Ductile Damage Research Articles

Low cycle fatigue of components manufactured by rod extrusion: Experiments and modeling

The performance of formed components is significantly influenced by the initiation of ductile damage. Preceding forming operations, for instance, affect the service life determined in fatigue tests. In the current investigation, the effect of ductile damage in forming is isolated by changing the shoulder opening angle in forward rod extrusion. Forming-induced ductile damage is then related to measurements of void area fraction, density and Young’s modulus. Subsequent fatigue tests in the low cycle range indicate that the service life of the extruded components can be improved through a reduction of the forming-induced damage. A novel constitutive model considering forming-induced damage and fatigue damage is proposed to account for the observed behavior in axial fatigue tests of extruded components. The non-local ductile damage formulation is formulated in the framework of Generalized Standard Materials. Kinematic and isotropic hardening are considered. Based on earlier work of Lemaitre and Desmorat, the fatigue damage initiation criterion is extended to take the observed mechanical behavior in low cycle axial fatigue tests of formed components into account. The extended model is able to capture the effect of forming-induced damage on the service life.

Non-linear analysis of eccentric compression of steel and steel fiber reinforced high strength concrete column

To improve the ductility of high-strength concrete and enhance the ductility and load-bearing capacity of steel reinforced high-strength concrete (SRHSC) columns, steel fibers were added to SRHSC to prepare steel and steel fiber reinforced high-strength concrete (SSFRHSC) columns. In order to study the eccentric compression of SSFRHSC columns, based on the experimental study of the eccentric compression of SSFRHSC columns, finite element model specimens of SSFRHSC eccentric columns were established using ABAQUS software, and the accuracy of the model was verified by combining the test results. On the basis of the experiments, the parameters such as steel fiber volume rate, concrete strength and eccentricity distance were further changed to extend the study. The results show that: with the increase of the volume rate of steel fiber from 0.5 % to 3 % and the concrete strength from C40 to C90, the ultimate bearing capacity of the specimen increases by 40.81 % and 58.69 % respectively; at the same time, when the eccentric distance increases from 0 mm to 100 mm, the ultimate bearing capacity of the specimen decreases by 66.76 %, and when the eccentric distance When the eccentricity distance was increased from 0 mm-40 mm to 60 mm-100 mm, the structural damage form changed from brittle damage to ductile damage.

Performance of wildlife fence systems under animal impact load

Wildlife fence protection systems specifically designed for animal protection are critical in mitigating wildlife-vehicle collisions and preserving animal habitats. These systems are quite similar to rockfall barrier systems, which are well studied and developed, however, few studies are specifically oriented toward investigating structural performance of these systems. Despite the similarities, results of studies related to rockfall barriers may not be directly applicable to design and performance evaluation of wildlife barrier systems due to differences in a range of size, shape, and velocity of impactors and structural details. This study aims to bridge this gap by analyzing performance and capacity of wildlife structures in more detail through parametric study with consideration of a wide range of properties and structural details appropriate for these systems, such as mesh type (square and inclined), mesh size, and wire diameters. The behavior of these systems under impact loads is simulated using nonlinear finite element models with consideration of ductile damage and element removal techniques to accurately capture wire rupture and changes in the impactor-fence system interface. The results demonstrate that the response of the system is highly influenced by factors such as mesh type, opening size, wire diameter, and impactor size. Notably, the system utilizing an inclined mesh type exhibits a 35 % higher failure velocity, 50 % greater energy dissipation, and 21 % less maximum displacement compared to the square mesh system. The detailed results and discussions in this study provide valuable insights into the influence of individual parameters on the behavior of wildlife fence systems, aiding in the design of more efficient wildlife barrier systems with enhanced performance.

Experimental study on mechanical properties of locally composite steel and steel fiber reinforced concrete beams

Addressing the construction challenges of steel reinforced concrete structures, steel fibers are employed as replacements for longitudinal rebars and stirrups. Additionally, considering the tensile and compressive properties of steel fiber reinforced concrete, the locally composite steel and steel fiber reinforced concrete (LCSSFRC) structures are proposed. Four-point bending tests were carried out on 18 LCSSFRC beams. Different steel fiber volume fractions (ρsf), specimen lengths (l), concrete cover thicknesses for upper and lower parts of steel compression flanges (Css and Csv), and specifications of shaped steel (Is) were studied. Considering the crack development, bearing capacity, ductility, and final damage pattern, the failure modes of 18 specimens were divided into interface failure, bending-torsion failure, and bending failure. Two types of load deflection curve models were established based on the relationship between failure modes and load deflection curves. Furthermore, the sudden load drop was closely related to the development of bonding cracks. Due to the “bridging effect”, specimens showed increasing trends in bearing capacity and ductility with the increase of ρsf. And it is worth noting that there existed a coupling effect of Csv and l on both the bearing capacity and ductility. Increasing ρsf, Csv, and Is was effective for inhibiting the stiffness degradation.

