Elastic-plastic Fracture Mechanics Research Articles

Effect of Laser Power on the Microstructure and Fracture of Notched IN718 Specimens Fabricated by Laser Powder Bed Fusion

This study examines the impact of laser power on the microstructure and fracture behavior of IN718 specimens fabricated using laser powder bed fusion. Single-edge notched bend specimens were fabricated with varying laser power from 140 W to 260 W, and their fracture behavior was analyzed following the ASTM E1820-23b standard. The porosity and grain morphology remained unaffected by the presence of a notch parallel to the build direction. An elastic–plastic fracture mechanics approach was used to measure J-R curves, which quantify the energy required for crack propagation. Crack initiation and growth during quasistatic loading were monitored using image analysis. The results revealed a strong correlation between crack initiation and propagation, type of porosity, and relative density. The specimen printed with the optimal laser power of 180 W demonstrated the highest relative density and the greatest resistance to crack propagation. Large non-spherical defects formed due to lack-of-fusion at lower laser power are more detrimental to the crack propagation resistance.

Engineering definition of small scale yielding condition using imaginary crack tip opening displacement: A practical approach of elastic-plastic fracture mechanics

Engineering definition of small scale yielding condition using imaginary crack tip opening displacement: A practical approach of elastic-plastic fracture mechanics

A plastic analysis of Griffith crack problem in 1D hexagonal piezoelectric quasicrystals

The elastic–plastic fracture mechanics of one-dimensional (1D) hexagonal piezoelectric quasicrystals (QCs) Griffith crack under a small-scale yielding is studied. Due to the properties of this material, the atomic cohesive force zone of the phonon field is the smallest. Based on the theory of distributed dislocation, the mechanical and electrice coupling model for the elastic–plastic fracture mechanics of 1D hexagonal piezoelectric QCs Griffith crack under a small yield range is established for the first time. The crack opening is arrested by prescribing the cohesive loads of yield point phonon field, phason field and electric field over the phonon field atomic cohesive force zone, the phason field atomic cohesive force zone and saturation zone rims, respectively. Without loss of generality, two cases are considered. Using Dugdale method, the corresponding size of atomic cohesive force zone is obtained. By using Fourier transform and the integral equation method, the closed analytical expressions of phonon field crack opening displacement (COD), phason field COD, crack opening potential drop (COP) and J-integral are obtained. Numerical analysis results show that crack arrest is possible in 1D hexagonal piezoelectric QCs under small-scale yielding, which provides a theoretical basis for the application of QCs materials.

Chemical Equilibrium Fracture Mechanics—Hydrogen Embrittlement Application

Chemical Equilibrium Fracture Mechanics (CEFM) studies the effect of chemical reactions and phase transformations on crack-tip fields and material fracture toughness under chemical equilibrium. An important CEFM direction is hydrogen-induced embrittlement of alloys, due to several industrial applications, including those within the industrial value chain of hydrogen that is under development, which, according to European and international policies, are expected to contribute significantly to the replacement of fossil fuels by renewable energy sources. In the present study, the effect of hydrogen on the crack-tip fields of hydride- and non-hydride-forming alloys is examined. The crack-tip stress and hydrogen concentration distributions are derived under hydrogen chemical equilibrium, which is approached by considering the coupling of the operating physical mechanisms. In all cases, analytic relations are derived, thus facilitating integrity assessments, i.e., without the need to rely on complicated numerical methods, expected to lead to the development of respective tools in industrial applications. It is shown that, in the case of hydride precipitation, there are significant deviations from the K, HRR, and Prandtl fields, and, thus, the well-known approaches of Linear Elastic Fracture Mechanics (LEFM) and Elastic–Plastic Fracture Mechanics (EPFM) need to be accordingly modified/extended.

