Property Degradation Model Research Articles

Research on mechanical property degradation model of equipment compartment floor under atmospheric corrosion condition

A mechanical property degradation model of material fatigue life varying with stress level and corrosion time was developed in this study. An acidified NaCl solution was used to accelerate the corrosion of stainless-steel samples, and the relationship between laboratory-accelerated corrosion and atmospheric corrosion was established using corrosion thickness loss parameters. Based on the results of a pre-corroded fatigue test, lgN–S–T surface models and a modified version of Miner’s rule for calculating nonlinear mechanical damage accumulation were proposed. Taking a real part of a high-speed train as an example, critical operating mileages considering material fatigue performance degradation under corrosion conditions were calculated, which were consistent with failure mileages of the census results.

Mechanical Property Degradation and Prediction Model of Red Sandstone Under Action of Dry–Wet Cycles in Acid Environment

Mechanical Property Degradation and Prediction Model of Red Sandstone Under Action of Dry–Wet Cycles in Acid Environment

A novel creep-fatigue life evaluation method for ceramic-composites components

A novel progressive creep-fatigue damage analysis method based on multiscale information was proposed to accurately predict the service life of SiC/SiC composites and their structural components under complex mechanical loads and external environments. First, the strength degradation of SiC fibers involving five damage mechanisms and degradation of the properties of the interface under high-temperature fatigue loading were described quantitatively based on experimental results. Subsequently, a micromechanical model incorporating the global load sharing model, two-parameter Weibull model, shear-lag model, property degradation models of various constituents, and the effect of the braiding angle was utilized to calculate the volume fraction of broken fibers. The fatigue life of 3D 4-directional SiC/SiC composites was predicted and exhibited a trend similar to that of the experimental data. The rupture life of the SiC/SiC composites was calculated considering the stress transfer among microscopic constituents and the influence of creep slow crack growth on the fiber strength. The volume fraction of broken fibers obtained in these micromechanical models was used to perform a gradual strength degradation in the novel progressive creep-fatigue damage analysis method. Microscopic constituents damage and macroscopic property degradation were quantitatively linked in this step. This infuses the micro information into the traditional phenomenological progressive damage method. The gradual stiffness degradation rules were derived from the fitting of the residual elastic modulus obtained from the fatigue and creep experiments. Finally, the damage evolution and service life of SiC/SiC turbine blades were simulated and evaluated as a preliminary validation of the entire process.

A material property degradation model of composite laminates considering stress level

Conventional phenomenological models of composite laminates often require a large amount of experimental data due to the dependence on stress level. In this study, a new generalized model capable of predicting the material property degradation at each stress level using a single set of parameters is proposed to dramatically subside the experimental cost. Furthermore, two sets of residual strength data and one set of residual stiffness data are adopted to validate the proposed model. The results show that the new model is capable of predicting both residual strength and stiffness at arbitrary stress levels using single set of model parameters.

Implementation of progressive failure for fatigue based on cycle-dependent material property degradation model

Anisotropic composite materials have been extensively utilized in mechanical, automotive, aerospace and other engineering areas due to high strength/weight ratio, superb resistance to corrosion and excellent thermos-mechanical properties. As the use of composite materials increases, determination of material properties, mechanical analysis and failure of the structure become essential for the design of composite structure. In particular, the fatigue failure is important to ensure that structures can survive in harsh environmental conditions. The non-homogeneous character of composites induces diverse failure modes of the constituent including fiber fracture, matrix cracking, fiber-matrix interface failure, and delamination, which makes their fatigue behavior very complex in comparison with traditional engineering materials. In this study, based on different failure modes of a unidirectional ply under multiaxial stress states, a progressive damage theory is extended to simulate fatigue failure in composite laminates subjected to cyclic loadings. A cycle-dependent material property degradation model was employed to predict deterioration of the material properties due to arbitrary stress state and ratio. This cycle-dependent material property degradation rule is implemented into user subroutine USDFLD in ABAQUS through which cycle-dependent material degradation states are updated over fatigue loading. The present computational implementation is tested by comparing the experimental fatigue behavior of a 30-degree off-axis specimen with the simulation result obtained by the present implantation. The comparison between the experimental and simulation results demonstrates the successful simulation capability of the present implementation.

