Failure Behavior Of Materials Research Articles

Anisotropic damage evolution in solid fractures: A novel phase field approach with multiple failure criteria and directional-dependent structural tensor

This study proposes a novel phase-field fracture model based on unified phase field theory, aiming to overcome current limitations in simulating material complex fracture behaviors. Through this model, analytical solutions for two-dimensional bars subjected to tensile or compressive stresses are provided, enabling the coupling of multiple failure criteria and further proficient simulation of mode-I, mode-II, and mixed mode-I/II fractures, effectively addressing challenges faced in modelling materials with different or complex failure modes under various loading conditions. Furthermore, to account for the strong anisotropic failure behavior of materials, a novel directional-dependent structural tensor is proposed. The tensor correlates fracture energy with crack surface orientation, facilitating precise characterization of material damage evolution with multiple potential crack orientations. This tensor ensures the consistency of phase-field fracture evolution with predefined fracture patterns. The effectiveness of the proposed model is validated through case studies, emphasizing its robustness and superior predictive capability in capturing fracture behavior under various conditions. This research provides a more accurate and universally applicable approach for simulating material failure, particularly for complex or multiple failure mode material failure simulations.

A three-dimensional failure criterion model considering the effects of fiber misalignment on longitudinal tensile failure

This paper proposes a three-dimensional failure criterion model for unidirectional fiber-reinforced composites. In contrast to previous models that only accounted for the effect of fiber misalignment in the presence of longitudinal compressive stress, the proposed failure criterion model comprehensively considers the effect of localized misaligned regions on the failure under any stress state. Another key contribution of this study is the introduction of the effective misalignment angle. Considering effective misalignment angles, the proposed failure criterion model can reasonably reveal the effect of localized misaligned regions on the failure behavior under different stress states. The agreement between the predicted results and the experimental data proves that the proposed model has good applicability. Furthermore, the influence of initial misalignment angles on failure is analyzed under varying stress conditions. The results indicate that even under longitudinal tensile stress, the initial misalignment angle still plays an important role in the failure behavior of materials.

Unraveling kinking: A plasticity enhancing failure mode in high strength nano metallic laminates

Kinking is an important and plasticity-enhancing deformation/failure mode in numerous mechanically anisotropic materials including high-strength nano metallic laminates (NMLs). However, our current limited understanding of the mechanics of kinking and its dependence on microstructural attributes is insufficient for thoroughly comprehending and eventually being able to control failure behaviors of materials. In this study, we investigate kinking dependencies on microstructural attributes in NMLs via in situ micropillar compression, multiscale microstructure characterization, dislocation dynamic simulations, and crystal plasticity modeling. By examining several NML systems (Cu/Fe, Ag/Fe, Al-4Mg/Fe), we demonstrate that the development of internal stresses during loading activates local layer-parallel glide triggering kinking in NMLs. Furthermore, this work reveals the effect of key microstructural features including layer thickness, layer waviness, interface barrier strength, and work hardening capacity on kink band formation in NMLs. More broadly, our efforts represent a generically applicable approach for probing large-strain deformation behavior of complex materials via synergetic modeling and experimental efforts.

Investigation of the Damage Phenomenology with Dependence on the Macroporosity and Microporosity of Porous Freeze Foams

Freeze Foams are cellular, ceramic structures with hierarchical pore structures that are manufactured using the direct foaming process. By tailoring their morphology and strength, these foam structures are able to cover a wide range of application. Earlier works identified that pore-forming influencing factors (water and air content, suspension temperature, as well as pressure reduction rate) dictate the constitution on a macroscopic and microscopic scale. Therefore, the ability to manufacture foams whose properties align with the component requirements would be an important step in advancing towards a widespread application of these promising materials. With this goal in mind, the correlation between the pore-forming influencing factors and the resulting mechanical properties was quantified. Foams with independently adjustable porosities were produced at the micro and macro scales and evaluated according to their material failure behavior under compressive loads. As a result, foams with determined macroporosities between 38 and 62%, microporosities between 25 and 42%, and compression strengths between 1 and 7 MPa with different material failure characteristics were manufactured and systematically investigated.

