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• A microstructure-integrated acoustoplastic constitutive model for ultrasonic-assisted machining of Ti6Al4V alloy

  H. Bakhshan, E. Oñate, J. Carbonell

  CIRP Journal of Manufacturing Science and Technology (2025). Vol. 57, 14-31

  
  

  Abstract

  The ultrasonic-assisted machining (UAM) technology, compared to conventional machining (CM), has been proven to be an effective method for machining the difficult-to-cut Ti6Al4V alloy (TC4). In the UAM process, the evolution mechanism of microstructure and hardness directly influences the material behavior and consequently, mechanical response, which remains unrevealed from a computational perspective. To address this, in this study, we present a developed modeling technique that combines the Particle Finite Element Method (PFEM) with incremental homogeneous field distributions in a coupled manner to effectively predict the macro and micro response of the material in both CM and UAM processes. First, the evolution of microstructural parameters, including immobile dislocation density (IDD) and mobile dislocation density (MDD), dynamic recrystallization (DRx) grain size, and hardness, is incrementally developed and incorporated into the PFEM using internal state variables. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) model and Hall–Petch equation are employed for predicting grain size and hardness, respectively. Second, A microstructure-integrated acoustoplastic constitutive model is developed based on a modified Johnson–Cook (JC) model and average grain size (AGS) predictions dependent on ultrasonic vibration (UV) parameters. The proposed model is embedded into the PFEM to conduct a thermo-mechanical analysis capable of capturing the TC4 response, particularly in terms of serrated chip formation during CM and UAM processes. The model’s validity is checked through comparison with available experimental results in terms of chip shapes. Lastly, the predicted AGS and hardness in serrated chips and machined surface are compared with experimental data, showing good agreement. This suggests that the proposed acoustoplastic constitutive model, coupled with microstructure and UV parameters, can reliably analyze the CM and UAM processes of the TC4.

  Abstract
  The ultrasonic-assisted machining (UAM) technology, compared to conventional machining (CM), has been proven to be an effective method for machining the difficult-to-cut Ti6Al4V [...]

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• Fatigue delamination damage analysis in composite materials through a rule of mixtures approach

  A. Taherzadeh-Fard, S. Jiménez, A. Cornejo Velázquez, E. Oñate, L. Barbu

  Composite Structures (2025). Vol. 351, 118613

  
  

  Abstract

  The present study investigates delamination damage initiation and propagation within a homogenization theory of mixtures, using the concept of virtual layers and virtual interfaces. It eliminates spatial discretization of layers, introducing a resultant damage variable to capture structure’s bulk response under both monotonic and cyclic loads. Fatigue-induced deterioration is classified into sub-critical, critical, and over-critical stages based on interfacial stresses. Calibration is conducted employing the widely-available Wöhler curves for each loading mode independently. An advance-in-time strategy is included in the model to enhance the simulation speed. The reliability of the approach is assessed for crack initiation and propagation separately through standard test coupons, showing good correlation with experimental data in mode I, mode II, and mixed-mode loading conditions. Depending on the calibration procedure adopted, the model is applicable to a wide range of stress ratios. In addition, it could be integrated into any standard finite element framework using the desired number of elements through the thickness regardless of the physical amount of layers. This allows easy modification of stacking sequences or the number of layers within the constitutive law without mesh structure changes, facilitating simulation of large-scale composite laminates with minimal accuracy loss and reduced computational costs.

  Abstract
  The present study investigates delamination damage initiation and propagation within a homogenization theory of mixtures, using the concept of virtual layers and virtual interfaces. [...]

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• Multiscale data-driven modeling of the thermomechanical behavior of granular media with thermal expansion effects

  R. Rangel, A. Franci, E. Oñate, J. Gimenez

  Computers and Geotechnics (2024). Vol. 176, 106789

  
  

