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Updated: 1 hour 21 min ago

job

Thu, 2024-01-04 20:13

In reply to International vacancies for post-doctoral researcher positions and other positions

Postdoc position Nazarbayev University

Dear iMechanicians,

Tue, 2024-01-02 12:32

In reply to Process parameter sensitivity of the energy absorbing properties of additively manufactured metallic cellular materials

Dear iMechanicians,

I hope this paper is of interest to the additive manufacturingarchitected materials, and dynamic impact (high strain rate) communities. 

Quasi-static and dynamic mechanical testing on stainless steel 316L cellular geometries is combined with material characterisation techniques to understand the interplay between additive manufacturing process parameters, geometry and mechanical performance (energy absorptionstrength). Four architected materials were studied, finding that the geometry had a greater influence on the investigated mechanical properties, relative to the Laser Powder Bed Fusion (LPBF) process parameter sets.

M. Simoes et al. Process parameter sensitivity of the energy absorbing properties of additively manufactured metallic cellular materials. Materials and Design, 224, 111398 (2022)

Application details and deadline

Sat, 2023-12-16 05:04

In reply to POST_DOC Position “A digital framework for the cutting of soft tissues: A first step towards virtual surgery” @ University of Genoa (Italy)

The Department of Civil, Chemical and Environmental Engineering of the University of Genoa is offering a post-doc position within the 2-years reasearch project PRIN 2022 PNRR “A digital framework for the cutting of soft tissues: A first step towards virtual surgery” focused on multiscale modeling of the complete cutting process in human brain tissues. The ideal candidate should have documented scientific experience in the study and development of physical-mathematical and computational models for describing the mechanics of soft tissues, and/or experiemce on peridynamic material modeling. The main objective of the work is to develop a constitutive correspondence framework to combine classical material models for brain tissues with the inherent capabilities of peridynamics to model (possibly evolving) discontinuities.

National coordinator (PI) of the PRIN project: Vito Diana

Research Units: University of Genoa, Italy; University of Brescia, Italy; University of Padua, Italy

Net Salary: ~1750 Eur per month

Application Deadline: Jan 10, 2024

 For more details on the position and how to apply, email to vito.diana@unige.it

or visit https://concorsi.unige.it/home/procedure/4366

a recent paper on rubber friction and wear may interest you

Thu, 2023-12-14 04:02

In reply to Journal club for December 2023 : Recent trends in modeling of asperity-level wear

Spectral wear modelling of rubber friction on a hard substrate with large surface roughnessH. TanakaS. YanagiharaK. ShiomiT. Kuroda and Y. OkuPublished:13 December 2023https://doi.org/10.1098/rspa.2023.0587

Debugging on linux (ubuntu)

Tue, 2023-12-12 07:36

In reply to Debugging standard user subroutines of ABAQUS

Thank you for the information. FOr those interested, here you can find a way of debugging your subroutine on linux:

https://github.com/alpinito1/Abaqus-vumat-linux-debug

Best,

Hi Tobias

Fri, 2023-12-08 03:59

In reply to Future directions?

Hi Tobias

Good to have your comment here. I also agree that course-graining/upscaling and more controlled/in-situ expeirments are two directions that need much more attention. 

I agree with you, Mike, on

Fri, 2023-12-08 03:18

In reply to temperature dependence

I agree with you, Mike, on this: surface energy and hardness are temperature-dependent very weakly, so the main contribution of temperature will be in the fracture energy and shear strength of the junction. Of course, the degree of temperature dependence varies between materials.

Regarding the Rabinowicz model, he used surface energy and that's one of the main differences between his model and our critical junciton size model. One should also note that these two models are fundamentally different, as the Rabinowicz model estimates the biggest size of particle that can detach and our model estimates the minimum size of asperity junction that leads to fracture and the generation of material fragments. We definitely needs more small-scale experiments in this direction to capture the effect of different parameters.

 

 

 

I agree with you, Mike, on

Fri, 2023-12-08 03:18

In reply to temperature dependence

I agree with you, Mike, on this: surface energy and hardness are temperature-dependent very weakly, so the main contribution of temperature will be in the fracture energy and shear strength of the junction. Of course, the degree of temperature dependence varies between materials.