Modelling of Failure Behaviour of 3D-Printed Composite Parts

Failure in 3D-printed composite parts is complex due to anisotropic properties, which are mainly governed by printing parameters, printing strategy, and materials. Understanding the failure behaviour of materials is crucial for the design calculations of parts. Effective computational methodologies are yet not available for accurately capturing the failure behaviour of 3D-printed parts. Therefore, we proposed two different computational methodologies for modelling the failure behaviour of 3D-printed parts. 3D-printed parts subjected to uniaxial tensile loading were considered for modelling. In the first method, the computational model employed nonlinear properties of virgin material, and the model predicted higher values than the experimental results. This method provided idealistic nonlinear behaviour of 3D-printed parts. The difference in the results of experimental and computational is significant, especially in the case of 3D-printed composites. In the second method, the computational model utilized nonlinear material data from mechanical testing results and the model predicted accurate nonlinear behaviour of 3D-printed parts. This method provided realistic material behaviour of 3D-printed parts. Therefore, for effective design and analysis, it is suggested to use the latter computational methodology to capture the failure behaviour of 3D-printed parts accurately.

Mechanism in damage variation of nanosecond laser-induced damage of germanium sheets in vacuum

Laser-induced damage of germanium (Ge) sheets plays a key role to estimate the lifetime of optical components in the vacuum and space irradiation environment. However, the dependence between the degrees of laser-induced surface damage and nanosecond pulsed irradiation remains unclear for Ge sheet. Here, we investigate damage morphology and the growth characteristic of Ge sheets under different conditions and measure the laser-induced damage threshold (LIDT) in vacuum. Our results reveal that optical reflectivity of Ge in vacuum chamber falls 92% because of the defective sites on the damaged surface. The area, the depth and the size of the damage crater increase but the hillock height and the surrounding thermal diffuse area decrease along with the increase of vacuum degree. The thermal effect, the failure effect of plasma shock wave and the mechanical stress are analyzed to be the main mechanism in the laser damage. The combined experimental and theoretical work gives an insight into the change of surface damage and material failure behavior, hence broadens the potential applications of Ge sheets in areas of laser material manufacturing and laser processing.

On-Chip Generation Method of Shock Load and Characterization of Microstructure Shock Process

Different from the device-level research on MEMS shock reliability, this paper introduces an on-chip generation method of shock load, which realizes the in-situ shock test directly loaded on the microstructure. To achieve energy storage and rapid release, a crossbow-type shock load generating structure that can integrate the test sample is proposed. The shock behavior is characterized by the high-speed camera, and the simulation model is established by the finite element software LS-DYNA. Under the shock acceleration of more than 100,000 g, the high-speed switching waveform generated by the microscale mechanical shock was observed with an oscilloscope for the first time. And the shock contact process and the dynamic fracture process of single-crystal silicon (SCS) structures in less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\mu \text{s}$ </tex-math></inline-formula> were exhibited. This work has the potential to be used to evaluate the shock resistance reliability of MEMS microstructures in mechanical shock environments, as well as to study material dynamic properties and material failure behaviors at the microscale. [2022-0076]

A comparative study on the effect of nano seashell, multiwall carbon nanotubes and nano alumina on mechanical and impact properties of bidirectional Kevlar/epoxy composite

