Hybrid Experimental-numerical Approach Research Articles

An uncoupled ductile fracture criterion for a wide range of stress states in sheet metal forming failure prediction

In industrial production, sheet metal rupture will inevitably occur in the process of forming, especially in the shape of complex, relatively small thickness of the sheet. It is vital to accurately predict the failure of ductile metals under various working conditions. To deal with the problem, an uncoupled ductile fracture criterion (DFC) for a broad range of stress states is proposed based on the micro-mechanism of ductile fracture of metals, which redefines the relationship between the number of void nucleating and the equivalent plastic strain and takes into account the different deformation modes of the voids in the growth stage. Then, in order to verify the validity and advantages of the proposed DFC, the 3D fracture surface of AA 2024-T351 and AISI 1045 steel are constructed by the new criterion based on their fracture data under various stress states, and compared with the commonly used DF2016 criterion and Hu criterion. The prediction results show that the new criterion is better than them, both in terms of the maximum prediction error and the average prediction error. Furthermore, to further prove the effectiveness of the proposed model, five samples are designed for tension tests to calibrate the new DFC using a hybrid experimental–numerical approach, and the calibrated criterion is applied to cupping simulations of AA 6061 and compared with cupping experimental results. The results indicate that the Erichsen cupping number (IE) of the cupping simulation and experiment are 6.88 mm and 7.05 mm, respectively, and the error between them is only 2.411 %, and the location of the fracture is also basically the same. Therefore, all comparison results show that the proposed DFC can forecast the fracture problem in sheet forming more accurately under various stress states.

Anisotropic elastoplasticity and fracture of SCFR-PEEK composites in complex biaxial loading: Experiments and modelling

This research aims to gain insight into the anisotropic deformation and fracture behaviours of short carbon fibre reinforced polyether-ether ketone composites (SCFR-PEEK) under complex loading using experimental and modelling approaches. Novel biaxial tensile experiments using optimised cruciform specimens are designed and performed to study the anisotropic elastoplasticity and fracture behaviours of SCFR-PEEK in various stress states. An advanced anisotropic constitutive model was developed, experimentally calibrated, numerically implemented, and successfully verified by mechanical responses of biaxial tension with various stress ratios. Furthermore, using a hybrid experimental-numerical approach, the biaxial failure stress at crack initiation sites captured by a high-speed camera in biaxial tension was obtained. Employing experimental failure stresses at various uniaxial and biaxial stress states, a maximum stress based failure criterion was developed, which is coupled with the anisotropic elastoplastic model, thus enabling the description the anisotropic elastoplastic and failure behaviours under complex loading. The prediction of the failure of SCFR-PEEK in complex biaxial stress states using the coupled model is in good agreement with biaxial tensile experimental results using circular-notched specimens. Therefore, the developed model is verified to be capable of describing both elastoplastic deformation and fracture failure behaviours of SCFR-PEEK composites in complex loading.

A Study of the Dynamic Mechanical Properties of Q460D Steel

The dynamic mechanical properties of Q460D steel were studied to facilitate an assessment of the impact resistance of building structures. In the present work, material performance tests of Q460D steel at different temperatures, strain rates, and stress states were conducted. Using a hybrid experimental–numerical approach, a modified Johnson–Cook (JC) constitutive relation, a modified Johnson–Cook (JC) fracture criterion, and a lode-dependent fracture criterion were calibrated. To validate the calibration, Taylor impact tests of Q460D steel rods onto rigid target plates were carried out in a one-stage light-gas gun system. Mushrooming, tensile splitting, and petalling failure modes were obtained as the impact velocity was increased from 191.6 to 422.1 m/s. A three-dimensional finite element model was built for the Taylor impact tests, and FE simulations were run using the material models calibrated. It was found that the FE simulations using the lode-dependent fracture criterion were reasonable in terms of the failure modes of the Taylor rods. In contrast, the fracture behavior of the Taylor rods was significantly underestimated using the lode-independent JC fracture criterion. Finally, the effect of anisotropy, strain rate sensitivity and yield plateau on the Taylor impact FE predictions were explored and discussed.

