory test data is compared with the data published in the open literature using a modified corrosion-fatigue model. Test results reveal the tube material to have near similar fatigue crack growth rate behavior when compared to the plate material. This provides conclusion that the standard specimen geometry, such as compact tension specimen, can be used to characterize the response of the tube in adverse environments.
    Materials & Design. 01/2007;
  • Source
    Jinkook Kim, Guihua Zhang, Xiaosheng Gao
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper summarizes our recent studies on modeling ductile fracture in structural materials using the mechanism-based concepts. We describe two numerical approaches to model the material failure process by void growth and coalescence. In the first approach, voids are considered explicitly and modeled using refined finite elements. In order to predict crack initiation and propagation, a void coalescence criterion is established by conducting a series of systematic finite element analyses of the void-containing, representative material volume (RMV) subjected to different macroscopic stress states and expressed as a function of the stress triaxiality ratio and the Lode angle. The discrete void approach provides a straightforward way for studying the effects of microstructure on fracture toughness. In the second approach, the void-containing material is considered as a homogenized continuum governed by porous plasticity models. This makes it possible to simulate large amount of crack extension because only one element is needed for a representative material volume. As an example, a numerical approach is proposed to predict ductile crack growth in thin panels of a 2024-T3 aluminum alloy, where a modified Gologanu–Leblond–Devaux model [Gologanu, M., Leblond, J.B., Devaux, J., 1993. Approximate models for ductile metals containing nonspherical voids – Case of axisymmetric prolate ellipsoidal cavities. J. Mech. Phys. Solids 41, 1723–1754; Gologanu, M., Leblond, J.B., Devaux, J., 1994. Approximate models for ductile metals containing nonspherical voids – Case of axisymmetric oblate ellipsoidal cavities. J. Eng. Mater. Tech. 116, 290–297; Gologanu, M., Leblond, J.B., Perrin, G., Devaux, J., 1995. Recent extensions of Gurson’s model for porous ductile metals. In: Suquet, P. (Ed.) Continuum Micromechanics. Springer-Verlag, pp. 61–130] is used to describe the evolution of void shape and void volume fraction and the associated material softening, and the material failure criterion is calibrated using experimental data. The calibrated computational model successfully predicts crack extension in various fracture specimens, including the compact tension specimen, middle crack tension specimens, multi-site damage specimens and the pressurized cylindrical shell specimen.
    International Journal of Solids and Structures - INT J SOLIDS STRUCT. 01/2007; 44(6):1844-1862.