Multiscale study on determining representative volume elements size for mechanical behaviours of complex polymer nanocomposites with nanoparticulate agglomerations

Representative volume elements (RVE) have been widely employed to describe and predict the various effective properties of heterogeneous composite systems. In this present study with an interphase property degradation model, a multiscale analysis is performed to investigate the mechanical behaviours of polymer nanocomposites containing nanoparticulate agglomerations. Using the Fourier transform approach on the structural property variation at given cell lengths, the smallest RVE size (the minimum allowable length for an approximate description of the material system) is determined based on the coefficient of variation. It is reasonable to select an RVE size that is equal to a quarter of the most dominant wavelength as the minimum RVE size. A novel user-defined factor-based approach similar to the concept of margin of error is proposed to determine the optimal sampling number at a specific RVE size. The precision approach can provide accurate estimation of the mechanical properties of the nanocomposites with reduced computational cost.

Thermo-mechanical characterisation and modelling of GFRP laminated aluminium

This paper aims to propose a thermo-mechanical model to predict and evaluate the variation of mechanical and interlaminar fracture properties at elevated temperatures. Tensile, compression, and shear tests were conducted on glass fibre reinforced polymer composite while double-cantilever beam and end notched flexural tests were conducted on GFRP laminated aluminium samples using a thermostatic chamber at 30, 70, and 110 °C. A modified property degradation model was then fitted to predict the current results and verified with the existing data. Degradation of properties is mainly attributed to the softening of epoxy, evident in Mode-I fracture toughness, shear strength, and matrix-orientated strengths. The proposed model is specifically effective in fitting elevated temperatures, but not for temperatures below room temperature. The degradation model may project data with good fit and describe the trend of properties effectively with a single fitting parameter.

Progressive failure analysis of woven composites considering structural characteristics based on micro-mechanics

In this study, a three-dimensional progressive failure model was developed to predict the mechanical response of woven composites. For the formulation of progressive failure, a material property degradation model was designed, which was based on the three-dimensional Hashin failure criteria. Failure modes such as fiber breakage and matrix failure were considered. Woven composite models with different weave patterns and fiber volume fractions were created as the representative volume element (RVE). The cross sections of the RVE were modeled from scanning electron microscope observations. To prove the validity of the proposed model, the plain and twill-woven composite were fabricated by a vacuum-assisted resin transfer molding process with respect to fiber volume fraction. Mechanical tensile, compression, and shear tests were conducted and fractography was investigated. As a result, good correlation between the predicted properties from the progressive failure simulation and the experimental results, such as stress-strain curve and the failure modes, was achieved.

Life prediction of a notched composite ring using progressive fatigue damage models

In this paper, a progressive fatigue damage modeling technique is proposed based on Reifsnider's critical element concept. The static and fatigue behavior of the unidirectional E-glass/epoxy composite plies in the fiber and matrix direction is obtained experimentally. Considering suitable material property degradation models, a computer code is developed which integrating with the Abaqus software it is capable of predicting the fatigue life of a notched composite ring with different layup configuration under arbitrary states of stress. To evaluate the applicability of the model, a number of fatigue tests under different states of stress are conducted on the notched composite rings. It is proved that by having unidirectional properties of a composite, this model is capable of estimating the static strength of the notched rings with less than five percent deviation and putting forward a reliable prediction for fatigue life with less than twenty percent underestimation.

Progressive failure behavior of composite flywheels stacked from annular plain profiling woven fabric for energy storage

Annular disk flywheels made of plain profiling woven carbon-fiber-reinforced composites possess favorable biaxial strength along radial and circumferential directions to get higher rotation speed and higher energy density in flywheel energy storage system. Each preform disk layer of fabric stacked for the new composite flywheel in our case study was profiling woven with a continuous fill yarn and radial arranged warp yarns in plain woven style. The progressive failure numerical algorithm was applied to reveal the failure phenomenon in fan-shaped representative volume unit of the plain woven fabric composite flywheel under centrifugal load in high speed running. In the numerical simulation of progressive failure, the analytical iterations were compiled with ANSYS-APDL based on 3D Tsai-Wu failure criterion and Reddy’s sudden material property degradation model. The analysis results indicated that the orthogonal plain profiling fabrics enhanced flywheel’s damage tolerance while the radial fiber yarns delayed transvers cracks. Spin experiments of the test flywheels were carried out on the one-point supporting shaft system driven by high speed motor in a vacuum chamber. All eight flywheel samples reached the tangential speed beyond 850 m/s in spin test, exhibiting a good consistency in material performance. The maximum speed was 898 m/s and the corresponding energy storage density was 64.5 W h/kg in the damage limitation spin test of the plain woven composite flywheel. The spin test verified the validity of the biaxial reinforcement using plain fabric by profiling woven method for composite flywheels with thick radial size. Progressive failure analysis simulation was useful in predicting the burst speed of woven fabric composite flywheels.