Thermal softening behavior up to fracture initiation during high-rate deformation

This work proposes an innovative method to analyze the softening behavior due to adiabatic heat up to the fracture onset during high-rate deformation of AISI4340 steel at room temperature. To derive the rate- and temperature-dependent constitutive equation considering the post-necking behavior, uniaxial (UT) and notched tension (NT) specimens were tested at three strain rates of 10-3/s, 100/s and 103/s. The full fields of strain and temperature were measured until fracture initiation with high-speed digital and thermal imaging cameras, respectively. In particular, this research focused on observing the abrupt localized temperature increase in the post-necking phase, which was achieved through the use of a newly configured split Hopkinson tension bar (SHTB) system. It enabled an experimental investigation of the effect of adiabatic heat on localized behavior up to fracture at high strain rates (103/s). As the strain rate increased, the strain-localization occurred more quickly, and a higher temperature was experimentally observed at the location where fracture initiated. The experimentally measured thermal field was newly utilized for inverse optimization, to determine the thermal softening effect of the constitutive model considering adiabatic heat up to the onset of fracture including post-necking. Finally, a hybrid experimental-numerical approach was used to investigate the physical quantities of local strain, strain rate, temperature inside the specimen where fracture actually began.

Fracture mechanism and failure strain of TA31 titanium alloy for deep-sea pressure hulls based on continuum damage mechanics

Titanium alloys has high fatigue resistance, high corrosion resistance, high temperature resistance, and other excellent properties, and have been widely used in deep-sea equipment and aviation industries. In this paper, the fracture mechanism and failure strain of TA31 titanium alloy, which has been widely used in deep-sea equipment, were studied experimentally and numerically in different stress states. Considering the pressure sensitivity, the Modified Johnson-Cook (MJC) model and the Bonora damage model were used to study the fracture behavior. In order to obtain the parameters of models, four types of specimens under different stress triaxiality were conducted, and a hybrid experimental-numerical approach was employed in this paper. Then, the coupled constitutive elastic–plastic-damage model was developed and implemented in ABAQUS explicit finite element analysis (FEA) code. Finally, to validate the suggested model, FEA simulation was carried out and compared with the experimental results. The comparison revealed that the Bonora model with constant parameters was not enough to predict the failure strain. The damage parameters were sensitive to the stress triaxiality. In addition, the fracture morphology was observed by scanning electron microscope (SEM), which revealed the micro-mechanism of failure for TA31 titanium alloy. It is concluded that a higher stress triaxiality and shear mechanism lead to lower plastic deformation, and will inhibit the void growth on the damage evolution.

Role of build orientation on quasi-static and dynamic fracture responses of additively manufactured AlF357 and AlSi10Mg alloys

In this work, a popular additive manufacturing (AM) aluminum alloy - AlSi10Mg and a new AM aluminum alloy - AlF357 are fabricated using Laser-Powder Bed Fusion ( L -PBF) approach to evaluate quasi-static and dynamic fracture behaviors. Four build orientations - horizontal, vertical, flat, and diagonal - are assessed. A Kolsky pressure bar apparatus along with ultrahigh speed photography is used to carry out the dynamic fracture experiments. In-plane surface displacements near cracks are measured using Digital Image Correlation (DIC) to evaluate the fracture parameters directly. A hybrid experimental-numerical approach that combines DIC measurements and finite element analysis is implemented to extract critical energy release rate and crack growth resistance behaviors. The effect of build orientation is found to be significant on the quasi-static fracture behavior with the horizontal and flat orientations having the best and worst fracture responses, respectively. Under dynamic loading conditions, however, the effects of build orientation are marginal. Both AlF357 and AlSi10Mg show strain-rate sensitivity and change in fracture mechanism under dynamic loading conditions with ~175% and ~200% increase in critical energy release rate. AlF357 consistently outperforms AlSi10Mg in both quasi-static (~30%) and dynamic (~10%) loading conditions.

Modeling anisotropic ductile fracture of AA7075-T6 sheet for sheet metal forming considering anisotropic stress state

