Fracture - Science topic

Dear Mehrab,

Thank you for your thoughtful question regarding the computation of Normalized Total Fracture Energy (GF) in concrete specimens, particularly in the context of varying geometric dimensions.

You are correct that the total fracture energy (GF) is typically determined as the area under the load–displacement (or load–CMOD) curve divided by the fractured ligament area, which for a notched beam is usually expressed as:

GF=WfAlig=∫0δuP(δ) dδb⋅(d−a)G_F = \frac{W_f}{A_{\text{lig}}} = \frac{\int_0^{\delta_u} P(\delta) \, d\delta}{b \cdot (d - a)}GF​=Alig​Wf​​=b⋅(d−a)∫0δu​​P(δ)dδ​

Where:

To normalize GFG_FGF​, researchers often aim to account for geometric effects (e.g., size, shape, or volume dependence) in order to make energy values comparable across specimens of different dimensions. A common method is to normalize fracture energy by a characteristic length, a nominal strength, or by using dimensionless formulations.

One widely accepted approach (as recommended in RILEM TC 50-FMC and by Hillerborg) is to normalize GFG_FGF​ by the tensile strength ftf_tft​ and elastic modulus EEE to obtain a characteristic length lchl_{ch}lch​:

lch=E⋅GFft2l_{ch} = \frac{E \cdot G_F}{f_t^2}lch​=ft2​E⋅GF​​

However, if you're strictly referring to normalized GF with respect to geometry, an alternative is to use:

GF,norm=GF(d−a)G_{F,\text{norm}} = \frac{G_F}{(d - a)}GF,norm​=(d−a)GF​​

Or more generally:

GF,norm=Wfb⋅(d−a)2G_{F,\text{norm}} = \frac{W_f}{b \cdot (d - a)^2}GF,norm​=b⋅(d−a)2Wf​​

This accounts for ligament length scaling, often used when comparing fracture energies across specimens with varying ligament heights.

The choice of normalization method should align with the goal of your analysis—whether for size effect compensation, comparison across studies, or scaling analysis. Always document the rationale behind the selected normalization approach in your methodology.

Should you require a deeper discussion or example calculation templates in MATLAB or Excel, I’d be happy to assist further.

Warm regards, Dr. Gitonga Muriithi

It is a paper published in Injury in 2021.

Hi Ali,

I'm not sure I understand your questions. I have some comments below.

Regards,

Simon

A temperature where a sharp drop in energy is observed. Almost nil ductility.

Fracture Mechanics in Cement-Based Materials, focusing on fracture toughness, fracture energy, and crack propagation in quasi-brittle materials like concrete:

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References for Fracture Mechanics in Cement-Based Materials

1. Bazant, Z. P., & Planas, J. (1998).

Fracture and Size Effect in Concrete and Other Quasibrittle Materials.

CRC Press.

A seminal book that covers the theory and application of fracture mechanics in concrete and cementitious materials.

2. RILEM TC 50-FMC (1985).

Determination of the fracture energy of mortar and concrete by means of three-point bend tests on notched beams.

Materials and Structures, 18(106), 285–290.

Standard procedure to determine fracture energy, widely used in experimental research.

3. Mindess, S., Young, J. F., & Darwin, D. (2003).

Concrete.

Prentice Hall.

Comprehensive textbook that introduces fracture mechanics in concrete materials.

4. ASTM C1609 / C1609M – 19.

Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading).

This test method assesses post-cracking behavior and is often applied in fracture studies.

5. Wittmann, F. H. (1983).

Fracture Mechanics of Concrete: Applications of Fracture Mechanics to Concrete, Rock and Other Quasi-Brittle Materials.

Elsevier.

Discusses nonlinear fracture mechanics and cohesive crack models in concrete.

6. Shah, S. P., & Swartz, S. E. (1995).

Fracture Mechanics of Concrete: Applications of Fracture Mechanics to Concrete, Rock and Other Quasi-Brittle Materials.

John Wiley & Sons.

Focuses on experimental methods and numerical approaches to understanding crack propagation.