A novel methodology to characterise the ductile-to-brittle transition behaviour of pipeline steels using the dynamic tensile tear test

Brittle fracture control strategies for high-pressure pipelines are essential to prevent catastrophic failures resulting in significant economic losses and environmental damage. Typically, this is achieved by operating the pipeline well above the ductile-to-brittle transition temperature (DBTT). In general, a series of lab-scale fracture tests, such as the Charpy V-Notch (CVN) or Drop Weight Tear Test (DWTT), are performed at different temperatures to construct the ductile-to-brittle transition curve and determine the DBTT. However, when applied to high-grade steels, correction factors or additional criteria are often necessary to obtain satisfactory results. As an alternative lab-scale testing methodology to characterise high-grade steels, the Dynamic Tensile Tear Test (DT3) has been introduced. Recently, an experimental campaign was conducted with the implementation of a liquid nitrogen spray cooling system to characterise the ductile-to-brittle transition behaviour of X70 grade steel using the DT3 system. In this work, tests were performed at temperatures ranging from −80 °C to 25 °C. The transition behaviour was analysed using measured data, and fractography was performed using Scanning Electron Microscopy (SEM). The DBTT for the considered X70 grade steel was determined, and the performance of the DT3 methodology was compared to CVN and DWTT testing methods. Additionally, numerical models were created using Finite Element (FE) modelling and results were compared to the obtained experimental data. By implementing a stress-strain cleavage criterion in combination with the MBW material model, the models considered both ductile damage and failure, as well as brittle failure and mixed ductile-brittle failure. It can be concluded that the DT3-based transition curve provided a satisfactory DBTT prediction. Furthermore, numerical results showed a good correlation with experimental observations and demonstrated a similar transition behaviour.

Damage Evaluation of T-Stub Connected to Hollow Section Column Using Blind Bolts under Tension

The quantitative calculation and evaluation of seismic damage play a crucial role in ensuring structural safety, conducting performance-based structural analysis, and implementing seismic strengthening measures. However, there is limited research on the damage performance of blind-bolted T-stub steel connections used extensively in prefabricated buildings. In this study, the tensile sub model of a blind-bolted T-stub steel connection in a beam–column joint is investigated. The influence of the flange and web thickness of the T-stub connector, as well as the shear-loaded connecting bolts on the web of the T-stub, on the tensile performance of the sub model are considered. Four tensile destructive tests are conducted on a T-stub connector connected to a hollow section column using blind bolts. The experimental results, including failure modes, force–displacement curves, and strain development in the hollow section column and T-stub, are discussed and analyzed in this study. The test results reveal three main failure modes for this tensile substructure: the plastic deformation of the hollow section column, the bending fracture of the T-stub flange, and the fracture of the T-stub web bolt holes due to compression. Furthermore, a ductile damage finite element analysis method is employed to simulate the fracture damage process of the substructure, and the corresponding damage index is calculated using the typical Park–Ang damage model for evaluation, showing good agreement with the damage classification levels specified in FEMA.

On the predictive capabilities of non‐local models for ductile crack propagation under different levels of stress triaxiality

AbstractDuctile materials are used in many applications such as hydrogen storage and transport, energy plants and additively manufactured components. High safety standards are vital for such applications, which underline the necessity of thoroughly investigating ductile failure to ensure safety and increase components efficiency. Ductile failure is mainly prompted by the evolution of the so‐called ductile damage, characterized by the nucleation, growth and coalescence of microvoids due to plastic deformation. Moreover, the plastic zones formed at the crack tip of ductile materials exhibit high sensitivity to the stress triaxiality level, which in turn distinctly depends on the geometry of the considered component. The quantification of the stress triaxiality at the crack tip is therefore essential to better understand and predict ductile crack propagation and failure. For that reason, a non‐local ductile damage model is employed in this work to simulate the ductile crack propagation under different stress triaxiality conditions. Different geometries are considered, such as constrained geometries of notched bending specimens and unconstrained geometries of center cracked tension specimens, which characterize the different triaxiality levels. To address the effects of thickness and initial crack length, three‐dimensional geometries are simulated, which account for the out‐of‐plane crack‐tip constraints. Finally, to evaluate the prediction quality of the simulations, corresponding experiments have been carried out and direct comparisons are conducted, with respect to the crack length, ductile crack propagation and resistance curves.