Anisotropic ductile fracture is one of the critical issues in the precision plastic forming of lightweight sheet metals. In this work, a new anisotropic ductile fracture model is developed by introducing the anisotropic stress triaxiality into the weight equation of the shear-controlled ductile fracture criterion. In an attempt to consider the effect of material anisotropy on stress state, the proposed fracture model is constructed in the anisotropic stress state form. The proposed anisotropic fracture model is used to characterize the anisotropic ductile fracture behavior of the AA7075-T6 sheet with a thickness of 2.0 mm under various stress states at room temperature. A series of uniaxial tensile tests are conducted using the in-plane shear specimen, the specimen with a central hole, and the plane strain grooved specimen to experimentally investigate the ductile fracture of AA7075-T6 along rolling, diagonal, and transverse directions. The proposed fracture model is calibrated by fracture strains determined from the hybrid experimental–numerical approach. With the calibrated fracture model, the anisotropic ductile fracture behaviors of AA7075-T6 over a wide range of stress states are predicted and compared with experimental measurements. The results show that the proposed fracture model successfully captures the anisotropic ductile fracture behavior of AA7075-T6 under various stress states at room temperature. Furthermore, to further illustrate the fracture predictive capability of the proposed fracture model, the predicted anisotropic fracture forming limit diagram is compared with the experimental forming limit strains obtained from the literature. Reasonable agreement is shown between literature data points and predicted fracture forming limit diagram. Accordingly, the proposed model has a great advantage in quantitative characterizing the anisotropic ductile fracture of high-strength aluminum alloy sheets under various loading conditions.

Prediction of forming limit curve for AA6061-T6 at room and elevated temperatures

Forming Limit Curve (FLC) has been widely adopted as a practical criterion for evaluating the formability of sheet metals. Predicting a reliable FLC by a virtual methodology could lead to robust process optimization before expensive tool manufacturing. In order to increase the predictive capabilities of the virtual forming tools, an accurate modeling of the forming limit curve should be considered at room and elevated temperatures. In this work, the isothermal forming limit curves of 6000 series aluminum alloy sheet metal are predicted by performing numerical simulations of Nakajima test. A stress triaxiality and Lode angle based ductile fracture criterion is used to determine the forming limit curve. Also, the ductile fracture criterion is extended to add the impact of temperature on ductile fracture prediction. The hybrid experimental-numerical approach is used to calibrate the ductile fracture criterion. The forming limit curve of AA6061-T6 sheet metal, with a thickness of 1 mm, is predicted using the calibrated ductile fracture criterion at room and elevated temperatures. Numerical simulations are performed in 3D with the finite element code Abaqus. The limit strains are determined for specimens undergoing deformation under different strain paths. Influence of temperature on the predicted forming limit curve is discussed.

Experimental and numerical investigation of ductile fracture for AA6061-T6 sheets at room and elevated temperatures

Warm forming is largely employed to enhance the poor formability of aluminum alloys at room temperature. The knowledge of the effect of stress state and temperature on the forming limits is an important aspect for the control of warm forming operations. Therefore, the objective of this work is to investigate the influence of temperature on the ductile fracture of AA6061-T6 aluminum alloy sheet metal under different stress states, ranging from shear to biaxial tension. For this purpose, experiments and numerical simulations of uniaxial tensile tests on dog-bone shaped specimen, notched specimens with different radius, specimens with a central hole and shear specimens are conducted at room and elevated temperatures. The hybrid experimental–numerical approach is used to identify the fracture strain and the corresponding stress state parameters (i.e. stress triaxiality and Lode parameter) to derive the fracture loci at room temperature, 150∘C and 200∘C. To accurately model the material behavior, the positive strain rate sensitivity in the flow stress response at elevated temperature is considered and attention is paid to constrain the finite element model by using the real experimental boundary conditions. The strain rate dependence of fracture strain is not considered in this work. A strong dependency of the ductile fracture on the temperature and stress state is evidenced. Also, an extension of Lou’s ductile fracture criterion which includes the impact of temperature on ductile fracture prediction is proposed. The prediction accuracy of the original and extended criteria is evaluated. It is found that Lou’s ductile fracture criterion is well suited to predict accurately ductile fracture at elevated temperatures under isothermal conditions whereas the extended form is very useful to predict ductile fracture initiation under non-isothermal conditions.

Prediction of Behaviour of Thin-Walled DED-Processed Structure: Experimental-Numerical Approach.

Additive manufacturing (AM) becomes a more and more standard process in different fields of industry. There is still only limited knowledge of the relationship between measured material data and the overall behaviour of directed energy deposition (DED)-processed complex structures. The understanding of the structural performance, including flow curves and local damage properties of additively manufactured parts by DED, becomes increasingly important. DED can be used for creating functional surfaces, component repairing using multiple powder feeders, and creating a heterogeneous structure with defined chemical composition. For thin parts that are used with the as-deposited surface, this evaluation is even highly crucial. The main goal of the study was to predict the behaviour of thin-walled structures manufactured by the DED process under static loading by finite element analysis (FEA). Moreover, in this study, the mechanical performance of partly machined and fully machined miniaturized samples produced from the structure was compared. The structure studied in this research resembles a honeycomb shape made of austenitic stainless steel AISI 316L, which is characterized by high strength and ductility. The uncoupled damage models based on a hybrid experimental-numerical approach were used. The microstructure and hardness were examined to comprehend the structural behaviour.