7. Bazant, Z. P. (2002).

Concrete fracture models: testing and practice.

Engineering Fracture Mechanics, 69(2), 165–205.

Discusses fracture models like cohesive zone and size effect law in the context of practical testing.

8. JCI-S-001-2003.

Method of test for fracture energy of concrete by use of notched beam.

Japan Concrete Institute.

A standardized method from Japan for determining fracture energy in notched concrete beams.

Links:

Certainly! Here are the references for Item 2: Fracture Mechanics in Cement-Based Materials, along with links to access the documents:

1. Bažant, Z. P., & Planas, J. (1998).

Fracture and Size Effect in Concrete and Other Quasibrittle Materials.

CRC Press.

Access the document

2. RILEM TC 50-FMC (1985).

Determination of the Fracture Energy of Mortar and Concrete by Means of Three-Point Bend Tests on Notched Beams.

Materials and Structures, 18(106), 285–290.

Access the document

3. Mindess, S., Young, J. F., & Darwin, D. (2003).

Concrete (2nd Edition).

Prentice Hall.

Access the document

4. ASTM C1609 / C1609M – 19.

Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading).

Access the document

5. Wittmann, F. H. (1983).

Fracture Mechanics of Concrete: Applications of Fracture Mechanics to Concrete, Rock and Other Quasi-Brittle Materials.

Elsevier.

Access the document

6. Shah, S. P., & Swartz, S. E. (1995).

Fracture Mechanics of Concrete: Applications of Fracture Mechanics to Concrete, Rock and Other Quasi-Brittle Materials.

John Wiley & Sons.

Access the document

7. Bažant, Z. P. (2002).

Concrete Fracture Models: Testing and Practice.

Engineering Fracture Mechanics, 69(2), 165–205.

Access the document

8. JCI-S-001-2003.

Method of Test for Fracture Energy of Concrete by Use of Notched Beam.

Japan Concrete Institute.

Access the document

Please note that access to some of these documents may require subscriptions or institutional access.

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Dear Eng Marcos Youssef Lahzy

Here are direct links to the articles I found on the fracture properties of cement-based composites and green binder mixtures:

Thanks

Hello. You are programming models from various materials. Did I understand you correctly?

Joints and fractures act as pathways for groundwater and hydrocarbons by increasing the permeability of rocks, allowing fluids to move more easily through the connected voids.

There's a risk of nonunion, malunion, prolonged pain with ambulation, poor return to activity without acute management of rest and limited activity. Follow up is useful for evaluation of fracture healing and if further management modifications are needed.

Ahmed Ibrahim Morshedy Thank you so much! Do you know if this syntax also works for the acute version of the SF12v2 (with a 7 days recall period)? I am not sure if the norm values are the same. I would appreciate your help very much!

To determine the maximum principal stress and normal and shear mode fracture energies for MO40 steel in an Abaqus XFEM analysis, you'll need to obtain these material properties through experimental testing (like fracture toughness and mixed-mode fracture tests) or literature review (material data sheets, research papers, or material databases). Once obtained, input these properties into Abaqus by defining a material with elastic properties, maximum principal stress criterion, and mixed-mode fracture energy as a function of mode mix ratio. Create a section, mesh the model with a fine mesh around the crack path, and define the XFEM analysis with crack initiation and damage evolution parameters. Remember to consider factors like uncertainty, temperature effects, and rate effects when interpreting results.

Yanjie Bai , Bhavanasi Subbaratnam thanks a lot for your answers it helps !

I tried to insert a contact debonding , i initially have a bonded contact between the carbon fiber and epoxy , i've defined a material (fracture energies bases debonding ) since i can't define it with a traction separation law ( it is reserved for the delamination interface ) , however it debond at first , then i have a sliding between the epoxy and carbon ...actually my question is : should i try again to modify the mesh, material properties to have better results or should i give up on contact debonding and try to insert interface delamination ?

We provide G values for Double-Cantilever Beam (DCB) specimens that depend linearly on the crack length c: see " DOUBLE-CANTILEVER BEAM SPECIMEN BENT BY PAIRS OF OPPOSITE TERMINAL TRANSVERSE LOADS" (2024) in our contributions in Research Gate.