The use of composite materials is becoming more widespread by the day. Composite materials are used in a variety of vital applications including aerospace, defense and marine. As a result, it is critical to investigate the mechanical and impact properties of these material-based components. Testing of these materials can provide information such as Ultimate Tensile Strength, Impact Strength, and modulus of elastic allowing their application to be better understood. It has been observed that symmetric laminates produce better results. Because of the presence of stiff filler material, the infusion of nanofillers changed the material failure behavior from ductile to brittle. In this comparative study, an attempt has been made in investigating the improvements in the material behavior of neat Kevlar along with the infusion of nano additives like alumina, seashell and MWCNT in varying proportions. Based on the obtained experimental values, graphs were plotted to demonstrate the variation of properties when these infusions were made. There is a significant improvement in the modulus values of the material, Ultimate tensile strength and Impact strength after the incorporation of the nano additives. The Ultimate Tensile Strength was improved by 0.32% in Alumina 1% + 0.25% wt. MWCNT, 21% improvement was found in Alumina 3% + 0.25% wt. MWCNT and 28.86% improvement in alumina 6 % + 0.25% wt. MWCNT compared to neat aramid fiber composite specimen. For the combination of seashell + MWCNT, it is also found that Ultimate Tensile Strength is considerably improved. It was observed that, that there is a 15.96% improvement in Seashell 1% + 0.25% wt. MWCN, 21% improvement in Seashell 3% + 0.25% wt. MWCNT and 29.78% improvement in Seashell 7% + 0.25% wt. MWCNT compared to neat aramid fiber composite specimen. The impact strength was evaluated by performing Charpy Impact Test (ASTMD 256). It was found that there is a 12% improvement in Seashell 1% + 0.25% wt. MWCNT, for Seashell 2% + 0.25% wt. MWCNT, there is a 50% increment in the Impact Strength value. It is also seen that impact properties have significantly improved when the combination of Alumina + MWCNT was infused. There is a 23.072% rise in Alumina 1% + 0.25% wt. MWCNT and 56.83% improvement in Alumina 3% + 0.25% wt. MWCNT compared to its neat aramid fiber composite specimen.

Experimental prediction of lead failure under tensile load using scanning contact potentiometry technique

The issue of accurate identifying in advance structural nonhomogeneities of metals is one of the main factors in improving the manufacturing efficiency and safety during service. This paper illustrates the conventional uni-axial tensile test that is carried out on the diffuse and localized necking stages of dog-bone shape lead specimen. The scanning contact potentiometry method was used to locate the rupture zone. Infrared radiation was used to heat the specimen up to 40°C, in order to excite structural nonhomogeneities in the bulk of the tested specimen. It was found that the infrared radiation increases the predictable nonhomogeneity zone. A ductile rupture occurs in the same nonhomogeneity zone that was previously exactly identified using the scanning contact potentiometry method. The formed diffused necking was observed to initiate from the right where the rupture spread diagonally, at an angle of 70° between the tensile axis and the rupture plane. However, the angle between the tensile axis and the hexagonal singular reflex plane was 69°, which was slightly different from the rupture angle. Both results of the rupture angles of the tensile test and the SCP are relatively matching and diverse from the theoretical calculations. The results shown in this work highlight the importance and the efficiency of the experimental SCP method in prediction of the material failure behaviour.

Reliability analysis of truss structures considering complete failure paths and using the FLHB model

abstract: The study of progressive collapse of structures using numerical models requires accurate modeling of geometrical nonlinearity and material failure behavior. Numerical models must demonstrate stability, such that localized member failures do not trigger numerical instabilities. Also, algorithms should be efficient, to limit the computational burden of analyzing multiple responses when considering the effects of uncertain loads, geometric and material variables. In this scientific domain, a comprehensive non-linear ductile-damage truss-element model has been recently presented by the authors. The model accounts for the geometrical and material nonlinearities observed during progressive collapse of structural systems. In this paper, the Felipe-Leonel-Haach-Beck (FLHB) model is calibrated to describe the response of Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC). Based on a limited number of UHPFRC experimental curves, statistics of FLHB model parameters are obtained. These are employed in the probabilistic analysis of failure paths of truss structures under progressive collapse. Monte Carlo Simulation and the First Order Reliability Method are employed in the probabilistic failure path analyses. Six application examples demonstrate the accuracy, robustness, and efficiency of the FLHB model in evaluation of failure paths of realistic structural systems.