  Abstract

  A multiscale data-driven (MSDD) methodology is proposed for simulating the thermomechanical behavior of granular materials subjected to thermal expansion. The macroscale is handled using a continuous model based on the Finite Volume Method (FVM), while the microscale response is captured at Representative Volume Elements (RVEs) with the Discrete Element Method (DEM). To significantly reduce the computational cost of the analyses, the microscale DEM computations are not performed online, �.�., simultaneously with the macroscale FVM ones, as generally done in standard multiscale approaches. Instead, they are performed in advance to create a comprehensive database of RVE solutions under different initial conditions and thermal strains. This dataset is then used to train an Artificial Neural Network (ANN), which serves as a surrogate model for the macroscale solver. The MSDD approach is validated against pure DEM solutions of problems with distinct thermal conditions. Remarkably, we demonstrate that with only three input parameters, namely porosity, fabric, and thermal strain, the surrogate model can predict the microstructure evolution, as well as the updated conductivity and Cauchy stress tensors of the granular assembly. This allows for a generally accurate simulation of transient thermomechanical analyses at a drastically lower computational cost than the pure DEM approach.

  Abstract
  A multiscale data-driven (MSDD) methodology is proposed for simulating the thermomechanical behavior of granular materials subjected to thermal expansion. The macroscale is [...]

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• A critical review of how eXtended Reality (XR) has addressed key factors influencing Safety on Construction Projects (fSCPs)

  F. Rivera, J. Mora, E. Oñate

  Archives of Computational Methods in Engineering (2024). Vol. 31, pp.s 2015–2048

  
  

  Abstract

  The construction industry is known for its high accident rates. One hundred key factors affecting construction safety (fSCPs)—associated with general aspects of organisational management, materials and equipment, the construction site, and human aspects related to the worker and work team—have been identified. EXtended Reality (XR), which encompasses Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR) technologies, is being used in construction safety management. XR offers multiple advantages, given its characteristics of visualisation, immersion, and interaction with digital models and real objects. XR’s potential safety uses are widely recognised, and several studies have tested these technologies for different applications. However, most such efforts have been focused on identifying functionalities, applications, and technological aspects of XR in general, rather than studying whether those uses affect the factors relevant to security management. This study examined the literature on XR experiences that have addressed fSCPs and analysed how these developments have been related to the construction sector’s methodologies and technologies, such as building information modelling (BIM).

  Abstract
  The construction industry is known for its high accident rates. One hundred key factors affecting construction safety (fSCPs)—associated with general aspects of organisational [...]

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• A continuum–discrete multiscale methodology using machine learning for thermal analysis of granular media

  R. Rangel, J. Gimenez, E. Oñate, A. Franci

  Computers and Geotechnics (2024). Vol. 168, Art. Num. 106118

  
  

  Abstract

  This work presents a data-driven continuum–discrete multiscale methodology to simulate heat transfer through granular materials. The two scales are hierarchically coupled, where the effective thermal conductivity tensor required by the continuous method at the macroscale is obtained from offline microscale analyses. A set of granular media samples is created through the Discrete Element Method (DEM) to relate microstructure properties with thermal conductivity. The protocol for generating these Representative Volume Elements (RVEs) and homogenizing the microscale response is presented and validated by assessing the representativeness of the granular assemblies. The study found that two local properties, the porosity and the fabric of the material, are sufficient to accurately estimate a representative thermal conductivity tensor. The created dimensionless database of microscale results is used for training a surrogate model based on machine learning. In this way, effective thermal conductivity tensors that accurately reflect the local microstructure can be efficiently predicted from the surrogate model by taking the microstructural properties as inputs. The proposed multiscale methodology enables us to solve heat problems in granular media using a continuum approach with accuracy comparable to a pure discrete computational method but at significantly reduced computational cost.

  Abstract
  This work presents a data-driven continuum–discrete multiscale methodology to simulate heat transfer through granular materials. The two scales are hierarchically [...]

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• A modified Johnson–Cook model for the plastic behavior of metals in ultrasonic vibration-assisted upsetting processes

  H. Bakhshan, J. Carbonell, E. Oñate

  Journal of Manufacturing Processes (2024). Vol. 121, pp. 361-373

  
  