The PEEQ values for monotonic and cyclic loading will undoubtedly differ. In cyclic loading, plastic strain accumulation is generally higher, as it depends largely on the number of cycles endured and the specific loading protocol. In contrast, for monotonic loading, PEEQ may be relatively lower, since the specimen isn't subjected to reversed loading. This could explain why your numerical model shows premature failure compared to the experimental data. For more insights into PEEQ (at fracture) variation under different stress states in mild steel subjected to monotonic loading, you may refer to our article: https://doi.org/10.1016/j.engfracmech.2023.109638.

Jp Wu Nice suggestion. Thank you for your reply.

I'm not sure how you would use a circular specimen geometry to measure fracture toughness using a J-integral method. You will likely need to provide more details of your testing methodology in order for others to weigh in.

In our lab we use commercial products based on orthophosphoric acid. However, it should be remembered that after this a protective oxide film is created on the surface. If you need to examine the surface structure, this can be a problem.Recently I tried using a cheaper option - citric acid. It takes more time. However, there is an effect.

Timothy Imanobe Oliomogbe

Hydrologic modeling is a critical tool in water resource management and environmental protection, as it helps predict and manage the water cycle and its components, such as river flows, groundwater levels, and rainfall intensity. However, in this process we often encounter data gaps and challenges in understanding complex hydrological processes. Here's how these aspects relate to each other and how they can be managed:

What is hydrological modeling? General description: Hydrological modeling involves the use of mathematical and statistical models to simulate and predict hydrological processes, such as river flow, precipitation, evaporation and infiltration. These models can be simple or very complex, depending on the purpose and scope of the study.

Types of models: Models can be physical (based on the principles of physics and hydraulics), statistical (using historical data) or a combination of both (hybrid models).

Purpose and applications: Water resources management: Models help in managing water reserves, designing hydropower plants, planning and designing infrastructure. Flood Risk Assessment: Models can predict flood risks and help develop protection and preparedness measures. Sustainable Development: Hydrological models support sustainable land and water management practices.

Sources of data gaps: Lack of data: In some regions, especially in developing countries or remote areas, data on precipitation, flow and other hydrological parameters may be limited or completely unavailable. Inadequate resolution: Data may be collected at a level that is too coarse or unsuitable for accurate modeling.

Suboptimal observation periods: Long-term changes in climate conditions and water resources may require data from longer periods of time, and in some cases, data may only be available for shorter time intervals.

Methods to improve understanding: Model calibration and validation: Periodic adjustment and testing of models based on real data can help improve accuracy and reliability. Use of advanced techniques: Methodological techniques such as multi-resolution modeling, use of high-fidelity models, and complex simulations can improve process understanding.

Hydrological modeling is essential for understanding and managing water resources, but it often faces challenges such as data gaps and the complexity of hydrological processes. Managing data gaps and using advanced modeling and analysis techniques can help improve the accuracy and reliability of hydrological models. The integration of these aspects allows for better management of water resources and a more efficient response to challenges such as floods and droughts.

I have solved many such problems using FRAC3D-VS, which is available free and has many related publications. This is just one example of many. Note: RG will no longer animate GIFs but your web browser can.

1) Your answer is on a purely assumption level.

2) Assuming no pre-existing crack, le material would deform plastically only.

3) In presence of a pre-existing crack, expansion of the latter would be observed on the elastic applied stress range first until the blunting of the crack (crack arrest), clearly in a two-dimensional crack scheme.

Cross-slip, twinning, and fracture systems under applied loadings receive the same mathematical theory using continuous distributions of elliptical dislocations in the framework of linear elasticity. Essentially the theory provides a quantity G that is a ratio, defined as the decrease ΔE of the total energy of the system divided by the corresponding change ΔS of the surface of the dislocation distribution, after incremental infinitesimal time dt: G= -ΔE/ΔS. In fracture G is the energy release rate or crack-extension force per unit length of the crack-front. Stationary configurations under which d<G> = 0 are those observed experimentally. <G> is the value of G averaged over all the spatial positions on the defect front. Please refer to the following works for details: Conoidal crack with elliptic bases, within cubic crystals, under arbitrarily applied loadings-I. Dislocation, crack-tip stress, and crack extension force; -II, III, and IV: Application to systems of twinning in copper (II), fracture in CoSi2 (III), and cross-slip in copper (IV). Theory and experiments completely agree.

