Effect of isotropic and anisotropic damage and plasticity on ductile crack initiation

The formability limits of bulk metal forming in principal strain space and in the effective strain vs. stress-triaxiality space are characterized by an uncertainty region in which cracks may be triggered by tension (mode I of fracture mechanics) or by out-of-plane shear (mode III). The problem in obtaining experimental data in this region has been known for a long time and the main objective of this paper is to present a new upset formability test geometry that can effectively contribute to the characterization of the formability limits of bulk metal forming parts subjected to biaxial tension. Alongside with this objective, this paper also presents an analytical expression for converting the fracture forming limit line corresponding to crack opening by mode III in principal strain space into a hyperbolic fracture limit curve in the effective strain vs. stress-triaxiality space. The overall methodology employed by the authors combines experimentation along with analytical and numerical modelling, and the contents of the paper is a step towards diminishing the actual lack of knowledge regarding failure by fracture in bulk metal forming parts subject to stress-triaxiality values beyond uniaxial tension. Results show that a new uncoupled ductile fracture criterion built upon combination of the integrands of the Cockcroft-Latham and McClintock criteria can be successfully used to model the physics of the bulk metal forming limits for the entire range of stress-triaxiality values corresponding to cracking on free surfaces.

Section: Introductionmentioning

confidence: 99%

Revisiting the fracture forming limits of bulk forming under biaxial tension

Sampaio

Pragana

Bragança

et al. 2022

“…The future work should involve in developing a constitutive model or numerical model as seen for soil and concrete (Liu et al., 2018). The effect of freeze–thaw cycles on evaluating the compressive strength and crack potential need to be studied as seen for other composite soils (Cao et al., 2018; Keshavarz and Ghajar, 2019).…”

Section: Future Workmentioning

confidence: 99%

Influence of biochar from animal and plant origin on the compressive strength characteristics of degraded landfill surface soils

Bora

Bordoloi

Kumar

et al. 2020

Growing awareness of sustainability in the landfill cover system has increased the use of biochar amendment for degraded landfill surface soils. Hydraulic and vegetative benefits of biochar on cover soil have been studied in the past, while ignoring mechanical characteristics, which is important to understand progressive failure of landfill infrastructure. In this study, the mechanical characteristics of four soil–biochar composites were investigated by conducting 81 unconfined compressive strength test. The results based on four in-house produced biochar were used to study the effect of compaction state (density, moisture content) and biochar percentage (5% and 10%) on unconfined compressive strength of soil–biochar. The ductility of soil–biochar was investigated for all the four biochars. Results from this study indicate a contrasting observation of strength gain depending on the type of biochar. The unconfined compressive strength of soil–biochar is potentially influenced by the different surface functional groups of biochar (hydrophilicity/hydrophobicity) and soil-biochar interlocking. It was noted that the peanut shell biochar gave comparable unconfined compressive strength of soil–biochar with that of bare soil for different compaction state. However, a diminution in the unconfined compressive strength was observed for all the other three soil–biochar sourced from water hyacinth, saw dust, and poultry litter. The study indicates that the use of biochar in soils does not ensure an improvement in the strength of soil–biochar. Enhancement in ductility was found for all the four soil–biochar irrespective of compaction state. Improvement in ductility was maximum when the soil–biochar is compacted at the dry state of optimum. Plant-based biochar has higher potency to increase the ductility of soil as compared to the animal-based biochar. Our study identifies peanut shell biochar ideal for landfill cover amendment material, considering its mechanical characteristics and design criterion. Soil biochar composite from water hyacinth, saw dust, and poultry litter can be used for potential application in green-infrastructure.

“…In order to maintain long-term service in the section of the roadway, the roadway is generally dug along the roof of the coal seam to increase roof stability and integrity, during the layout of the coal mine roadway. That has achieved good application results in some roadways with low roof pressure and good roof integrity (Keshavarz and Ghajar, 2018; Ma et al., 2017; Ma and Wang, 2019; Xu et al., 2017; Zhang et al., 2014, 2019). However, this also exposed some problems, such as the roadways affected by the mining pressure, and the “island” roadways mined on both sides.…”

Section: Introductionmentioning

confidence: 99%

Research on strain softening constitutive model of coal-rock combined body with damage threshold

Wang

2021

The coal seam and the roof of the roadway bear loads together in the underground engineering of coal mine. Especially for the roadway driven along the roof, its deformation is completely different from that arranged in the complete rock stratum. Accurately knowing the mechanical mechanism of coal-rock combined body can help understand the deformation and failure modes of such roadways. This article started with tests of coal-rock combined samples with different height ratios, based on the test results, a strain softening damage constitutive model of coal-rock combined body and a method for solving the parameters of the model were proposed, and the influence of the model parameters was discussed. The test results show that the stress peak value and residual strength of the coal-rock combined samples are negatively correlated with the proportion of coal in the coal-rock combined samples, and have a positive correlation with the confining pressure. The damage constitutive model fitted the test curve well. The model can accurately describe the stress-strain curve of coal-rock combined samples, and can reflect the influence of different height ratios of coal and rock samples and confining pressures. The effects of model parameters were discussed based on the damage constitutive model, which are expected to be widely used in underground engineering.