Structural failure criterion for spatially-reinforced carbon-carbon composite materials

This paper defines the structural strength criterion for 4DL-reinforced carbon-carbon materials. For this scheme, fiber reinforcement consists of four groups of reinforcing elements, three of them are located in parallel planes with the angles of 120° between them and the fourth one is normal to them. The paper addresses the first failure of the material corresponding to its yield stress, in this point, one of the material components deviates from linear elastic behavior. A composite material is considered to be non-uniform structurally and consists of a matrix and reinforcing elements, rods. Those rods, in their turn, represent a unidirectional composite. To analyze the stress-strain state of individual components of the material, a three-level elastic model is built that uses the analytic approach at the micro level, while at higher levels it uses the finite element method. For numerical calculations, a structural cell of the material is taken. The boundary conditions provide small to negligible influence of the edge effects, thus simulating the behavior of the infinite volume of the material. For the material components, local strength criteria are introduced, where the fields of the criterion quantities are averaged over the volume of the structural cell. The strength surface of the material that corresponds to its first failure is obtained, and the conclusion is made that the suggested criterion provides a reasonable agreement with the available data on the typical carbon-carbon composite characteristics. Based on the calculated dependencies of the material’s yield stress on the load direction, a procedure is suggested to identify the model parameters based on the material failure behavior analysis using standard tensile and compressive tests. Estimated discrepancies between the results calculated using the suggested criterion and those obtained using the limiting stress criterion for biaxial stress states are given. It is shown that the discrepancy may reach tens of percent and in some cases the material strength increases in comparison with that in the uniaxial stress state. The results are subject to verification tests in order to verify the model for advanced spatially reinforced carbon-carbon composite materials.

Critical ductile fracture criterion based on first principal stress and stress triaxiality

A series of quasi-static fracture tests on ten types of specimens for six types of materials were performed to investigate the ductile fracture failure behavior of materials. The full-range equivalent stress-strain relations of materials were obtained by using finite-element-analysis aided testing method. The critical failure behavior was discussed in detail by the analysis of the local stress and strain distributions on the cross-sections of specimens and fractographic observation of specimens. The results show that the first principal stress is the dominant factor of ductile fracture failure. A novel critical fracture criterion of ductile materials represented by the critical first principal stress and critical stress triaxiality is proposed, and the validity of the proposed criterion has been successfully examined.

Finite element analysis of synergetic deformation in precision cutting of polymer bonded explosive

Synergetic deformation behavior between crystal particles and polymeric binders dominates the machinability of energetic materials. In the present work, we elucidate cutting mechanisms of HMX-based polymer bonded explosive (PBX) in orthogonal cutting by numerical simulations based on a cohesive finite element framework. The polygonal HMX crystals with a particle volume fraction of 90% are modeled by a linear elasticity model, while the HTPB binders are described by a rate-independent hyperelastic model coupled with a rate-dependent plasticity model. Furthermore, cohesive elements are implemented in both crystal particles and binders to describe thermal-mechanical coupling-induced material failure behavior in the cutting process of PBX. Simulation results reveal different deformation modes of PBX, as well as their correlations with machining results. Furthermore, it is found that depth of cut has a strong impact on the cutting processes of PBX, in terms of material failure mode, subsurface damage and energy dissipation. These findings provide important guidelines for the design and synthesis of energetic materials with high machinability.

A comparison of stress triaxiality and strain distributions in notched bar geometries as determined by Bridgman expressions and finite element analysis