Jos Wielders Thanks for your answer. While classical markers such as CTX and P1NP have their utility, they have often failed to predict fractures, especially in older populations. This is why i am asking for the most promising

The following link is also very useful: https://www.sciencedirect.com/topics/materials-science/cleavage-fracture

The human cortical bone typically experiences maximum strain levels ranging from 0.7% to 2%. Beyond this range, the bone may reach its failure point, resulting in fracture. It's important to note that various factors such as bone density, mineral content, and structural integrity can influence the specific strain levels at which cortical bone may fracture. Additionally, the rate of loading and the direction of force applied also play significant roles in determining the strain threshold for bone fracture.

Hey there Bouabid Misski!

When it comes to applying mechanical stress to ceramics without risking fracture, precision is key. Here are some optimal techniques to achieve uniform stress distribution:

1. **Hydrostatic Pressure**: This method involves subjecting the ceramic material to pressure from a fluid, which applies force uniformly in all directions. It's particularly effective for delicate ceramics.

2. **Hot Isostatic Pressing (HIP)**: HIP involves applying high pressure and temperature simultaneously to the material. This helps in compacting the ceramic, reducing defects, and ensuring uniform stress distribution.

3. **Cold Isostatic Pressing (CIP)**: Similar to HIP, but performed at room temperature, CIP involves subjecting the ceramic to pressure from all directions using a fluid medium. It's useful for shaping and densifying the material.

4. **Electrostrictive Actuators**: These devices apply mechanical stress through the application of an electric field. They can offer precise control over stress distribution, making them suitable for certain applications.

5. **Finite Element Analysis (FEA)**: Before applying stress physically, utilizing FEA can help in simulating stress distribution and optimizing the design to minimize areas of high stress concentration.

Remember, the choice of method depends on factors like the material properties, desired outcome, and manufacturing constraints. Experimentation and testing are essential to determine the most effective approach for your specific application.

Feel free to ask if you Bouabid Misski need more details or assistance with anything else!

My scientific work does not belong to that field.

This difference can be attribute to different in testing conditions ( strain rate, anisotropy, tool parameters in FLC, friction)

Phenomena such as the Al Naslaa Rock, Active cracks in Yosemite National Park find explanation from gravitational forces.

Скажется, только не в виде пластичного хвостика, а в виде ступеньки, всё-таки это не пластическая деформация, а разрушение. Так это выглядит для непрерывных волокон. У дисперсных композитов, возможно, будет более гладкий спуск.

Again @Vladimir Dusevich is stalking me and copying an using chatgpt to rephrase my answer. Stop bullying me.

Corentin Levard, I'm sorry to bother you again. After checking the official Abaqus documentation, I think you may be wrong, as the Abaqus documentation indicates that the failure strain calculated by the Johnson-Cook damage model should correspond to the equivalent plastic strain at the onset of the damage, Instead of the equivalent plastic strain corresponding to the final fracture point.

Martin Brandtner-Hafner, tensile tests are not specifically designed for fracture pattern analysis. This is because tensile tests are designed to measure the overall behavior of a material, while fracture pattern analysis is concerned with the behavior of a material at a local level.

Dear Nidhi Chaubey

The square notch you mentioned might be providing a stress concentration that leads to accelerated crack propagation. If the square notch geometry creates a more severe stress concentration compared to other notch shapes, the crack might propagate more rapidly.

Amir Janghorban Thanks for your response. The problem was the number of layers that Abaqus couldn't solve with my system, so I have just equated the number of layers with a simple equation.