Counterexample-trained neural network model of rate and temperature dependent hardening with dynamic strain aging

Constitutive models dealing with the thermal and visco-plasticity of metals have seen wide applications in the automotive industry. A basic plasticity and fracture characterization of a 1.5 mm thick DP780 dual phase steel sheet based on uniaxial tensile (UT) experiments with seven distinct material orientations is complemented by low (∼0.001/s), intermediate (∼1/s) and high (∼150/s) strain rate experiments on notched tensile (NT) and shear (SH) specimens at temperatures ranging from 20 °C to 500 °C. At low strain rates, we observe a non-monotonic effect of the temperature on the force-displacement curves, with the highest curve obtained at 300 °C. Contrasting low speed tests, a monotonic effect of temperature is observed for intermediate and high strain rate experiments, with the highest curves obtained at 20 °C for both cases. Strain rate jump tests are performed proving the positive strain rate sensitivity of the steel. A machine-learning based plasticity model is developed to capture the observed complex strain rate- and temperature effect. The material is modeled as elasto-plastic, with a Hill’48 yield surface and a non-associated flow rule. The flow resistance is decoupled into a reference strain hardening term and a neural network term, which is a function of the plastic strain, strain rate, temperature, and an additional dynamic strain aging variable. The plasticity model is implemented into a material user subroutine and identified using a counterexample-guided hybrid experimental-numerical approach. The extracted loading paths reveal a complex rate and temperature effect on the ductility of DP780. A neural network based fracture initiation model is therefore adopted to describe the fracture onset across various stress states, strain rates and temperatures considered.

Hybrid assessment of acoustic radiation damping combining in-situ mobility measurements and the boundary element method

A hybrid experimental-numerical approach is proposed for assessing acoustic radiation damping – a major energy dissipating mechanism in lightweight structures. The vibrational behavior is characterized by distributed mobility measurements using laser Doppler vibrometry allowing to realistically capture the mechanical behavior of the structure under test. The experimentally obtained matrix of mobilities are coupled to a boundary element model to evaluate the radiated sound power numerically. Thereby, acoustic measurements and associated low frequency limitations are avoided, which results in two salient features of the proposed hybrid approach: modeling of diffuse incident acoustic fields and consideration of acoustic short-circuiting induced by slits and gaps. These features contribute to an accurate and excitation-dependent estimation of acoustic radiation damping in the low frequency range. The proposed hybrid approach is applied to flat and C-shaped aluminum sandwich panels mounted onto a tub-shaped foundation. The results are compared to those obtained by a previously reported numerical method.

Dynamic fracture behavior of additively manufactured Scalmalloy®: Effects of build orientation, heat-treatment and loading-rate

Scalmalloy® specimens are fabricated using Laser Beam Powder Bed Fusion to investigate the role of build orientation, loading-rate, and heat-treatment on critical energy release rate and crack growth resistance behaviors. Four build orientations - horizontal, vertical, flat, and diagonal - are assessed under dynamic loading conditions. The experiments are carried out in a split-Hopkinson pressure bar apparatus on edge-notched three-point bend geometries. The specimens with the horizontal build are studied also under quasi-static loading conditions to gain some insight into strain-rate sensitivity. The horizontal and flat build specimens are heat-treated for dynamic tests to study the effect of heat-treatment on high strain-rate fracture performance. The in-plane surface displacements near the crack are directly measured using Digital Image Correlation and ultrahigh-speed photography to evaluate the fracture parameters in each of these cases. A hybrid experimental-numerical approach that combines DIC measurements with finite elements is employed to evaluate the fracture behavior. The differences in the critical energy release rates and post-initiation fracture behaviors of Scalmalloy® under different conditions are quantified. The diagonal and horizontal builds outperform the vertical and flat builds in terms of dynamic crack initiation and growth characteristics. The quasi-static crack initiation and growth of the horizontal build specimens show significant strain-rate sensitivity relative to the dynamic counterparts. The heat-treatment of specimens result in marginal improvement of the dynamic fracture performance but does not affect the crack growth resistance behavior. Based on microstructural analyses, the melt-pool boundary orientation relative to crack front extension direction correlates well with the measured dynamic crack initiation and growth performance metrics.