  Abstract

  In this work, we present a constitutive description of the plastic behavior of the metals and alloys under Ultrasonic Vibration (UV). When UV is imposed, it induces a softening effect on the plastic deformation of metals and alloys, referred to as the acoustoplastic phenomenon. The volumetric softening mechanism of the acoustoplasticity must consider stress superposition and acoustic softening. Taking the Johnson–Cook (JC) constitutive model as the reference for metal thermo-plasticity, the flow stress reduction due to UV is introduced by three types of softening terms: subtractive, multiplicative, and coupled. Those different configurations will be quantified via physical and phenomenological assumptions. For the study and validation of the proposed constitutive models, we focus on a well-known material, 6063 aluminum alloy. The ultrasonic vibration is modeled by an assisted upsetting process of an aluminum billet and compared with experiments. The impact of variations of the strain rate, ultrasonic amplitude, and frequency on the softening behavior of the models are analyzed and compared with available experimental results. We find out that the subtractive and coupled models agreed well with the experimental results showing the errors ranging from 2.4–4.8% and 4.4%–8%, respectively. However, the predictive ability of the multiplicative model exhibits large discrepancies at the low stage of strains following the acceptable predictions at high stains. By understanding the impact of the UV on the acoustoplastic deformation of the metals and alloys we can establish a reliable theoretical framework for prospective numerical studies of the UV-assisted manufacturing processes which is the goal of the current research presented here.

  Abstract
  In this work, we present a constitutive description of the plastic behavior of the metals and alloys under Ultrasonic Vibration (UV). When UV is imposed, it induces [...]

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• Hydromechanical embedded finite element for conductive and impermeable strong discontinuities in porous media

  D. Cavalcanti, C. Mejia, D. Roehl, I. de-Pouplana, E. Oñate

  Computers and Geotechnics (2024). Vol. 172, 106427

  
  

  Abstract

  The pore pressure inside oil and gas reservoirs compartmentalized by sealing faults increases during injection processes. The rise in the pore pressure can induce fault reactivation, leading to hydraulic issues such as fluid leakage from the reservoir to other layers and seismicity. Therefore, it is essential to accurately model the mechanisms involved in this problem, primarily related to the presence of a strong discontinuity, a fault, inside the domain. Several numerical approaches can be used to represent the presence of discontinuities. The embedded finite element method (EFEM) has recently gained attention because it does not require the mesh to conform with the discontinuities, thus circumventing the typical mesh generation challenges of modeling faulted domains. The current EFEM formulations cannot properly model a hydromechanical problem such as fault reactivation, due to simplifications in their derivation. Hence, this work proposes a new fully coupled hydromechanical EFEM formulation based on the Strong Discontinuity Approach that can represent discontinuities acting as preferential flow paths or barriers for the fluid flow. The formulation is applied to a fault reactivation problem, showing the main reactivation mechanisms. This paper also discusses the presence of spurious oscillations along the discontinuities and their relations with the mesh discretization.

  Abstract
  The pore pressure inside oil and gas reservoirs compartmentalized by sealing faults increases during injection processes. The rise in the pore pressure can [...]

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• The P-DNS method for turbulent fluid flows: An overview

  S. Idelsohn, J. Giménez, A. Larreteguy, N. Nigro, F. Sívori, E. Oñate

  Archives of Computational Methods in Engineering (2024). Vol. 31, pp. 973–1021

  
  

  Abstract

  An overview of the Pseudo-Direct Numerical Simulation (P-DNS) method is presented. This is a multi-scale method aiming at numerically solving the unknown fields at two different scales, namely coarse and fine. The P-DNS method is built around four key ideas. The first one is that of numerically solving both scales, which facilitates obtaining solutions to problems of both concurrent multi-scale and hierarchical multi-scale types. The second key idea is that of computing off-line the fine solution via Direct Numerical Simulation in simplified domains, termed representative volume elements (RVEs), while the third idea is that of storing the basic (physics-informed) results obtained from this solution in a problem-independent unique dimensionless database. This database may be subsequently used for solving different problems at the coarse level, i.e. by using coarse meshes in the corresponding problem domains, via a surrogate model. In this sense P-DNS resembles Reduced Order Methods, which require a previous off-line evaluation of the modes to be used in the solution, sharing with them the benefit of solving the reduced problem, more precisely the coarse scale, in P-DNS terms, in a very efficient way. The fourth and last key idea of P-DNS is based on the fact that most of the high-frequency modes of a turbulent flow are convected by the fluid velocity of the low-frequency modes. Taking this into account the P-DNS technique is implemented in such a way that the fine instabilities are convected by the velocity field of the coarse solution. Finally, although the P-DNS method has been used to solve different computational mechanics problems, such as convection-diffusion and convection-reaction/absorption problems, the scope of this overview will be limited to its application to turbulent incompressible fluid flows, including both single phase and particle-laden flows.