It is possible to estimate pore pressure, fracture gradient, and mud weight window using only Microsoft Excel. Here's a general approach:

1. Collect the necessary data: You will need well log data (such as resistivity, sonic, and density logs) and drilling data (such as formation depths, mud weight, and drilling fluid properties) for the well you are analyzing.

2. Create a new Excel spreadsheet and enter the data into the appropriate cells. Organize the data into columns and label each column with a descriptive heading.

3. Calculate the pore pressure using one of several methods, such as the Eaton method or the Bowers method. These methods use different equations to estimate pore pressure based on well log data. You can find these equations online or in textbooks on well logging and formation evaluation. Here's an example of how to use the Eaton method:

- Calculate the normal compaction trend line for the formation using the density log and the depth values.

- Calculate the overburden pressure using the normal compaction trend line and the depth values.

- Calculate the effective stress using the overburden pressure and the pore pressure.

- Use the resistivity log to estimate the water saturation.

- Use the estimated water saturation and the effective stress to calculate the pore pressure using the Eaton equation.

4. Calculate the fracture gradient using the Eaton or Matthews-Kelly methods. These methods use different equations to estimate the fracture gradient based on the pore pressure and other well data. Here's an example of how to use the Eaton method:

- Calculate the minimum horizontal stress using the pore pressure, the density log, and the depth values.

- Calculate the maximum horizontal stress using the minimum horizontal stress and a stress ratio (which can be estimated based on the formation properties).

- Calculate the fracture gradient using the maximum horizontal stress and a safety factor (which can be based on the drilling conditions and the experience of the drillers).

5. Calculate the mud weight window by subtracting the pore pressure from the fracture gradient. This will give you the range of mud weights that can be safely used for drilling.

6. Visualize the data and results using graphs and charts. You can create plots of the well log data, the pore pressure, the fracture gradient, and the mud weight window to help you analyze the data and make decisions about drilling operations.

Note that these are just general steps and there may be other factors to consider depending on the specific well and formation being analyzed. It's also important to note that the accuracy of the estimates will depend on the quality and accuracy of the data used.

Hope it helps!!

Credit: mainly AI Tools

Bio pins

@sunil Bhat, with UTS, what do you mean?

Ahmed Merzoug

Thank you Dr. Ahmed

regards

EL-Mahdy

The best book that would suit your requirement is 'Fatigue of Materials' by Dr. Subra Suresh. The google book link is below:

Happy reading!

Spontaneous fracture of tempered glass due to nickel sulfide (NiS) inclusions is indeed a common issue. The phenomenon occurs as NiS undergoes a phase change from a high-temperature form (alpha-NiS) to a low-temperature form (beta-NiS), which causes an increase in volume and potentially induces enough stress to fracture the glass.

Now, regarding the fracture mirror: when a brittle material like glass fractures, it often produces certain characteristic features. These can include the mirror, mist, and hackle regions, which relate to the speed and direction of crack propagation. The mirror region, closest to the origin of the crack, is typically smooth and shiny, hence its name.

For NiS-induced fractures in tempered glass, a fracture mirror should theoretically be present around the NiS inclusion, which acts as the origin of the crack. However, it can indeed be very difficult to locate for several reasons:

Therefore, while a fracture mirror should be present in theory, it can often be very difficult to observe in practice. Methods like scanning electron microscopy (SEM) or other forms of microscopic analysis could potentially be used to locate and examine the fracture mirror if required.

You can try pressure washers for this, for example at a car wash. If that's not enough, then sandblasting with frozen CO2.

It looks like an Al-Si eutectic structure. It is brittle.

Hello, you can solve the problem using finite element software such as Abaqus. The two mentioned books recommended by friends are also good guides. You can also use other books on fracture mechanics.

I hope I have been able to help you.

Refer to the Mullins effect in elastomers and the phenomenon of creep. Study the variation of the internal energy of the bone as a function of strain By following these directions you will bring a completely new perspective to traumatology. This topic interests me. Let me know if you want to continue

You have to consider two scenarios, one as shallow aquifer and second as deeper aquifer. By measuring the depth to ground water in shallow aquifers and by constructing ground water table map, one can determine the gradient / direction of groundwater flow. However, when it comes to deeper aquifer mostly controlled by fractures, it is very difficult to determine the direction of groundwater flow. The fracture interconnection, fracture orientation, fracture gradient, there recharge zones, etc, makes this difficult. Like in the case of shallow aquifers, one can attempt to measure the depth to groundwater from borewells and construct groundwater maps, but they may not be the true representation of the fractured aquifer media.

