As of Thursday I have completed all required safety training for any individual working in a lab. This blog will be rather short as most of last week was spent preparing for the training.
Prior to receiving the necessary lab safety training, I not able to be a hands-on participant in any of the experimentation being preformed in the lab. Now that I have completed all three required courses (Fire-safety, Hazardous waste management, and General Lab safety) I am able to help Luca, Himai, and Jacob during testing.
Each lab safety course essentially preaches the same overarching idea : Mistakes happen when you are not diligent and acting with a purpose. Which translates to: Have common sense, the machines your working with can kill you so treat it with respect. Once I let that idea sink in, being careful in the lab no longer seemed to be some kind of drag or nuisance, but rather a means to improve your testing experience and the quality of your results.
My next blog post will contain my experiences from interning as well as anything that was done in the lab.
Thanks for reading,
Nick Thompson
Wednesday, March 22, 2017
Monday, March 20, 2017
Cutting Nylon Samples with a side of Stress and Strain Analysis
This blog post will pertain to my first day interning post-ASU spring break as well as things to come in the next couple days.
Until I receive my lab safety course on the 16th of March, I am essentially a bi-stander during the whole experimentation portion of the project. During my time at ASU, I have been helping anyone who needs a hand with something as well as furthering my understanding of stress and strain by reading the Mechanics of Materials textbook.
On Wednesday, March 15th, I helped Luca Alfarano cut some nylon samples which will be used for testing in the coming days.
Things have been at a rather slow pace as Dr. Mobasher awaits the arrival of some NASA provided nylon samples, which are of the exact specifications of the parachutes NASA is using.
My next blog post will be about my lab safety course and ways I will be able to contribute to project in the coming weeks.
Thanks for reading,
Nick Thompson
Monday, March 6, 2017
This blog post will talk about my internship experiences on Thursday and Friday of last week at ASU.
Thursday 03/02/2017:
I went to ASU on Thursday to help Luca Alfarano prepare nylon samples he would be testing on Friday and Saturday. Unfortunately, since ASU is on Spring break next week, I will not be able to provide "hands-on" help in the lab and will just be an observer to the experiments.
Dr. Mobasher provided me with several links as a means to become more familiar with the entire project as a whole. The nylon testing that Dr. Mobasher and his team are preforming at ASU is only a portion of the actual NASA LDSD project. LDSD stands for "Low-Density Supersonic Decelerator" and is currently being worked on by scientists and engineers at NASA and JPL.
I will provide the links at the end of this blog post for anyone that is interested in watching the videos.
Friday 03/03/2017:
On Friday I helped Luca prepare more samples of nylon for testing he would be doing later in the day.
The entire process of preparing the samples is incredibly repetitive and meticulous.
Preparing the Nylon Samples:
The first step in the sample preparation is to cut the aluminium sheet into rows with a width of 1.6"
Next, cut the rows into sections that are 2.1" in length. (each section will be used as a grip for the nylon same and each nylon sample uses 4 grips)
Once the aluminium sections are cut, the gage length must be marked on the sample of nylon for proper placement of the aluminium grips. The gage length is the part of the nylon which will be tested.
Next, apply super glue to one side of an aluminium grip and place on the nylon. Two grips will be placed on the bottom of the nylon sample and two will be placed on top of the nylon sample, one directly onto each of bottom grips.
Before testing the sample, paint must be applied in a very tedious process in order for DIC to properly detect deformation in the sample during testing.
ASU is on Spring break next week so my hours will partly spent in the lab and partly spent at BASIS Phoenix. However, I plan to continue my independent reading of my Mechanics of Materials textbook as well as readings for my project.
Links:
https://www.youtube.com/watch?
https://www.youtube.com/watch?
https://www.youtube.com/watch?
https://www.youtube.com/watch?
https://www.youtube.com/watch?
Thanks for reading,
-Nick Thompson
Thursday 03/02/2017:
I went to ASU on Thursday to help Luca Alfarano prepare nylon samples he would be testing on Friday and Saturday. Unfortunately, since ASU is on Spring break next week, I will not be able to provide "hands-on" help in the lab and will just be an observer to the experiments.
