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This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Sven Düzel, Robert Eberlein, Hans-Jörg Dennig; Fatigue life analysis of POM gears with transient material modeling. AIP Conf. Proc. 8 May 2024; 3158 (1): 110015. https://doi.org/10.1063/5.0204543 and may be found at https://doi.org/10.1063/5.0204543., The today’s standard calculation methods for investigating the load carrying capacity of polymer gears (such as VDI 2736) are based on the same assumptions as for steel gears. Due to strongly varying material properties of polymers regarding stiffness level, nonlinearity and rate dependency, the predicted lifetimes of polymer gears are inaccurate. In the current study a rate dependent nonlinear viscoplastic finite element (FE) modelling of polyoxymethylene (POM) allows quantifying the material influences not considered by standard assumptions for metal parts. By deploying such a nonlinear material model for POM, a POMsteel gear pairing is investigated and additionally validated on a gear test rig. Different rotational speeds but constant brake torque are investigated to analyse the influence of inertia under the dynamic conditions as well as the rate depended material properties to the fatigue lifetime. An accelerated approach for a repeated transient FE modelling of the gear meshing process makes it possible to investigate critical stress and strain states over consecutive cycles, specifically focusing on tooth root breaking. It turns out that a cyclic increase of (plastic) strains occurs in the polymer gear teeth roots. Through an extrapolation of the local maximum principal strain, the strain state of the failure causing cycles can be analysed and forms the basis for a fatigue life analysis of POM gears. In combination with a strain based failure criterion the admissible number of cycles of POM gears for various rotational speeds is predicted and validated against experimental results obtained from the gear test rig.

In this work a strategy for numerical simulation of punching during concurrent pressing of stainless steel sheet metal has been investigated accounting for the stress triaxiality and Lode angle parameter. Modelling of the damage evolution of a sheet metal is a useful tool within the field of engineering and materials science, and can provide useful information regarding material capabilities in a design process. An inverse modelling approach was used, where both a material model and a damage model were developed. The damage model was developed using the GISSMO damage model (Generalized Incremental Stress State dependent damage MOdel) which incorporates the dependence on the stress triaxiality and the Lode angle parameter. The fracture strain is defined in the stress triaxiality and Lode angle parameter space as a surface and experiments were conducted to cover the space of the stress states. The modified Mohr-Coulomb fracture criterion was used to predict fracture strain in every stress state. The simulation software LS-DYNA was used for numerical modelling and the software LS-OPT was used to identify damage parameters. The results show good agreement with experimental data but due to issues with stress state characterization of the experiments, further validation is necessary before the damage model can be used in practice. The results from this work show a strong potential for the inverse modelling approach to model the evolution of damage using GISSMO. It was concluded that, in order to accurately describe the material behavior during punching, experimental data from a wide variety of stress states is necessary and the results from this work highlight the need of complete and accurate experiments. These findings are important for future development of damage models., Material behavior can be investigated from initial deformation until complete fracture using a damage model. In this article, a strategy for numerical simulation of sheet metal cutting is investigated for use in heat exchanger applications.

An anisotropic damage model is employed in order to simulate the fracture pattern of Bohus granite under quasi-static (Q-S) spherical indentation loading. The chosen damage description is added to the previously employed Drucker–Prager (DP) plasticity model with variable dilation angle. The resulting constitutive model is implemented to simulate the behavior of Bohus granite under indentation up to the load capacity of the material. The initial fragmentation, corresponding to the first small load-drop in the force–penetration curve, is likely due to the high radial tensile stress state at or close to the contact boundary. Both predicted fracture pattern and force–penetration results from the numerical simulation are compared to experimental data and a good agreement is found. The variability in tensile strength of the material is included in the chosen damage model by taking advantage of Weibull statistics. In this work, it is suggested that indentation test results by themselves may be used to calibrate the statistical distribution of tensile strength at small size scales such as in indentation applications., QC 20220609

The modeling of damage processes in materials constitutes an ill-posed mathematical problem which manifests in mesh-dependent finite element results. The loss of ellipticity of the discrete system of equations is counteracted by regularization schemes of which the gradient enhancement of the strain energy density is often used. In this contribution, we present an extension of the efficient numerical treatment, which has been proposed by Junker et al. in 2019, to materials that are subjected to large deformations. Along with the model derivation, we present a technique for element erosion in the case of severely damaged materials. Efficiency and robustness of our approach is demonstrated by two numerical examples including snapback and springback phenomena. © 2021 The Authors. International Journal for Numerical Methods in Engineering published by John Wiley & Sons Ltd.