Integral-based non-local approach to ductile damage and mixed-mode fracture

The present study focuses on the application of an integral-based approach for constructing non-local ductile damage models. The incorporation of non-locality into the damage accumulation rule enhances the modeling framework and yields simulation results that are physically reasonable, avoiding the issue of pathological mesh-dependence. To achieve a precise depiction of damage accumulation and fracture under mixed-mode I/II loading, novel delocalization kernels are proposed. These kernels explicitly consider the heterogeneity of stresses and strains in the fracture process zone; the new kernels are categorized into stress-based and strain-based families. Furthermore, rigorous receiver-based normalization procedures and physically meaningful source-based normalizations are explored for the developed kernels. The outcome of this study is the modeling tool, suitable for end-to-end simulations of damage accumulation and fracture. Using a well-calibrated material model, the practical applicability of the new approach is demonstrated by performing finite element analysis on fracture tests conducted on compact tension–shear specimens. In contrast to the conventional delocalization kernels, the newly introduced families of kernels offer an additional fitting parameter, valuable in accurately describing the structural behavior under mixed-mode loading conditions. In particular, the proposed approach enables control over the shape of the predicted KIc–KIIc diagram.

Characterisation of strength and deformation characteristics of alkali-activated rice husk ash filler-assemblage perimeter rock

In this study, the strength characteristics, deformation characteristics and damage characteristics of three kinds of specimens, namely, surrounding rock, cemented paste backfill (CPB) and a surrounding rock-CPB combination, were studied by uniaxial compression testing using rice husk ash and slag as cementing materials, and the mechanical properties of the combination specimens with different height ratios were also analyzed. The results showed that the surrounding rock specimens were the strongest, followed by the composite body, and the CPB was the weakest. The relationship between different height ratios of the assemblage and the cut line modulus was found according to the fitted curves. The CPB specimens and the surrounding rock specimens showed ductile damage, while the assemblage specimens showed brittle damage.

A numerical ballistic performance investigation of Armox 500T steel through ductile damage models

In this work, the ballistic response of an armor steel, Armox 500T, is numerically investigated through finite element (FE) analysis by utilizing the Johnson–Cook (JC) and modified Mohr–Coulomb (MMC) damage models, with a focus on emphasizing the consequences of different modeling approaches. Although Lode-dependent failure models are considered to increase the accuracy of numerical predictions for ductile failure, there remains a complete lack of clarity as to whether all conditions and materials necessitate the adoption of such models for ballistic impact simulations. In this context, MMC and JC model parameters are calibrated through tensile test data available in the literature enabling direct comparison between them. Damage models are then validated using ballistic impact tests of Armox 500T performed with 7.62 API projectiles. The results indicate that the MMC model outperforms the JC model at predicting the failure modes while both models demonstrate strong performance in anticipating the residual velocity. The influence of projectile nose shape, target plate thickness, and impact angle are further investigated, and the effect of incorporating the Lode parameter is discussed in detail. Impact simulations with the blunt projectile nose shape is found to be highly sensitive to the effect of Lode angle on failure, with differences of up to 20% between models, while 7.62 API shows the lowest sensitivity. The difference between the models’ predictions is observed to increase at lower impact velocities and higher impact angles demonstrating the necessity of a Lode-dependent failure model for such cases. The JC model consistently yields smaller residual velocities compared to the MMC model in all cases indicating that the MMC is more conservative in terms of predicting protective performance of Armox 500T.

Prediction of FLD using Abaqus and Gurson Model for Simple Flat Spacemen

In the past century, in many industries, such as, metal forming industry, it has been important to predict ductile damage and fracture of metals under complex loadings. Regarding damage mechanics, one of the most classical models is the GTN, which was originated from Gurson and later enhanced by Tvergaard and Needleman. The inprovement was achieved by introducing an equivalent void volume fraction f and two more parameters called q1 and q2 into the yield function of Gurson’s model.