Regarding the Rabinowicz model, he used surface energy and that's one of the main differences between his model and our critical junciton size model. One should also note that these two models are fundamentally different, as the Rabinowicz model estimates the biggest size of particle that can detach and our model estimates the minimum size of asperity junction that leads to fracture and the generation of material fragments. We definitely needs more small-scale experiments in this direction to capture the effect of different parameters,

 

 

 

Frictional heat vs plastic deformation

Fri, 2023-12-08 02:56

In reply to Dear Mike,

Deat Mike

Thanks for the comment and insightful questions.  As JF mentioned, we came across Reye's model by you also from one of your iMechanica post and that was one of the point we discussed in PNAS paper our https://www.pnas.org/doi/abs/10.1073/pnas.1700904114. 

In my opinion, the connection between the prefactor in Reye's model and the wear coefficient in the Archard model is still unclear. Both range from 0-1, but physically speaking, I am not sure they represent the same. 

 

Regarding heat contribution, we should distinguish between the frictional head and the head generated due to plastic deformation. Both Archard and Reye assumed a full plastic condition for the asperity junction, meaning that they excluded the sliding and resultant frictional heat in their model. In other words, for metals in dry condition, the main fraction of energy is converted to plasticity and material deformation, which eventually causes material removal. That's why the wear coefficient can be close to 1 in such cases. In the presence of lubrication or material oxidation, the shear strength of the junction reduces, increasing the contribution of frictional heat and reducing the degree of wear (this can be seen in our junction model as well, where reducing shear strength increases the critical junction size for debris formation, meaning a lesser probability for debris formation from asperity contact). Following what you proposed, one can reduce the degree of wear if a larger portion of sliding energy goes to frictional heat than plastic deformation. We should note that the generated heat at the contact can also damage the material surface and increase the wear rate, so as you mentioned, if a system is designed to remove heat as fast as possible, we should be able to reduce wear. 

 

Regarding the contribution of heat in the Rabinowicz model and our critical junction size model, the portion of heat generated due to plastic deformation is already considered, but not the contribution from head generated due to frictional sliding. The latter should come into play when we want to scale up from single to multiple asperities, as it identifies the probability of asperity failure. This information is missing currently and we need much more work. Also we need more contribution from experimental side to conduct systematic "clean" experiments. 

Frictional heat vs. plastic deformation

Fri, 2023-12-08 02:55

In reply to Dear Mike,

Deat Mike

Thanks for the comment and insightful questions.  As JF mentioned, we came across Reye's model by you also from one of your iMechanica post and that was one of the point we discussed in PNAS paper our https://www.pnas.org/doi/abs/10.1073/pnas.1700904114. 

In my opinion, the connection between the prefactor in Reye's model and the wear coefficient in the Archard model is still unclear. Both range from 0-1, but physically speaking, I am not sure they represent the same. 

 

Regarding heat contribution, we should distinguish between the frictional head and the head generated due to plastic deformation. Both Archard and Reye assumed a full plastic condition for the asperity junction, meaning that they excluded the sliding and resultant frictional heat in their model. In other words, for metals in dry condition, the main fraction of energy is converted to plasticity and material deformation, which eventually causes material removal. That's why the wear coefficient can be close to 1 in such cases. In the presence of lubrication or material oxidation, the shear strength of the junction reduces, increasing the contribution of frictional heat and reducing the degree of wear (this can be seen in our junction model as well, where reducing shear strength increases the critical junction size for debris formation, meaning a lesser probability for debris formation from asperity contact). Following what you proposed, one can reduce the degree of wear if a larger portion of sliding energy goes to frictional heat than plastic deformation. We should note that the generated heat at the contact can also damage the material surface and increase the wear rate, so as you mentioned, if a system is designed to remove heat as fast as possible, we should be able to reduce wear. 

 

Regarding the contribution of heat in the Rabinowicz model and our critical junction size model, the portion of heat generated due to plastic deformation is already considered, but not the contribution from head generated due to frictional sliding. The latter should come into play when we want to scale up from single to multiple asperities, as it identifies the probability of asperity failure. This information is missing currently and we need much more work. Also we need more contribution from experimental side to conduct systematic "clean" experiments. 

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