Geophysical methods can indicate the presence of groundwater and to some extent their quality, but not the direction / orientation of groundwater flow.

Hello Dr Djandan Tadum Arthur Vithran

My opinion is that unfortunately there is currently no system of preventing fractures that is 100% successful.

To answer your questions:

BMD canNOT be regulated easily in the elderly population.

HRT modestly helps.

Vitamins do not really help (although the manufacturers/companies) make it sound good.

There are no drugs that are effective as far as I can tell or my friends who are geriatricians.

BMD studies (using DXA or any other method) are helpful only for checking]/monitoring but not able to help with treatment.

Thank you very much for your answer. I would also like to know whether the extended finite element in abaqus can be simulated when two or three natural fracture geometry parameters are known.

Thank you, Sumit Bhowmick, for pointing out the typo.

Dr. Govindarajan, greetings. If you are trying to characterize a reservoir with permeability anisotropy related to natural fractures, your biggest challenge is the inadequacy of borehole data to describe the fracture system. Several tasks must be undertaken to provide the context to extrapolate borehole data to the drainage area that would be sampled by dynamic well production data for history matching. The first task is to understand the relation of the reservoir-scale geologic structure to the regional stress field. Second, find suitable outcrop analogues to your reservoir based on what you know from the first task. Third, some attempt to develop a probabilistic geostatistical understanding of the fracture geometry and intensity at the reservoir scale from the outcrop analogue would help understand the range of uncertainty to apply to your wellbore data. The amount of uncertainty inherent in using just the wellbore data without a context to extrapolate it makes successful prediction difficult. John Lorenz has published data comparing vertical and horizontal cores that sampled fractured reservoirs. His work on the Multi-Well Experiment in Colorado would be a starting point.

Yes this is correct

The variation in analysis is so great that just about any model will work. The question (problem) is applying to say an acceptance tests with documented uncertainty for the values determined.

fractured schist can be source of water in movable or stored form but we can't say it is aquafer of unconfined , confined and semi - confined nature.

Hey Biswabhanu Puhan

Why not export (print) it as an .svg file? and then you can use Inkscape to do all sorts of things you need. I have tried with .svg format and it works perfectly for my model with Global Translucency Triggered.

Micro-cracks can form in the matrix zones of fiber reinforced polymer (FRP) composites for a variety of reasons. Some potential causes of micro-cracking in FRP composites include:

Micro-cracking in the matrix zones of FRP composites may be considered a defect, depending on the specific context and the severity of the cracks. In general, micro-cracking can affect the mechanical properties of the composite, such as its strength and stiffness, and may also affect its durability and service life.

Micro-cracks can also play a role in the initiation of fracture during the applied load. In general, micro-cracks can act as sites of stress concentration, and may promote the propagation of larger cracks when the composite is subjected to further loading. This can ultimately lead to failure of the composite material.

Dear Sophie,

I find your question really interesting, I hope my answer here will help you clarify a bit your doubts.

1. Yes, FFM is a two-parameter fracture criterion. In fact, Dölling & co-authors refer to the foundational paper of Leguillon ( ) on two-parameter (stress+energy) fracture criterion.

2. Yes, fracture processes are not modeled. Why? Because it's hard to do it. In terms of energy balance, the fracture problem involves external energy transferred macroscopically to the specimen that is dissipated by microscopic mechanisms at or very close to the crack tip. Thus, it is an inherently multi-scale problem. But we want to model it while staying in the realm of continuum (macroscopic) mechanics. Models like the cohesive zone model (cohesive elements) or phase field fracture mechanics try to model these dissipation mechanisms through internal variables and/or material properties, which have proven to be quite difficult to measure. In FFM, we simply assume that we can model the end result of these processes (i.e. macroscopic fracture) with a two-parameter macroscopic criterion. So, can you say something about these microscopic dissipative processes? Not really, as we are not modeling them. We assume that we can predict the end result by neglecting their exact physics and using a "correct" macroscopic criterion.