From ductile damage to unilateral contact via a point-wise implicit discontinuity

Ductile damage models and cohesive laws incorporate the material plasticity entailing the growth of irrecoverable deformations even after complete failure. This unrealistic growth remains concealed until the unilateral effects arising from the crack closure emerge. We address this issue by proposing a new strategy to cope with the entire process of failure, from the very inception in the form of diffuse damage to the final stage, i.e. the emergence of sharp cracks. To this end, we introduce a new strain field, termed discontinuity strain, to the conventional additive strain decomposition to account for discontinuities in a continuous sense so that the standard principle of virtual work applies. We treat this strain field similar to a strong discontinuity, yet without introducing new kinematic variables and nonlinear boundary conditions. In this paper, we demonstrate the effectiveness of this new strategy at a simple ductile damage constitutive model. The model uses a scalar damage index to control the degradation process. The discontinuity strain field is injected into the strain decomposition if this damage index exceeds a certain threshold. The threshold corresponds to the limit at which the induced imperfections merge and form a discrete crack. With three-point bending tests under pure mode I and mixed-mode conditions, we demonstrate that this augmentation does not show the early crack closure artifact which is wrongly predicted by plastic damage formulations at load reversal. We also use the concrete damaged plasticity model provided in Abaqus commercial finite element program for our comparison. Lastly, a high-intensity low-cycle fatigue test demonstrates the unilateral effects resulting from the complete closure of the induced crack.

Low velocity impact tube hydroforming process: experiments and FSI modeling by considering ductile damage model

Low velocity impact tube hydroforming process: experiments and FSI modeling by considering ductile damage model

Characterization of ductile damage and fracture behavior under shear reverse loading conditions

AbstractThis paper deals with experimental and numerical analysis of the ductile damage and fracture behavior undergoing biaxial non‐proportional shear reverse loading conditions. In the numerical analysis, an anisotropic cyclic plastic‐damage constitutive model is considered to characterize the damage and fracture behavior. Additionally, the change in the hardening rate is observed after shear reverse loading. Thus, a newly modified non‐hardening strain region method is introduced to capture the change in the hardening ratio between isotropic and kinematic hardening. Furthermore, the damage surface is assumed to translate in the direction of the damage strain increment. Hence, a softening law based on the damage strain is proposed. The modified constitutive model predicts macroscopic force‐displacement and microscopic evolution of plastic and damage behaviors under shear reverse loading with a tensile preload. Through digital image correlation technique and scanning electron microscopy, numerical results can be validated by experimental ones. Furthermore, scanning electron microscopy pictures also reveal different damage and fracture mechanisms on the micro‐level.

Composition-dependent transformation-induced plasticity in Co-based complex concentrated alloys

While the mechanically-induced martensitic transformation and transformation-induced plasticity (TRIP) effects have various known benefits, transformation of blocky martensite can also accelerate ductile damage nucleation and growth. Some complex-concentrated alloys (CCAs) with negative stacking-fault energy (SFE) demonstrate a rare faulting plasticity behavior with high strain hardening capability, that sets them apart from conventional low, positive SFE alloys that exhibit the TRIP effect. This study investigates the influence of dilute nitrogen on the TRIP mechanisms in a Co-rich CoCrNi CCA, and reveals, among other findings, that nitrogen interstitials can effectively reduce the extension of stacking faults and deformation-induced phase transformation, resulting in higher strain hardenability at early deformation levels and ductility. Thermodynamic calculations are coupled to various experimental analyses based on atom-probe tomography, scanning transmission electron microscopy, electron backscattered diffraction, electron-channeling contrast imaging, in situ high-energy synchrotron X-ray diffraction, and stress relaxation testing, to explore the origins of the observation. This work provides insights into the future design of CCAs with desirable TRIP, faulting plasticity, and mechanical properties.

Effect of Planting Rebars on the Shear Strength of Interface between Full Lightweight Ceramsite Concrete and Ordinary Concrete

The use of full lightweight ceramsite concrete (FLWCC) for the repair of ordinary concrete (OC) structures has a good application prospect in the field of engineering structural strengthening. However, the interface here is less studied at present. For this purpose, 10 sets of FLWCC (new concrete)–OC (old concrete) specimens were produced for the shear test to test the bonding properties of the interface. The results showed that the damage form was changed from brittle damage to ductile damage after strengthening. It was proven that planting rebars in the interface could improve the shear performance. The interface shear strength increased with the number of rebars and it had a better effect after the number was more than 2. The strength was related to the rebar diameter and the maximum was obtained when the diameter was 8 mm. The most suitable spacing of the bars was 80 mm. The one-way analysis of variance (ANOVA) showed that the number of rebars had the greatest effect on shear strength followed by rebar diameter, while the effect of the spacing of the bars was less pronounced. Moreover, Fib’s (2010) specification of the interface shear strength formula could be used for the calculation of FLWCC–OC.