  Abstract
  An overview of the Pseudo-Direct Numerical Simulation (P-DNS) method is presented. This is a multi-scale method aiming at numerically solving the unknown fields at two different [...]

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• Microstructure evolution modeling of Ti6Al4V alloy during cutting using the Particle Finite Element Method and homogeneous field distributions

  H. Bakhshan, E. Oñate, J. Carbonell

  Journal of Manufacturing Processes (2024). Vol. 131, pp. 73-92

  
  

  Abstract

  This paper aims to explore the evolution of microstructural parameters induced during the cutting of Ti6Al4V alloy (TC4). The microstructure characteristics of the workpiece material is directly tied to its mechanical response during machining. During TC4 cutting, microstructure evolution is observed as a result of severe plastic deformations. The characterization of this phenomenon has significant interest from both academia and industry. In this work we present a developed modeling technique which combines the Particle Finite Element Method (PFEM) with incremental homogeneous field distributions. First, the PFEM is extended to perform a thermo-mechanical analysis capable of capturing the material responses of TC4 during orthogonal cutting. To generate serrated chips, an appropriate strain softening-based constitutive plasticity model i.e., TANH (Hyperbolic TANgent) is utilized. The PFEM’s validity is checked through comparison with available experimental results in terms of chip shapes and cutting forces. Second, the evolution of microstructural parameters such as dislocation density, vacancy concentration, dynamic recrystallization (DRx) grain size, and hardness is incrementally developed and incorporated into the PFEM using internal state variables as homogeneous field distributions. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) model and Hall–Petch equation are applied for predicting grain size and hardness, respectively. The parameters of the corresponding models are modified for TC4 to accurately capture their alterations. Lastly, the predicted results of the microstructure evolution in serrated chips and machined surfaces, including average grain size and hardness, are compared with experiments, demonstrating good agreement. This implies that the PFEM combined with microscale schemes can reliably simulate the machining process of the TC4.

  Abstract
  This paper aims to explore the evolution of microstructural parameters induced during the cutting of Ti6Al4V alloy (TC4). The microstructure characteristics of the workpiece [...]

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• Modeling of ultrasonic vibration-assisted micromachining using the particle finite element method

  H. Bakhshan, E. Oñate, J. Carbonell

  Computational Particle Mechanics (2024). Vol. 11, pp. 2267–2290

  
  

  Abstract

  When metals and alloys are exposed to ultrasonic vibrations (UV), a softening behavior occurs, caused by the phenomenon of acousto-plasticity. To obtain accurate results in a deformation analysis, this phenomenon must be included in the formulation of the constitutive material model. In this work, an acoustic-plastic model is proposed to capture the effects of ultrasonic vibrations during machining. The desired effect is to modify the chip morphology to reduce the magnitude of the cutting forces and thus reduce the energy consumption of the process. The study focuses on the modeling of ultrasonic vibration-assisted micromachining (VAMM). The particle finite element method is used and extended to perform a thermo-mechanical analysis capable of capturing the responses of conventional micromachining (CMM) and VAMM operations of 32 HRC stainless steel. The cutting speed and UV parameters, including amplitude and frequency, are integrated into the Johnson–Cook constitutive model to account for the effects of acoustic softening on the machining characteristics. The results show that the influence of UV on microcutting leads to thinner chips and lower cutting force. In the VAMM operations, an average reduction in cutting forces of 20% is achieved at five different cutting speeds. In addition, the contact length between the tool and chip decreases at different cutting speeds from 29% to a maximum of 44%. Furthermore, the thermal analysis results show that there is a negligible temperature change during the CMM and VAMM simulations, indicating that the study of the machining process can focus exclusively on its mechanical aspects when performed at the microscale. The predicted average chip thickness and effective shear angle of the workpiece material are in strong agreement with the experimental results, emphasizing the importance of considering acoustic softening in VAMM studies.

  Abstract
  When metals and alloys are exposed to ultrasonic vibrations (UV), a softening behavior occurs, caused by the phenomenon of acousto-plasticity. To obtain accurate results in [...]

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