Influence of temperature on the formability of an aluminum alloy

Warm forming is widely used as increasing the temperature is a solution to improve the formability of aluminum alloys. The stress (or strain) state is one of the most important factors affecting the formability of metals. In warm forming, the temperature and strain rate also play an important role on the deformation and fracture behavior. Figuring out the relationship between formability, temperature, strain rate and stress state is of great importance for providing more understanding of ductile fracture in warm forming conditions. Therefore, the objective of this work is to investigate the influence of temperature on the ductile fracture of a 6000 series aluminum alloy sheet metal under different stress states. Dogbone specimens, notched tensile specimens with different radius, tensile specimens with a central hole and shear specimens are used to cover a wide range of stress states. The hybrid experimental-numerical approach is used to identify the fracture strain and the corresponding stress state parameters (i.e. stress triaxiality and Lode parameter). To this end, fracture tests are carried out at 200°C using a tensile machine to determine the instant of fracture. Numerical simulations of the tensile tests are performed in 3D with the finite element code Abaqus to predict the strain field and calculate the evolution of the stress state. To accurately model the material behavior the positive strain rate sensitivity in the flow stress response at elevated temperature is considered. The results show a strong dependency of the ductile fracture on the temperature, strain rate and stress state.

Influence of experimental boundary conditions on the calibration of a ductile fracture criterion

Hybrid experimental–numerical approach is the commonly used technique to identify the material parameters of ductile fracture criteria. In this work, attention is paid to the precise definition of the Finite Element (FE) model of fracture tests by applying real boundary conditions coming from the local displacement field. The aim is to investigate the effect of the way to reproduce experimental boundary conditions on the accuracy of the hybrid experimental–numerical approach. A stress triaxiality and Lode angle based ductile fracture criterion is used to predict the onset of ductile fracture for AA6061-T6 aluminum alloy sheets. To calibrate this criterion, a series of fracture tests is carried out up to fracture. Notched tensile specimens with different radius, tensile specimens with a central hole and shear specimens are used to cover a wide range of stress states. Strain distribution over the surface is measured with digital image correlation technique. Two numerical models are defined for each geometry type, a first one constrained with real experimental boundary conditions and a second one with ideal boundary conditions, to predict stress and strain distributions. By comparing results of both approaches with experiments, it is shown that the model constrained by local experimental boundary conditions provides a better agreement with the experiments than the simplified model does, which underlines the sensitivity of the hybrid method to the adopted boundary conditions. Furthermore, several fracture test combinations are used to calibrate the ductile criterion and the effect of the calibration tests is discussed.

Ductile failure prediction of pipe-ring notched AISI 316L using uncoupled ductile failure criteria

The goal of this work is to predict ductile failure of pipe-ring notched AISI 316L specimens, where notches mimic the geometry of corrosion defects. Uncoupled damage models are used to that end. The Johnson-Cook and Lou-Huh criteria are calibrated.The uncoupled damage models are calibrated using experimental results from testing pipe-ring notched specimens. Calibration was achieved using a hybrid experimental-numerical approach. Six notch shapes are studied. Experimental matrices are designed to determine these shapes, and the pipe-ring notched specimen is inspired from the literature.Calibration of the uncoupled damage models require a ductile crack initiation indicator. The first indicator was based on the derivative curves of the force versus the connectors displacement curve. The second was based on the raw images of the gage section. The third was based on a percentage of the connectors displacement at fracture.Results show that ductile fracture depends on the Lode paramater. As a consequence, the Lou-Huh criterion is more effective at predicting ductile fracture than the Johnson-Cook criterion.

Investigations on the effect of roof types on wave impinging on a building: A hybrid experimental-numerical approach

Numerous efforts have been made to estimate the tsunami wave loads on structures, particularly box-shaped buildings (flat-roofed). As buildings have different types of roofs, insights into their respective wave flow mechanisms are important especially for the overtopping case. This study, therefore, focuses on the effect of roof types on tsunami-like waves impinging on a building. Through a series of wave flume experiments and numerical simulations, wave loads exerted on the front and back faces of a typical gabled-roof building were measured and compared with that of a box-shaped building. Results showed that the roof eaves caused the wave reflection and increased the upstream water depth, leading to an increment in maximum front face force up to 11% relative to the case of flat roof. Howbeit, less wave overtopping effect was demonstrated, thereby inducing a lower wave impact at the back of the building with a gabled roof. A ratio comprising the maximum flow depth and the story height of a building was then proposed, where the effect of gabled roof on the resulting maximum horizontal force was found to be insignificant to a ratio below 0.6. Finally, empirical equations to predict the maximum wave pressure on a building's front and back faces were formulated, which provide practical information for the design of a tsunami-resilient coastal building.