Application of equivalent distributed stress concept and modified cohesive zone model in elastic–plastic fracture mechanics analysis of surface cracks

Application of equivalent distributed stress concept and modified cohesive zone model in elastic–plastic fracture mechanics analysis of surface cracks

Development of Predictive Finite Element Models for Complete Contact Fretting Fatigue

Fretting fatigue is complex due to the interactions between contact mechanics and material fatigue properties. Predicting the total life in complete fretting fatigue is challenging due to different types of mechanical assemblies. This research develops a finite element model to predict this life, focusing on fatigue crack initiation and propagation in complete contact fretting fatigue. Crack initiation uses the Smith-Watson-Topper (SWT) criteria, considering wear and the material's elastic-plastic behavior. Crack propagation combines Linear Elastic Fracture Mechanics (LEFM), Elastic-Plastic Fracture Mechanics (EPFM), and Paris' law analysis. The SWT method with the addition of averaging shows good agreement with experimental data for crack initiation, possibly due to high singularities in complete contact. The combined LEFM and EPFM approach also aligns well for crack propagation. The estimated results had a 23% scatter compared to experimental data, demonstrating that combining damage and fracture mechanics provides a robust tool for predicting fretting fatigue life.

The Role of Welding in Fracture Mechanics Development

The role of welding in fracture mechanics development is considered from historical point of view. Starting point was analysis of Schenectady ship failure during the II World War, leading to development of linear elastic, as well as elastic-plastic fracture mechanics, soon afterwards. Two case studies are described to illustrate weldment fracture mechanics and structural integrity assessment.

SHORT-FATIGUE-CRACK GROWTH-RATE MODELING BASED ON THE J-INTEGRAL AS THE CONTROLLING PARAMETER

The local plasticity around the short fatigue crack tip fails to satisfy the basic assumption of linear-elastic fracture mechanics, which will lead to strong nonlinearity between da/dN and stress field strength indicator. Therefore, the elastic-plastic fracture mechanics parameter J-integral is employed to consider the non-uniform stress field. To this end, the in-situ observation system is set up to monitor and measure the short fatigue growth behavior in real time. The indicator ΔJ is analyzed based on recorded three-dimensional geometric parameters of the crack. The quantitative relationship is established to model the short fatigue crack’s growth rate.

Determination of the plastic J integral of ductile material using the XFEM with only Heaviside function and variable-node elements

Determination of the plastic J integral of ductile material using the XFEM with only Heaviside function and variable-node elements

Multiple cracking, crack coalescence and fatigue lifetime – Model and experiments on an austenitic steel and on a nickel base alloy

In many metals and alloys, low-cycle fatigue (LCF) and thermomechanical fatigue (TMF) generate a large number of surface microcracks. Using the replica technique, we document their growth and coalescence in the austenitic steel 1.4550 and the nickel base alloy Inconel 100. A model based on elastic–plastic fracture mechanics is developed, which considers the growth and coalescence of many coplanar semi-elliptical surface cracks. The results of the model are consistent with the experiments. An important conclusion is that the fatigue lifetime predicted by the multi-crack model is not substantially shorter than that predicted by a corresponding model assuming only a single semi-circular surface crack. This means that lifetime assessment can still be based on single-crack data, if one considers a factor 2 to include scatter and multiple-crack effects.

Enhancing the fracture resistance of additive manufactured polylactic acid via Morse-code-like architecturing

Enhancing the fracture resistance of additive manufactured polylactic acid via Morse-code-like architecturing

On the Origin of Extrinsic Size Effects on the Fracture Resistance of Thin ETP Copper Sheets

Size effects are well known to influence the mechanical behavior of materials and impact the structural integrity and reliability of devices such as thin films, coatings, foils, and sheet metals. There is little literature on extrinsic (specimen size) effects on fracture resistance of thin polycrystalline sheets while keeping the internal parameters constant. Herein, we determine the impact of specimen thickness on the fracture behavior of electrolytic tough pitch (ETP grade) Cu sheets, under two different grain sizes and initial dislocation densities. Elastic–plastic fracture mechanics (EPFM) combined with digital image correlation‐based full‐field strain mapping has been utilized to determine both the fracture resistance and plastic zone evolution as a function of specimen thickness. A smaller is weaker trend has been observed in both conditions. The specimen thickness effect is quantified in terms of a size exponent and is related to the truncation of the process zone ahead of growing crack, leading to reduced fracture resistance. The effect of intrinsic microstructural parameters such as grain size and dislocation density on the strain hardening ability, tensile elongation to fracture, and fracture toughness is also quantified and the plastic strain is found to correlate with fracture toughness.