Three-dimensional progressive failure modeling of glass fiber reinforced thermoplastic composites for impact simulation

In this study, a three-dimensional (3D) progressive failure material model was developed for glass fiber reinforced thermoplastic (GFRP) composites to predict the nonlinear mechanical response under impact loads. For the formulation of progressive failure, the material property degradation model (MDM) was constructed using a continuum damage mechanics (CDM) model based on the 3D Hashin failure criteria. The proposed progressive failure formulations were implemented in the user-defined material model (UMAT) in the commercial nonlinear finite element analysis (FEA) software LS-Dyna. Then, the progressive failure model was verified experimentally with flexural and impact tests. Finally, it was found that the proposed 3D progressive failure model can be used to predict not only damage progression and impact behavior, but also interlaminar delamination.

Dynamic simulation of disintegration of wood chips caused by impact and collisions during the steam explosion pretreatment

Steam explosion (SE) pretreatment produces damaged and disintegrated biomass with a large surface area which facilitates enzymatic hydrolysis for the production of biofuels and other value-added chemicals. It was observed during experiments that wood chips disintegrate into smaller pieces because of collisions and impact with each other and the walls of the SE equipment. In this study, these events were simulated using the finite element method. Wood chips were simulated in this model as a linear elastic material until failure. The damage initiation was identified using Hashin’s damage initiation criteria. Once the damage was initiated, additional loading caused the evolution of damage, i.e. degradation and breakage of the material, which was modelled using the material property degradation model and deletion of the failed elements. Elastic and strength properties of spruce wood were estimated at ambient conditions (12 % moisture content at 20 °C) and at SE conditions (30 % moisture content at 160 °C). Comparison of simulations performed using material properties at ambient and SE conditions revealed that the damage in wood chips significantly increased because of the steam treatment. The effects of wood chip velocity and orientation at the time of impact were studied as well. It was found that wood chips moving at high velocity and impacting with the steel wall in the radial direction acquire the most damage. © 2016, Springer-Verlag Berlin Heidelberg.

Progressive failure analysis of open-hole composite hoops under radial loading

Abstract In this article a finite element-based analysis and experimental study of geometrically non-linear progressive failure analysis of open-hole composite laminated hoops under radial loading is presented. In the finite element analysis the mode-dependent failure criterion Hashin failure criterion and Reddy's sudden material property degradation model are coded using ANSYS-APDL and a progressive failure analysis code is developed. Based on a tensile test machine the experimental fixtures are designed and implemented to apply radial loading on inner surface of the composite hoops. Progressive failure analysis of the sample composite laminated hoops with an open-hole of different diameters subjected to radial loading are performed to study the effect of geometric non-linearity on the failure initiation and propagation. Results show that with large longitudinal strength the circumferential crack is the main failure form because of the shear effect. And, diameters of the open-holes have a significant influence on the initiation and propagation of the failure.

Prediction of Fatigue Life for Single Fastener Joints in Composite Laminates

A progressive damage method of predicting the fatigue life of mechanically fastened joints in fiber-reinforced plastics was established, which is integrated fatigue material property degradation models. The equations of virtual work based on the theory of time increment were deduced to analyze stress-strain states under fatigue loading conditions. The three-dimensional Hashin-type fatigue failure criteria were introduced into the method to detect damage for diverse damage modes. The criteria of the structure catastrophe and the sudden material property degradation rules including the correlation among four basic damage mechanisms were also established. A software module of progressive damage analyses for bolted composite laminates is compiled, which is convenient for the application in engineering. The fatigue life, failure initiation, propagation and catastrophic failure of composite bolted joints under tension-tension fatigue loading conditions are predicted by using the fatigue progressive damage method established in the paper. An excellent agreement is found between data obtained from this study and the experiment.

Review of Degradation Models for Progressive Failure Analysis of Fiber Reinforced Polymer Composites

The success of any progressive failure analysis of composite structures is influenced by the failure criteria and the associated material property degradation models. The failure criteria are the conditions for the prediction of the occurrence of material damage. The degradation models are mathematical representations of the residual properties for each material damage state predicted by the failure criteria. A brief summary of the major classes of failure criteria pertaining to the degradation models is followed by a review of degradation models that have been developed for unidirectional polymer matrix composite laminates. The review is organized around the relationships of the various models to associated failure criteria as well as the various constitutive frameworks for finite element implementation. Models that invoke residual properties as a one-time sudden degradation of the original properties are described followed by models where the mathematical representation of at least one property invokes gradual property degradation as a function of some other evolving field variable.