Calibration of the modified Mohr-Coulomb fracture model by use of localization analyses for three tempers of an AA6016 aluminium alloy

This paper presents a novel calibration procedure of the modified Mohr-Coulomb (MMC) fracture model by use of localization analyses and applies it for three tempers of an AA6016 aluminium alloy. The localization analyses employ the imperfection band approach, where metal plasticity is assigned outside the band and porous plasticity is assigned inside the band. Ductile failure is thus assumed to occur when the deformation localizes into a narrow band. The metal plasticity model is calibrated from notch tension tests using inverse finite element modelling. The porous plasticity model is calibrated by use of localization analyses where the deformation histories from finite element simulations of notch and plane-strain tension tests are prescribed as boundary conditions. Subsequently, localization analyses are used to establish the failure locus in stress space for proportional loading conditions and thus to determine the parameters of the MMC fracture model. Finite element simulations of notch tension and in-plane simple shear tests as well as two load cases of the modified Arcan test are used to validate the calibrated fracture model. The predictions by the simulations are in good agreement with the experiments, even though some deviations are seen for each temper. The results demonstrate that localization analyses are a cost-effective and reliable tool for predicting ductile failure, reducing the number of mechanical tests required to calibrate the MMC fracture model compared to the hybrid experimental-numerical approach usually applied.

Micro-structural Deformation Field Analysis of Aluminum Foam using Finite Element Method and Digital Image Correlation

Porous materials especially closed-cell metallic foams play important roles among novel materials because of their good characteristics e.g. high strength to weight ratio and crashworthiness. On the other hand, mechanical behavior determination and detailed characterization are essential in efficient manipulation and material tailoring. In the present research especial hybrid experimental-numerical approach is used for aluminum foam behavior determination as to the main goal, i.e. continuous deformation field measurement using digital image correlation (DIC) and finite element analysis (FEA) on porous specimen’s surface. To overcome the 3D modelling problem of closed-cell foams structure, we present the method based on CT-scan and digital optic microscope imaging combination. In the experimental part of the study, aluminum foams and proper specimens are manufactured, and then high-resolution digital imaging and illumination setup are employed. Finally, the deformation field is obtained using DIC. On the other hand, measurement verification and DIC parameters optimization processes are conducted using ABAQUS 2019 with comprehensive mesh independency study and response surface methodology (RSM) respectively as major research achievement. Finally, correlation equations based on high regression models are obtained. Using detailed geometrical micro-model and optimal DIC parameters yields to good numerical-experimental accordance. The novel approach of combined CT and digital microscope imaging instead of industrial micro-CT lowered imaging costs while yielded to accurate numerical results.

A novel method to determine the mixed mode (I/III) dynamic fracture initiation toughness of materials

A novel hybrid experimental-numerical approach is proposed to determine the mixed-mode (I/III) dynamic fracture initiation toughness of engineering materials. To demonstrate the methodology, cylindrical aluminum alloy specimens with V-notch spiral cracks on the surface at spiral inclined angles of $${\beta _{sp}=0}^{\circ }, {11.25}^{\circ }, {22.5}^{\circ }, {33.75}^{\circ }$$ and $${45}^{\circ }$$ are subjected to dynamic torsion load using a torsional Hopkinson bar apparatus. The torque applied at the onset of fracture is measured through strain gages attached to the incident and transmitter bars. Stereo digital image correlation (StereoDIC) is performed to measure the full field deformation and crack mouth opening displacement (CMOD) as a function of loading time. Results are used to estimate the crack initiation time. The dynamic stress intensity factors are extracted numerically based on the dynamic interaction integral method using ABAQUS. The mode-I $$ {(K}_{Id})$$, mode-III $$(K_{IIId})$$, and mixed-Mode ($$K_{(I/III)d})$$ dynamic initiation toughness data as a function of spiral angles are presented and discussed.