This thesis presents the development of novel computational tools to overcome the limitations associated with damage modelling in laminated composite materials such as (i) high computational cost of accurately modelling stiffness and damage and (ii) high pre-processing effort for pre-inserting delamination and matrix-crack planes. A well-known example is the limiting mesh size requirement in cohesive zone modelling (CZM). To overcome these limitations a novel higher order cohesive element, discretising the numerical cohesive zone with multiple integration points within the element is developed, thereby enabling the use of large meshes. These cohesive segments are initiated adaptively between compatible continuum elements alleviating the necessity to pre-insert cohesive elements in a mesh. This method is termed higher order Adaptive Mesh Segmentation (AMS) and enables on-the-fly delamination modelling with large meshes. Implementation is performed with explicit time integration scheme in the commercial finite element solver LS-Dyna; this implementation provides easy access of these developments by industry. This method is verified using, (i) quasi-static double cantilever beam and (ii) soft body beam bending impact examples; a 50% reduction in the global number of degrees of freedom is obtained against conventional modelling methods. AMS is extended to linear elements for modelling delamination and matrix cracks as geometric discontinuities using mixed-time integration for efficient analysis with small elements forming ahead of a crack-tip. As an alternative, higher order elements are combined with an improved continuum damage mechanics method for modelling in-plane damage without mesh orientation bias. This method is demonstrated with ply-level discretisation by modelling damage propagation in (i) a laminate with an open-hole (i) a laminate subjected to a rigid body impact. The large mesh capability is further extended in the through thickness direction by modelling

A homogenisation scheme based on inclusion modelling is coupled with constitutive laws for damage and implemented in a finite element model for the simulation of concrete and reinforcement bar damage in reinforced concrete structures. The scheme is employed for simulating the behaviour of evenly distributed reinforcement and adapted for the simulation of zones with concentrated reinforcement in structural members. The model is validated against experimental tests from the literature carried out on reinforced concrete members subjected to bending and direct tension. The model captures the main characteristics of the behaviour of and damage in the constituent materials of reinforced concrete without resorting to individual meshing of the embedded bars and with very low computational cost., Peer Reviewed, Postprint (published version)

The main challenge for realizing competitive hybrid steel-FRP structures, such as bridges, carparks, is to make the steel and FRP components work together. In this study shear resistance, stiffness and ductility of three types of demountable bolted shear connectors are examined. Two blind-bolted M20 shear connectors and a novel, injected steel-reinforced resin (SRR) connection are selected to perform push-out experiments in web-core FRP decks. Failure modes of excessive bearing in FRP and bolt shear failure for blind-bolted and injected connectors, respectively, are identified. Nonlinear, highly detailed finite element (FE) models were also built and validated by results of the push-out tests to provide insights to the load-transfer mechanism. Analysis of internal forces and deformation through FE results reveals that blind bolted shear connectors provide high shear resistance and slip capacity thanks to the shear sleeves and catenary effects. The injected SRR connector shows distinct and centric load transfer owing to gapless design., Steel & Composite Structures

The main challenge for realizing competitive hybrid steel-FRP structures, such as bridges, carparks, is to make the steel and FRP components work together. In this study shear resistance, stiffness and ductility of three types of demountable bolted shear connectors are examined. Two blind-bolted M20 shear connectors and a novel, injected steel-reinforced resin (SRR) connection are selected to perform push-out experiments in web-core FRP decks. Failure modes of excessive bearing in FRP and bolt shear failure for blind-bolted and injected connectors, respectively, are identified. Nonlinear, highly detailed finite element (FE) models were also built and validated by results of the push-out tests to provide insights to the load-transfer mechanism. Analysis of internal forces and deformation through FE results reveals that blind bolted shear connectors provide high shear resistance and slip capacity thanks to the shear sleeves and catenary effects. The injected SRR connector shows distinct and centric load transfer owing to gapless design., Steel & Composite Structures