3. So, why the "Finite" in FFM? Well, it is so-called in comparison with what came before, i.e. Linear Elastic Fracture Mechanics (LEFM). Now, it is the latter name that is deceiving. The name LEFM is more historical than mathematical. Historically, first came elasticity, and upon the results of the theory of elasticity people like Irwin, Griffith, Westergaard built the foundations of what became Fracture Mechanics (FM). It was thus called LEFM. But if you look at the mathematical formulation of the fracture criteria proposed, it should be more properly called Infinitesimal Fracture Mechanics (IFM?). Why? Because the properties governing fracture (Stress Intensity Factors, Energy Release Rate, mode ratio, etc...) are evaluated in the limit r-->0 with r the radial distance from the crack tip, i.e. infinitesimally. In contrast, FFM starts from the assumption that fracture propagation is characterized by a finite length scale. Thus the properties governing fracture should not be evaluated infinitesimally, but at a finite "characteristic" distance from the crack tip. Thus the "finite" in FFM. How do you determine this characteristic distance? This is actually the problem in FFM, as the characteristic length is the main link between macroscopic criterion and microscopic dissipative processes. Usually, some calibration with experiments is needed to find a fitting value.

I hope it helps.

Best,

Luca

Plastazote has been proven in studies to reduce the chances of skin ulcerations in the diabetic population. In the United States, insurances typically do not cover diabetic insoles unless Plastazote is used as the top layer. In my practice, I typically use diabetic trilaminate for foot orthoses Plastazote top layer, PPT middle layer, and Cloud Crepe base layer), and Plastazote for Charcot Resistant Orthotic Walker (CROW) inserts.

Dear Amrit Raj Paul ,

you know that any height variation of the sample with respect to the optical center of the XRD system will shift the diffraction peaks a bit. So for a sufficiently rough or fractured surface you will get a peak broadening. This holds for metals and non-metallic material.

So as consequence any conclusions from peak broadening should be taken very carefully in such cases...

Best regards

G.M.

Hello, thank you for your interest. You wrote ""Almost all the articles I have seen about strain rate effects are descriptions or applications of the phenomenon, but I have not yet seen articles on the microphysical explanation of the existence of strain rate effects."". I felt the experience and the reflection covered by this sentence. It summarizes the heart of the problem because if the models of equation of state make it possible to answer; the experimental techniques, on the other hand, do not allow all the essential measurements to be carried out. Indeed, the measurements under shocks do not refer to the multiphonon processes, to the dielectric function and to the description of the energy processes under deformation. I will soon send you a link to the site dedicated to this research and to online training for materials experts. In the meantime, I am sending you a summary of the work.

Cordially.

Under thermal, mechanical, electrical, shock or irradiation stresses, insulators accumulate energy, age and explode; it is widely accepted that the microscopic mechanisms of these processes are not understood. However, it is shown that they arise from localized stresses around extensive defects and whose relaxation is at the origin of elastoplasticity and damage of materials. In metals, these defects are dislocations. In insulators, they are dislocations and traps for charge carriers, electrons or holes. The localized energy per defect depends on the permittivity of the medium, its mechanical moduli, the temperature and the losses. The energy, of the order of 10^4 to 10^6 eV /defect, is distributed over clusters of 10^4 to 10^6atoms. Its relaxation takes place in the characteristic time of the atomic polarization (10^(-9) s), that is to say at a very high deformation rate (10^8 s^(-1)), with the formation of shocks, followed by very strong increases of the temperature, of the electrical conductivity and of the polarization. The transfer by multiphonon processes of the relaxed energy to the neighboring bonds, is at the origin of the instabilities and the damages which result from it: bond breaking, aging, de-cohesion, formation of hot spots, crystallization of the amorphous parts, emission of particles, aging, progressive fracture and collective bond breaking process. Electron beam characterization uses traps to determine the maximum internal energy density that the material stably retains and to measure its decay when defects are destroyed. Knowing the initial state of the material, the measurements provide the envelope of the final states of the internal energy transformation. The initial state depends on the composition and manufacturing processes. The final state depends on the applied stresses. Therefore, one is able to develop defect engineering that involves modifying the elastoplastic characteristics of materials and ensuring that they are compatible with their operating constraints. This work includes a synthesis of testing and characterization techniques, a synthesis of the observations to be known when using these materials, a synthesis of the models that allowed us to know what to measure and how to do it, the principles of defect engineering, their application to various industrial problems.