When characterising the failure behaviour of materials, it is often necessary to construct a ductile failure locus which relates the strain at failure to the level of stress triaxiality exhibited. The data required for a locus can be determined through multiaxial tensile testing of notched bars, using a range of notch radii to produce different levels of triaxiality. The triaxiality and strain values may be calculated using expressions derived by Bridgman, which only require knowledge of the cross-sectional radius and edge profile radius of curvature. However, the validity of such expressions may not extend to sharp notches. Experimental testing of notch bars was performed, and specimen profiles measured through image capture for the duration of the tests. These data were processed and triaxiality and strain values were calculated using the Bridgman expressions. Finite element analyses were performed to simulate the test specimen geometries, and results for the triaxiality and strain were compared to Bridgman’s estimates. Very poor agreement was found between the two methods of determining the triaxiality values, and Bridgman’s assumption that the strain is uniform across the radius of the specimen was found invalid under these conditions. It is thought this is likely due to the fact Bridgman’s analysis was for specimens that were initially smooth and formed a neck at high strains, as opposed to specimens that are initially notched. These findings suggest that it is not accurate to use the Bridgman expressions to formulate a failure locus for tensile notch bar tests, and it is instead recommended that the finite element analysis is employed for these purposes.

Perspective on the mechanical response of pineapple leaf filler/toughened epoxy composites under diverse constraints

In view of fiber orientation problem and seminal ecological economics, the present research work is concentrated on the development of ‘commercial adhesive grade’ epoxy composite reinforced with surface-modified low-cost ‘agronomic waste’- based pineapple leaf (PALF) fillers. To overcome the potential adhesion and moisture absorption issues, surface modification of fillers is accomplished with alkaline treatment. The change occurred in the crystal structure and thermal stability of fillers before and after the treatment is quantified using X-ray diffraction and thermogravimetric analysis. The composite samples are subjected to the tensile test with varying strain rate to investigate its effect on the tensile properties and failure behavior of materials. In addition to this, the plane-strain fracture toughness and flexural test have also been carried out to evaluate the composite properties in bending mode with and without the preexisted crack in materials. The dynamic mechanical analysis has also been conducted from room temperature to 150 °C to evaluate the temperature dependence of mechanical properties. The crystallinity of treated filler has been improved by 8 % due to the loss of non-cellulosic components from filler molecules. The highest value of ultimate tensile strength and Young’s modulus are 22 MPa and 570 MPa, respectively. The maximum values of storage modulus of 10 GPa and glass transition temperature of 91 °C were observed for 2.5 % and 12.5 % of filler content, respectively. From these findings, it is envisaged that the balanced tensile and dynamic mechanical properties of PALF–epoxy composites will elucidate their potential applications.

Optimization on strength spot welding joint trough finite element modelling indentation approach

Failure behaviour of spot welding are important in order to design the weld strength on dissimilar spot welded joint as a significant step to reduce vehicle weight in the development of urban transportation systems. Environmental friendly. Including in this case to take positive measures to reduce CO2 emissions and reduce fuel consumption. The material failure behaviour, properties parameter of plastics materials and fracture of materials can be easily determined when the specimen material standards (i.e parent metal) but for the results of spot welding joint testing standards are not applicable to characterize the HAZ and spot welding nugget because it is constrained by a complex structure and a small sample size. One potential approach to be developed in the behaviour of material failure, parameter plastic properties of material is to combine the numerical-experimental method. Where ph-curve indentation experimental results combined with numerical approach through Finite Element (FE) modelling. Approach was established to be used for reverse (inverse) testing of the nature of constitutive material (i.e the yield stress (σy), the coefficient of strain hardening (n)) for nugget, HAZ and the parent material (base). In this approach the Load data of material deformation used as input data for finite element model (FE) which simulates the geometry and boundary conditions of the experiment. Finite element model (FE) Model-based approaches are developed, validated then used to predict the effect of nugget size and thickness of the sheet metal on the strength of the weld joint points with different materials (dissimilar material).

Multifield modelling and failure prediction of cellular cores produced by selective laser melting

AbstractA multifield simulation approach of cellular cores produced by additive manufacturing is presented. The analysis is aiming to derive the relation between the manufacturing process parameters and the resulting material failure behaviour. To this purpose, the selective laser melting manufacturing process is initially thermo‐mechanically simulated, followed by the mechanical analysis of the nonlinear core behaviour. The methodology is demonstrated in the case of open‐lattice body‐centred‐cubic (BCC) cellular cores.