Predicting the life of a composite structure such as a wind turbine blade is not an easy task. This usually requires a multi-scale testing framework to specifically characterise the damage modes at different lengths scales and at the same time a multi-scale modelling framework that is mechanistic at its core. This is important as fatigue damage in com­posite laminates is multi-scale in nature. With this overarching goal in sight, this Ph.D. project studies the growth of tunnelling cracks under various biaxial loading conditions using a cruciform specimen and further builds a stochastic multi-scale damage model with mechanistic features which can have the potential to be applied to a structure. For the first time, crack density evolution plots from cruciform specimens are presented and also used to characterise a damage model. Further, it is of interest to investigate if a cruciform specimen can be the ideal coupon specimen in a multi-scale testing framework to recreate tunnelling cracks that may occur in structures under a realistic biaxial strain state. This Ph.D. project is part of a larger research group consisting of three joint Ph.D. projects (CASMaT Initiation Project), which are aimed at studying multi-scale fatigue damage as a result of tunnelling cracks at the sub-structural, meso- and the micro- length scales. The work in this project is primarily concerned with the meso-scale. Through extensive finite element analysis, the performance of various cruciform spec­imen designs are evaluated as a function of the anisotropy exhibited by multi-directional composite laminates. This is considered to be an important step towards standardising the cruciform specimen. It is seen that a single cruciform design for all material anisotropic configuration is not possible as the shape of the gauge zone, corners formed by the adjacent arms, the design of the arms, the layup configuration and the biaxial loading state largely affect the uniformity of the

This paper proposes an analytical model that uses historical damage dimension data to deduce physical impactor characteristics (size and energy) that has caused a certain resulting damage. Maintenance tasks occur in operations due to impact, however the source of the damage caused in the event remains in most cases unknown. Consequently, by inferring what has caused a certain type of damage from the distribution of the damage type and severity relative to impactor types, maintainers can be better prepared in terms of what to expect from a given impactor source. The developed model introduces a novel transition deformation region between the local deformation and the global plate deflection, allowing for fast and accurate predictions of the impact event. Using the known aluminium structural properties and damage dimensions, the damage data is converted into impactor data. The model is applied in a case study using 120 fuselage dent damages dimensions (length, width, and depth) from a Boeing 777 fleet. The results show that the model deduces impactor characteristics for 94% of the considered damages, ranging up to 240 J and 110 mm for impactor energy and radius respectively., Air Transport & Operations, Aerospace Structures & Computational Mechanics

It is commonly acknowledged that greenhouse gas (GHG) emissions from anthropogenic sources accelerate climate change impacts. Efforts are made by governments and companies to reduce GHG emissions via policies and actions. In order to determine which actions to prioritize among many options, benefits of emission reductions are often monetized, to compare with the costs of action or with benefits that can be obtained from other actions. Life cycle assessment (LCA) is a commonly used tool to assess the amount of GHGs emitted over the life cycle of a service, policy or product system. However, the damage modelling of GHGs in life cycle impact assessment (LCIA) and its monetary values have not been separately evaluated. This hinders the application of LCA in relevant decision contexts. This study evaluates the cause-effect chains and associated monetary values of GHG in three LCIA methods LIME2, EPS2015 and ReCiPe2016. Among these three, EPS2015 covers most damage categories, including the ones on human health, ecosystem and social assets. ReCiPe2016 does not include social assets damages and LIME2 does not consider ecosystem damages in climate change impact. Human health damages are well estimated in all three methods, contributing to 70–97% of the GHG monetary values. The lack of data is a clear obstacle across methods. Further research is needed to develop comprehensive and robust modelling approach for ecosystem damages, which are not well covered in current LCIA methods. Moreover, due to the scope of environmental LCA, there is a lack of consideration on socio-economic consequences, which may not be negligible for climate change. The resulting monetary value of GHG, expressed in per tonne CO2-eq are 16, 160 and 140 US$2017 respectively in LIME2, EPS2015 and ReCiPe 2016. These monetary values are reasonable for use in decision contexts where LCA is applied. Further research is, however, needed to reduce the current uncertainty of at least 1–2 orders of magnitude.