Elena Shigorina

Granites normally develop fractures during cooling after emplacement. Additional fractures can be imposed by tectonic activity. It is likely that the cooling fractures will be symmetrical, but the tectonic fractures will be asymmetrical and perhaps sub-parallel. You might need to evaluate the fracture/joint orientation data before interpreting seismic data.

This is very intresting observations. What you defined as different fracture modes? There were static, quasi-static or dynamic loads?

The fracture pattern simply depends on the forces causing it. An angular force will cause transverse or short oblique fracture while rotating force will lead to long oblique or spiral fracture line. This can be seen by applying various combination of forces and the resultant fracture pattern in a chalk, used for writing on wall black boards.

Were you able to find a description of the variables required for the *fracture criterion? When I look through the manuals, I only find "useful" information in the form of "Data lines to specify the crack propagation criterion." For example, Abaqus analysis user's manual section 10.7.1. I can't seem to find anything that specifies the correct input form and details what each item is.

I think the correct form for the Paris law within the .inp file is something along the lines of,

*fracture criterion, type=fatigue,mixed mode behavior=power,

c_1, c_2, c_3, c_4, (G_thresh/G_c), (G_pl/G_c), G_1, G_2, G_3, a_m,a_n, a_0

However, I can not find a way to verify this. Are you aware of any? From what I can tell, Abaqus fails to include information on how to apply anything in the manuals to the actual program.

Independent of which material model you take, you need to provide information on the hardening behavior in the post-necking regime in order to be able to simulate this region. Getting this information for a real material from experiments is not trivial. Though, there are established methods to extract true-stress vs. true strain data from the post-necking regime, e.g. using Bridgeman's correction or doing an inverse parameter identification (the latter is necessary definiely in case of complex stress states). A pragmatic approach is that you take the true pre-necking data and extrapolate them to the post-necking regime using an analytical law like a power law or a Voce law. Subsequently, the analytical law can be either rasterized to obtain the tabulated data for the built-in plasticity models of Abaqus or you implement it as a user-defined hardening law using the UHARD routine. Our GTN implementation (open source at https://tu-freiberg.de/nonlocalGTN ) supports power-law hardening by default.

I advise You to look at pages 48 and 49 of the attached PDF file, but You will have to translate the text from Russian.

Hello Sharon Pc did you resolve this problem? thanks

dear sir, you may get answer here

A3 and a4 fractures in neuro intact patients may be classified as B2 injuries and change initial treatment. I think for A3 and A4 when considering non operative management an Mri is highly recommended.

Hi, you don't need any special equipment. We don't use it in our lab either. But it is easier to buy a DCPD. On the other hand, you are a little proud when the system finally runs. :)

We use a nanovoltmeter and a PC with a self-written software in Labview.

You have to measure on your sample the voltage drop at your crack ("active signal") and the voltage at a spot without crack ("reference signal"). In addition, total voltage and total current.

We do the evaluation with Matlab. In the standards, you will find the corresponding formulas for the ratio of electrical voltage to crack length.

I recommend the insertion of striations during the crack propagation test for a better correlation of the crack length. A reference test may be necessary.

Regards,

Michael

You can compare 2 different technics Prof. Dr.Marwan Mutib

Refraction seismic & Reflection seismic. I guess refraction helps more to identify the closest to the surface type of lithology and water reservoirs, I guess.

Please take a look at the following link, quite instructive:

Best Regards.