Nanosecond laser-induced surface damage and material failure mechanism of single crystal CaF2 (111) at 355 nm

Surface damage and material failure mechanism of CaF2 single crystal by 355 nm/6.8 ns laser pulses are systematically studied in this work. Surface damage characteristics, such as damage threshold, damage growth threshold, damage growth laws and damage growth coefficient of CaF2 crystal are carefully studied. Surface material cracking and local material vitrification (from CaF2 crystal to defective CaF2-x materials) are revealed. Material decomposition, oxidation and formation of Ca0, Ca2+and (F−-F−) centers in surface layer are illustrated. Laser-driven thermal accumulation and thermal-stress gradient in CaF2 crystal are calculated and discussed based on the theory of Fourier heat conduction and thermal-elastic constitutive equations. Theory analysis suggests that the material failure process in CaF2 crystal is mainly driven by significant thermal stress gradient. Thermal gradient induce the material decomposition and local vitrification in CaF2 crystal. Combined results on surface damage and material failure behavior are beneficial to understand nanosecond laser-driven modifications and damage in fluoride crystals at ultraviolet wavelength.

High Rate Compressive Behaviour of a Dilatant Polymeric Foam

Polymeric foams are an essential part of personal protection equipment, such as helmets and body armor. In this work, the authors study the strain-rate dependent behavior of a dilatant polymeric foam, focusing on developing characterization and testing methodologies needed to better understand the links between microstructure and failure in these materials. The authors study these links for a commercially-available shear-thickening foam, named D3O LITE D. Prior to testing, the pore sizes (82 ± 26 µm), ligament thickness between pores (5–12 µm), and porosity (83 ± 5%) were quantified using scanning electron microscope images. Samples were then tested in compression under quasi-static conditions for a strain rate of 0.04 s−1 using an MTS testing apparatus, and in dynamic conditions using a split Hopkinson pressure bar apparatus for strain rates of 5280–5720 s−1. For both rates, strains upwards of 85% were achieved and this allowed us to examine a variety of material failure behaviors, including elastic collapse, localization, pore collapse, densification and post pore collapse hardening. These mechanisms are observed in-situ during compression experiments using high-speed photography, and linked back to stress–strain responses of the materials. In this material, the elastic collapse stress for quasi-static and dynamic compression conditions was found to be 120 ± 40 kPa and 243 ± 47 kPa, respectively, and elastic modulus were noted of 2.4 ± 0.7 MPa and 3.8 ± 1.2 MPa, respectively. Following the elastic collapse, some unique specimen-scale localization features were observed during the dynamic experiments. These features are unique to dynamic compression and were not observed for the quasi-static case, demonstrating a demonstrating a distinct high-rate behavior for this material, possibly linked to its “shear thickening” label. After densification, complete pore collapse followed by post pore collapse hardening were observed for both strain rates. These results represent some of the first studies on shear-thickening foams in the literature, and the testing methodologies developed in this study will serve as the foundation for additional experimental and computation studies across a broader range of foam materials.

Evaluation of the ductile fracture of Q460 steel under two different failure criteria

The evaluation and the prediction of the failure behaviour of materials are fundamental in improving the design and the service life of components/structures. Recent studies in continuum mechanics have pointed out that the ductile damage evolution is influenced by two parameters: the stress triaxiality and the Lode angle.In the present work, a coupled elastoplastic and damage constitutive model was adopted for the evaluation of the failure behaviour of Q460 steel under monotonic loading. Two different failure criteria, the modified Mohr-Coulomb (Bai and Wierzbicki, 2010) and modified Lemaitre’s criteria (Lemaitre, 1985a), were compared for the description of the crack formation in tensile tests for round notched bars and flat grooved plates. The two different types of geometry are functional to highlight the role of the Lode angle parameters in the ductile fracture. In the same way, the different radii of the notches and grooves are responsible for lower or higher levels of stress triaxiality, affecting the material ductility. The numerical analyses were compared with the experimental and numerical work carried out by Li et al. (2016) proving the reliability of the numerical model.