The vulnerability analysis of cladding usually reflects the performance levels of roof systems under wind uplift failure. But the damage area of roof system under wind uplift failure is often large, ...and this causes difficulty in post-disaster reconstruction. In this study, the vulnerability analysis of a roof system was conducted considering the multistage performance levels during the wind uplift failure process of the roof system. First, based on a study on the wind uplift failure mechanism of the roof system, the failure process was divided into four stages according to the deformation of the roof system components and the change in structural responses. Second, the classification criteria and restoration measures corresponding to three-stage performance levels (moderate damage, severe damage, and failure) of the roof system were proposed based on the results of 50 numerical cases. Third, the damage parameter β was defined as a unified index to quantify the three-stage performance levels. The quantitative results for the numerical cases were consistent, and the damage parameter β values were 0.4, 0.73, and 1.0 respectively. Finally, the uncertainty of material properties was considered, and the Latin hypercube sampling was performed to generate structural samples. On this basis, 7000 load–structure samples were analyzed using numerical methods, and the vulnerability curves of the roof system were obtained by fitting the numerical calculations result using the least-squares method. The vulnerability curves can be used as a reference for selecting roof system models and adopting restoration measures after a disaster based on the engineering requirements.
•The three-stage performance levels of the roof system are defined based on the wind uplift failure process.•The damage parameter β is defined as a unified index to quantify the three-stage performance levels.•Considering the three-stage performance levels of roof system in the process of usage, the wind vulnerability analysis is carried out.•Comparing the vulnerability of different types of roof systems, so as to serve the engineering.
The fretting problem occurs at two contact surfaces sustaining small relative displacement, and it reduces the fatigue lifetime dramatically. Estimating accurate fretting fatigue lifetime plays an ...important role in engineering applications. Due to the complicated stress state, and high-stress gradient in the contact surface, the average methods are necessary to obtain the precise lifetime, but the critical distance for the average zone is difficult to estimate. In this work, Artificial Neural Network (ANN) tool combined with damage parameters is proposed to determine the optimal critical distance for different fretting conditions. This tool can also be used to accurately predict the crack initiation lifetime. The fretting fatigue lifetimes calculated by using this approach have shown good agreement with experimental results from literatures. In addition, rough estimates of critical distance for different cases are made based on the numerical results.
•A generalization of the Castillo-Canteli probabilistic fatigue model is proposed.•Generalized fatigue damage variables are proposed keeping original model structure.•Fatigue damage parameters for ...uniaxial and multiaxial loading conditions are discussed.•Experimental fatigue data demonstrated appropriateness of proposed generalization.
This paper proposes a generalization of the Castillo and Fernández-Canteli probabilistic fatigue model and shows how most fatigue models can be obtained as particular cases. Models that include mean-stress effects and multiaxial loading conditions are considered as examples of this general framework. Several fatigue damage parameters such as the Smith-Watson-Topper, the Walker-like strain, energy-based parameter in uniaxial and multiaxial loading conditions, and multiaxial critical plane parameters are proposed as reference parameters for the probabilistic model. It is shown that the Castillo & Fernández-Canteli probabilistic approach can be successfully extended to these advanced fatigue models.
Display omitted
•A modified generalized strain energy (MGSE) criterion for multiaxial fatigue analysis.•Comparative study on critical plane criteria for ductile/brittle materials.•Proposed MGSE ...criterion yields better predictions for ductile/brittle materials.•Modified SWT criterion provides accurate predictions only for brittle materials.
This paper conducts a comparative evaluation on typical critical plane criteria, including Fatemi-Socie, Wang-Brown, modified Smith-Watson-Topper (MSWT) and proposed modified generalized strain energy (MGSE) criteria for multiaxial fatigue analysis of ductile/brittle materials. Experimental datasets of four materials under uniaxial tension, torsion and proportional/non-proportional multiaxial loadings are introduced for model comparison. This study results indicate that criteria with additional material constants yield robust life predictions for different materials. Moreover, the criteria with shear and uniaxial fatigue properties are respectively suitable for ductile and brittle materials, particularly the MGSE superior to others for ductile/brittle materials while MSWT only for brittle materials.
•A damage model is proposed for SAC305 based on irreversible entropy generation.•Damage evolution is more associated with strain rate rather than temperature.•Relationship between microstructure and ...mechanical degradation is elucidated.•Thermal energy and fatigue damage induce morphology evolution and crack formation.
Low-cycle thermal-mechanical fatigue loadings induce progressive and permanent degradation of mechanical properties of lead-free solder materials, and thus reduce the fatigue life of electronic devices. In this study, damage evolution and accumulation of Sn-3.0Ag-0.5Cu (SAC305), the most successfully commercialized lead-free solder material, was investigated by performing strain-controlled fatigue tests at different temperatures (288–373 K) and strain rates (0.001–0.004 s−1). Unlike existing empirical models, a fatigue damage model was proposed based on entropy generation related to the thermodynamic nature of fatigue damage. To be intrinsic to entropy generation, the proposed model was calibrated with the peak stress degradation at different temperatures and strain rates. Our findings showed that the damage parameter is closely related to temperature and strain rate and monotonically increases from 0 to 1 during the low-cycle fatigue loading, which unveiled the fact regarding the irreversibility of the internal entropy generation. For the first time, the damage evolution is found to be more associated with the applied strain rate than the temperature. By observations using an optical microscopy, the physical damage mechanism is elucidated for SAC305 solder by correlating microstructures and damage evolutions. The evolving dendritic β-Sn phase and the surrounding Sn-Ag-Cu ternary eutectic network also explained the effects of temperature and strain rate based on the energy dissipation. Our proposed damage model reconciled the damage accumulation of SAC305 solder subjected to the low-cycle fatigue loading, which is readily adopted to predict the fatigue life of the electronic packaging structures.