Progressive Failure Analysis for Prediction of Post-buckling Compressive Strength of Laminated Composite Plates and Stiffened Panels

A progressive failure analysis for prediction of the post-buckling compressive strength of laminated composite plates and stiffened panels is presented. A non-linear finite element code with a new explicit through-thickness integration scheme is proposed for the prediction of the structural responses. A progressive failure analysis is then developed with use of the finite element code coupled with the Tsai—Wu criterion and a limited property degradation model to determine the post-buckling compressive strength of laminated composite plates and stiffened panels. The numerical accuracy and the computational efficiency of the progressive failure analysis were evaluated with reference to the available experimental data, the numerical results of several references, and the analysis with use of the traditional finite element model. A parametric study to investigate the effects of the stacking sequences and the lamina thickness on the post-buckling compressive strength of laminated composite plates and stiffened panels is performed.

A new integrated micro–macro approach to damage and fracture of composites

The element-failure method (EFM) is a novel finite element-based method for the modeling of damage, fracture and delamination in fibre-reinforced composite laminates. The nature of damage in composite laminates is generally diffused and complex, characterized by multiple matrix cracks, fibre pullout, fibre breakage and delaminations. It is usually not possible to model or identify crack tips in the conventional fashion of fracture mechanics. The central idea of the EFM, on the other hand, is to model the damaged portions with partially failed elements, whose nodal forces have been modified to take into account the local damage modes. This has the additional benefit of unconditional computational stability compared to other methods such as material property degradation (MPD) models. Here, we present the application of EFM with a recently-proposed failure criterion called the strain invariant failure theory (SIFT) in the prediction of complex damage progression in open-hole tension (OHT) composite laminates, and show that the damage patterns and predicted final failure loads are in very good agreement with experiments.

Progressive Failure Behaviors of 2D Woven Composites

This paper focuses on understanding the progressive failure behavior of woven composites. Five weaves, i.e. plain, 4-, 5-, 8-harness satin and twill, are considered. Rather than developing a new progressive failure analysis approach, the focus is placed on comparing the damage behaviors of the various weaves predicted by the selected failure criterion and property degradation model. The loading conditions include uniaxial tension and compression. The discussions focus on (1) the effect of the woven architecture on the predicted progressive failure behaviors (2) the similarities and difference in the damage initiation and evolution mechanisms between the plain and satin weaves and (3) the sensitivity of the predicted progressive failure behavior to assumptions about geometric nonlinearity and the property degradation model. The results have shown that the weave architecture (i.e. weave pattern) has significant effects on the predicted progressive failure behaviors even if the composites have the same overall fiber volume fraction, tow waviness and tow cross-section. Comparisons of the damage initiation and evolution mechanisms in the plain and 4-harness satin weaves indicate significant similarities in the damage behaviors in the comparable regions for the two weaves. The results also show that the predicted response of low waviness composite, which is more commonly seen in most structural applications, is quite insensitive to the assumed property degradation model. This imposes difficulties in validating a model by comparison with test results for low waviness composites.

The effects of geometric parameters on the failure strength for pin-loaded multi-directional fiber-glass reinforced epoxy laminate

Abstract A numerical and experimental study was carried out to determine the failure of mechanically fastened fiber-reinforced laminated composite joints. E/glass–epoxy composites were manufactured to fabricate the specimens. Mechanical properties and strengths of the composite were obtained experimentally. Tests have been carried out on single pinned joints in [0/90/0]s and [90/0/90]s laminated composites. A parametric study considering geometries was performed to identify the failure characteristics of the pin-loaded laminated composite. Data obtained from pin-loaded laminate tests were compared with the ones calculated from a finite element model (PDNLPIN computer code). Damage accumulations in the laminates were evaluated by using Hashin's failure criteria combined with the proposed property degradation model. Based on the results, ply orientation and geometries of composites could be crucial for pinned laminated composite joints.

Free Edge Effect on the Post Failure Behavior of Composite Laminates Under Tensile Loading

It is necessary to understand the complete load response and failure mechanism of composite laminates to enhance the full potential of composite materials. Progressive failure algorithm for the post failure behavior of composite laminates was developed in the present study such that the damaged layer with many micro-cracks is replaced with an equivalent layer of degraded properties. Stresses and strains are calculated by the 3-D finite element method based on the generalized layerwise plate theory (GLPT) in order to consider the local effect near the free edges. The types and size of damage in composite laminates are predicted in the failure analysis that consist of a set of failure criteria and property degradation models for each mode of failure. In the case of matrix cracking, the macroscopic stiffness reduction model based on the shear-lag method is introduced to the finite element method in order to consider nonlinear progressive reduction of stiffness at each strain level. In order to predict the failure load and the damage accumulation accurately, the refined finite element model with 3-D stress field is used. The distribution of stress considering free edge effect is presented. The failure mechanism and ultimate failure loads of the cross-ply and quasi-isotropic laminates for different stacking sequences with the same thickness are investigated.