Solutions of crack constraint parameter in 3D models − I: Through curve shape similarity

Solutions of crack constraint parameter in 3D models − I: Through curve shape similarity

Investigating the effects of steel strength and tensile overload level on fatigue crack growth performance

Investigating the effects of steel strength and tensile overload level on fatigue crack growth performance

Applicability investigation on failure assessment diagram of ASME code section XI - Appendix H for ferritic nuclear piping

Applicability investigation on failure assessment diagram of ASME code section XI - Appendix H for ferritic nuclear piping

A comparison of different experimental approaches in the determination of dynamic fracture toughness (J1d) behavior for RHA steel cost sustainable MMAW weldments

In the present investigation, the low hydrogen ferrite consumable weldment (weldment-1) and austenitic stainless steel consumable weldment (weldment-2) of rolled and homogenous armor steel (RHA) have been prepared with manual metal arc welding (MMAW). Further, the influence of weldments (weldment-1 and weldment-2) microstructure on the dynamic fracture toughness (J1d), strength, ductility and hardness has been evaluated and compared. The three different approaches have been utilized to estimate J1d for RHA weldments. Further, all three approaches’ outcomes have been compared with the elastic-plastic fracture mechanics (EPFM) approach through Jp-R curve. The results revealed that weldment-1 (yield strength 504.24 MPa and ultimate tensile strength 763.03 MPa) exhibited 26.93 and 25.07% more yield and tensile strength respectively than weldment-2 (yield strength 384.55 MPa and ultimate tensile strength 593.05 MPa). Further, the elongation of weldment-2 (elongation 42%) is 26.72% more than weldment-1 (elongation 32.10%). The joint efficiency and fusion zone hardness of weldment-1 are 5.85 and 57.56%, respectively more than weldment-2. The EPFM approach has good agreement with the correction factor approach (approach 2) and the compliance change rate approach (approach 3) with less than 7% difference in the estimation of dynamic fracture toughness of base metal and weldments (weldment-1 and weldment-2). Further, the percentage difference between maximum load point approach (approach 1) and the EPFM approach is more than 15% difference. The fractographic investigation confirms the ductile fracture in all under-investigated materials.

Microscopic fracture toughness of notched porous sintered Cu micro-cantilevers for power electronics packaging

To fulfill the high-temperature application requirement of high-power electronics packaging, Cu nanoparticle sintering technology, with benefits in low-temperature processing and high-melting point, has attracted considerable attention as a promising candidate for the die-attach interconnect. Comprehensive mechanical characterization of the sintered layer at a microscale is necessary to deepen the understanding of the fracture behavior and improve the reliable design of materials. In this study, microscale cantilevers with different notch depths were fabricated in a 20 MPa sintered interconnect layer. Continuous dynamical fracture testing of the microcantilevers was conducted in situ in a scanning electron microscope to detail the failure characteristic of the porous sintered structure. The microscopic fracture toughness of different notched specimens was obtained from the J-integral in the frame of elastic-plastic fracture mechanics. Specimens with deeper notches presented higher resistance to crack extension, while geometry factors of notch-to-width ratio between 0.20 and 0.37 exhibited a relatively stable microscopic fracture toughness ranging from 3.2 ± 0.3 to 3.6 ± 0.1 MPa m1/2.

Efficient technique for evaluation of three-dimensional elastic–plastic fracture mechanics parameters based on equivalent distributed stress concept

Efficient technique for evaluation of three-dimensional elastic–plastic fracture mechanics parameters based on equivalent distributed stress concept

Numerical fracture toughness evaluation of SS316L CT specimens using an Elastic Plastic Fracture Mechanics (EPFM) approach

Numerical fracture toughness evaluation of SS316L CT specimens using an Elastic Plastic Fracture Mechanics (EPFM) approach

Effect of Temperature and Ageing on Fracture Toughness of Alloy 617M

Effect of Temperature and Ageing on Fracture Toughness of Alloy 617M