Display omitted
This paper studies the multiaxial fatigue behaviour of maraging steel samples produced by selective laser melting. Hollow cylindrical specimens with transverse circular holes are subjected to ...different in-phase bending-torsion loading scenarios. Fatigue crack initiation sites and fatigue crack angles are predicted from the first principal stress field. Fatigue lifetime is computed using a straightforward approach, based on a one-parameter damage law, developed via uniaxial low-cycle fatigue tests. The cyclic plasticity at the notch-controlled process zone is accounted for by combining the equivalent strain energy density concept and the theory of critical distances within a linear-elastic framework. Regardless of the multiaxial loading scenario, experimental observations and predicted lives are very well correlated.
Display omitted
•Multiaxial fatigue behaviour was significantly affected by the bending moment to the torsion moment ratio.•Un-melted regions at surface and subsurface were the main cause of fatigue crack initiation at the notch.•Fatigue crack initiation sites and fatigue crack angles were predicted from the first principal stress field.•Multiaxial fatigue life was successfully predicted using an uniaxial one-parameter damage law.
A new modelling framework is proposed to predict the inelastic features in elastomers’ mechanical behaviour such as the Mullins effect, the permanent set and the induced anisotropy. While based on ...the pseudo-elasticity theory, our model departs from the classical theory on three counts: (i) a separable damage parameter Ω, separable in the principal stretches, is devised and incorporated to facilitate capturing the induced anisotropy; (ii) the damage variable is directly incorporated into the hyperelastic strain energy function to capture the permanent set, and (iii) a specific functional form for the damage parameter is considered, conducive to modelling the foregoing behaviours. The devised framework is then specialised using a recently proposed strain energy function W and is validated against various experimental datasets ranging from filled natural and silicon rubbers, to synthetic rubbers and hydrogels. It is shown that the proposed model favourably captures the inelastic behaviours of interest exhibited by the specimens, and the devised modelling framework facilitates obtaining those favourable fits via a reduced number of model parameters compared with the existing theories in the literature. The proposed framework may also be used directly in conjunction with other strain energy functions for a versatile modelling of the Mullins effect in the finite deformation of rubber-like materials.
•A new modelling framework for capturing the Mullins effect in elastomers.•Incorporating discontinuous softening, permanent set and the induced anisotropy.•Devising a novel separable (in principal stretches) damage parameter.•Application to a wide range of elastomers including filled rubbers and hydrogels.•Accurate modelling results with a low number of parameters and computational costs.
This article is an analytical review of experimental and theoretical studies of creep and creep rupture strength of metals under unsteady complex stress states published over the past 60 years.The ...first systematic studies of the creep of metals under complex stress conditions were published in the late 50s and early 60s of the 20th century in the Soviet Union (L. M. Kachanov and Yu. N. Rabotnov) and Great Britain (A. E. Johnson). Pioneering work on creep rupture strength first appeared in the USSR (L. M. Kachanov and Yu. N. Rabotnov). Subsequently, Yu. N. Rabotnov developed the kinetic theory of creep and creep rupture strength, with the help of which it is possible to efficiently describe various features of the creep process of metals up to fracture under various loading programs. Different versions of the kinetic theory use either a scalar damage parameter, or a vector parameter, or a tensor parameter, or a combination of them. Following the work of M. Kachanov and Yu. N. Rabotnov mechanics of continuum destruction began to develop in Europe, in Asia, and then in the USA.The hypothesis of proportionality of stress deviators and deviators of creep strain rates is accepted as the main connection between the components of stress tensors and creep strains. When modeling experimental data, the proportionality coefficient in this dependence takes different forms. The main problem in the development of this direction is the difficulty in obtaining experimental data with arbitrary loading programs.This review provides the main results of studies conducted by scientists from different countries. Except Yu. N. Rabotnov and L. M. Kachanov, also a significant contribution to the development of the direction of science made by Russian scientists N. N. Malinin, A. A. Ilyushin, V. S. Namestnikov, S. A. Shesterikov, A. M. Lokoshchenko, Yu. P. Samarin, O. V. Sosnin, A. F. Nikitenko, et al.
Li2O-Al2O3-SiO2 transparent glass-ceramics (LAS-TGCs) are promising candidates for transparent armour materials due to their excellent physical and mechanical capabilities. In this work, the dynamic ...behaviour of a LAS-TGC were further investigated using the planar impact technique and photon Doppler velocimetry. The shock stress, shock wave velocity, failure wave velocity and spall strength were obtained. In addition, the recompression signal, as a signature of failure waves, was observed to evolve into an oscillation signal as the impact stress decreases, indicating that the failure wave is gradually formed at a threshold. It has been noted that the failure wave velocity decreases with the increase in external loading and then turns upwards. The damage parameter of the LAS-TGC was assessed to be 0.410(5) under a shock stress of ~5.5 GPa, which is smaller than that of K9 glass. It is suggested that the LAS-TGC has better shock resistance than K9 glass.
•A LAS-TGC was prepared via two-step heat treatment.•Planar impact experiments were conducted on the LAS-TGC.•The shock stress, shock wave velocity, failure wave velocity, and spall strength were obtained.•The failure wave is gradually formed at a threshold.•The LAS-TGC has better shock resistance than K9 glass.
PDF