Ductile damage and failure of thin sheet metals: New biaxial experiments and numerical simulations

AbstractThe paper deals with the ductile damage and failure behavior of thin sheet metals under proportional biaxial loading paths. A newly designed specimen is presented and an experimental series with different loading ratios is performed. Corresponding numerical simulations including plastic anisotropy reflect the stress state and enable the interpretation of the different damage mechanisms. Due to fabrication issues the specimen geometry for this class of materials has to get by without notches in thickness direction and consequently the new specimens pre‐define the localization by a series of holes. The strain fields at the specimen surface are evaluated by digital image correlation and the fracture surface is analyzed by scanning electron microscopy. The experimental and numerical methods described here provide a possibility for the targeted investigation of the ductile damage behavior of thin sheet metals under proportional loading.

Calibration of ductile and shear damage models for carbon and stainless steel shear studs

AbstractSteel‐concrete composite beams are commonly used in bridge construction. The corrosion of the supporting steel beams and the shear connectors are however known as a major cause of premature deterioration of composite bridges. Stainless steel beams and shear connectors offer a viable alternative solution to the steel corrosion problem in composite bridges located in harsh environmental conditions. This paper presents experimental and numerical investigations of the tensile and shear behaviour of stainless steel welded shear connectors. The results of tensile coupon and double shear tests on stainless steel and carbon steel shear connectors to characterise the tensile and shear response are reported. Numerical modelling is carried out using the ABAQUS finite element software to develop calibrated ductile damage and shear damage fracture models for stainless steel shear connectors. The development and validation of the numerical models together with the calibration of the fracture models are presented and comparisons are made with those of carbon steel shear connectors.

Inter-void shearing effect on damage evolution under plane strain deformation in high-strength aluminum alloy sheet

In this study, the ductile damage responses of high-strength 7000 series aluminum alloy (AA), AA 7075-T6 sheet samples, subjected to the plane strain deformation mode were investigated using finite element (FE) simulations. In the experiments, uniaxial tension (UT) and plane strain tension (PST) tests were conducted to characterize the plasticity and ductile damage behavior of the AA 7075-T6 sheet samples. The limiting dome height (LDH) and V-die air bending tests were conducted to evaluate the ductility of the material subjected to plastic deformation and friction between the tools, and the corresponding fractured samples were qualitatively analyzed in terms of dimples using fractography. FE simulations were performed to predict the ductility of the AA 7075-T6 sheet samples under plane strain deformation using an enhanced Gurson−Tvergaard−Needleman (GTN) model, namely the GTN-shear model. The model was improved by adding the shear dimple effect to the original GTN model. The predicted results in terms of the load–displacement curves and displacements at the onset of failure were in good agreement with experimental data from the aforementioned tests. Furthermore, virtual roll forming simulations were conducted using the GTN-shear model to determine the effect of the prediction on ductile behavior for industrial applications.

Influence of stem design parameters on periprosthetic femoral fractures examined by subject specific finite element analyses.

Due to the increasing number of periprosthetic femoral fractures (PFF), the optimisation of implant design gains importance. For the presented research a validated, subject specific finite element model of a human femur with an inlying total hip stem was used to compare the influence of different geometrical implant parameters on the development of PFF. The heterogeneous bone tissue was modelled on the basis of computed tomography scans. A ductile damage model with element deletion was applied to simulate bone fracture in a load case re-enacting a stumbling scenario. The results were compared in terms of fracture load, subsidence and fracture pattern to analyse the influence of friction at the implant-bone interface, implant size and stem length. The results showed that higher friction coefficients lead to an increase of fracture load. Also, the usage of an oversized implant has a negligible effect while an undersized implant reduces the fracture load by 48.9% for the investigated femur. Lastly, a higher fracture load was reached with an elongated stem, but the bending and change in fracture path indicate a more distal force transmission and subsequent stress shielding in the proximal femur.