Computational homogenization has been used extensively over the past two decades for the analysis of masonry structures based on various averaging schemes (periodic homogenization, transformation field analysis,), focusing on regular periodic masonry. Irregular masonry has subsequently also been scrutinized using multiscale approaches. In such efforts, an efficient strategy is required for the generation and meshing of realistic representative volume elements (RVEs) geometries. In complement to existing generation approaches, the present contribution deals with a level set-based methodology to generate irregular masonry RVE geometries. Starting from inclusion-based RVEs, combinations of distance fields are used to produce typical geometries of irregular masonry RVEs. The resulting geometries are described by implicit functions. Such implicit geometry descriptions are next exploited in an automated procedure for producing high quality conformal 2D finite element meshes on implicit geometries. This automated RVE generation and discretization procedure is then illustrated by producing failure envelopes for irregular masonry, using an implicit gradient damage formulation. The interest of recently developed gradient models with decreasing interaction length parameters is also illustrated on a specific example., SCOPUS: ar.j, info:eu-repo/semantics/published

Nitrate concentration and runoff are site-specific and driven by climatic factors and crop management. As such, nitrate emissions may increase in the future due to climate change, affecting the marine eutrophication mechanism. In this context, and considering the case of spring barley production in Denmark, the paper has two objectives: (i) to estimate the present and future marine eutrophication impacts by combining a novel Life Cycle Impact Assessment (LCIA) modelling approach with a quantification of the effects of climate change on its parameterisation, and (ii) to discuss the implications of different normalisation references when comparing future Life Cycle Assessment (LCA) scenarios with current production systems. A parameterised characterisation model was developed to gauge the influence of future climatic-driven pressures on the marine eutrophication impact pathway. Spatial differentiation was added to the resulting ‘present’ and ‘future’ characterisation factors (CFs) and calculated for the Baltic and North Sea. The temporal variability of both midpoint normalised impact scores and damage scores reflect a 34% and 28% increase of the CFs in the North Sea and Baltic Sea, respectively. The temporal variability is mostly explained by CF variation and increasing future nitrogen flows. The marine eutrophication indicator scores at both midpoint and damage levels suggest that the differentiation of impacts to various receiving (and potentially perturbed) ecosystems is relevant. Damage scores are quantified with a factor 2.5 and 2.3 differentiation between the Baltic (higher) and North Seas (lower) for the present and future scenarios, respectively. The comparison of the normalisation methods, either based on total annual impacts (domestic inventory of background interventions), on ecological carrying capacity, or on the presently proposed method, point to the value of adding spatial differentiation to LCIA models. The inclusion of time variation and spatial diff

One of the shortcomings of nonlocal damage models with a constant length scale parameter is the wrong prediction of damage initiation and propagation in correspondence of a strongly inhomogeneous strain field. This unphysical behavior can be corrected by considering an evolving length scale which is made a function of the stress state. Giry, Dufour and Mazars (2011) have recently proposed an approach, based on an integral nonlocal damage model, which solves the problem of incorrect initiation and propagation of damage as discussed by Simone et al. (2004). In this contribution, a similar approach is presented in a differential damage model, the gradient-enhanced damage model. The underlying idea, which is used to modify the governing equations, is explained. A new formulation of the finite element equations is derived, with attention to C0-continuity requirements. Representative examples will illustrate the performance of the proposed approach. Shortcomings of the model are pointed out and graphically explained using slight variations of the before-mentioned examples., Building Engineering, Civil Engineering and Geosciences

One of the shortcomings of nonlocal damage models with a constant length scale parameter is the wrong prediction of damage initiation and propagation in correspondence of a strongly inhomogeneous strain field. This unphysical behavior can be corrected by considering an evolving length scale which is made a function of the stress state. Giry, Dufour and Mazars (2011) have recently proposed an approach, based on an integral nonlocal damage model, which solves the problem of incorrect initiation and propagation of damage as discussed by Simone et al. (2004). In this contribution, a similar approach is presented in a differential damage model, the gradient-enhanced damage model. The underlying idea, which is used to modify the governing equations, is explained. A new formulation of the finite element equations is derived, with attention to C0-continuity requirements. Representative examples will illustrate the performance of the proposed approach. Shortcomings of the model are pointed out and graphically explained using slight variations of the before-mentioned examples., Building Engineering, Civil Engineering and Geosciences