Dr. Mobasher provided me with several links as a means to become more familiar with the entire project as a whole. The nylon testing that Dr. Mobasher and his team are preforming at ASU is only a portion of the actual NASA LDSD project. LDSD stands for "Low-Density Supersonic Decelerator" and is currently being worked on by scientists and engineers at NASA and JPL.
I will provide the links at the end of this blog post for anyone that is interested in watching the videos.
Friday 03/03/2017:
On Friday I helped Luca prepare more samples of nylon for testing he would be doing later in the day.
The entire process of preparing the samples is incredibly repetitive and meticulous.
Preparing the Nylon Samples:
The first step in the sample preparation is to cut the aluminium sheet into rows with a width of 1.6"
Next, cut the rows into sections that are 2.1" in length. (each section will be used as a grip for the nylon same and each nylon sample uses 4 grips)
Once the aluminium sections are cut, the gage length must be marked on the sample of nylon for proper placement of the aluminium grips. The gage length is the part of the nylon which will be tested.
Next, apply super glue to one side of an aluminium grip and place on the nylon. Two grips will be placed on the bottom of the nylon sample and two will be placed on top of the nylon sample, one directly onto each of bottom grips.
Before testing the sample, paint must be applied in a very tedious process in order for DIC to properly detect deformation in the sample during testing.
ASU is on Spring break next week so my hours will partly spent in the lab and partly spent at BASIS Phoenix. However, I plan to continue my independent reading of my Mechanics of Materials textbook as well as readings for my project.
Links:
https://www.youtube.com/watch?
https://www.youtube.com/watch?
https://www.youtube.com/watch?
https://www.youtube.com/watch?
https://www.youtube.com/watch?
Thanks for reading,
-Nick Thompson
Thursday, March 2, 2017
My First Few Days at ASU
I started my internship with Dr. Mobasher at ASU on Tuesday of this week. Dr. Mobasher put me into contact with three of his post-graduate students: Jacob Bauchmoyer, Himai Mehere, and Luca Alfarano. Jacob and Himai are both obtaining their Masters degree from ASU in Civil Engineering and Luca is on a six-month research exchange program from Italy.
Day 1 02/28/17:
After introducing myself to Jacob, Himai, and Luca, I was given a tour of the laboratory which Dr. Mobasher and his team use for experimentation. I was shown the INSTRON machine which uses a constant strain rate to cause a displacement at one end of the nylon sample being used in testing. Displacement of the nylon introduces uniaxial stress into the material and eventually causes deformation in the nylon structure.
Once we returned from the lab, I was also introduced to Digital Image Correlation, or DIC in short. The DIC method takes and uses photographs, which are taken in constant time intervals during the experiment, to digitally analyze and measure deformation of the sample being used until failure.
The tedious process of setting up the DIC cameras and preparing the nylon samples according to the proper guidelines can take several hours, while the actual tests only last for about 20 minutes. Reminds me of playing with dominos...you spend an hour or more setting them up and then watch them fall for the best 10-15 seconds of your life.
Later in the day I was assigned more reading in the Mechanics of Materials textbook by Dr. Mobasher. I read through sections 7.1, 7.2, and 7.3 and took notes on those sections.
Day 2 03/01/17:
I started my day with continuing my reading of Chapter 7, finishing section 7.4 and 7.5.
In order to be in the lab while experimentation is ongoing, I must take three ASU required lab safety courses. Jeff Long, the Laboratory Manager for the Ira A. Fulton School of Engineering, helped me register for the Hazardous waste management and Fire safety and Prevention courses, which are taught online, and another course about Lab Safety, which is taught in a classroom. The two online courses required me to listen to an audio presentation about each subject and take an exam which required a minimum score of 87% to pass the class. I was able to finish both online courses while at ASU on Wednesday, but I will not be able to take the in-class Lab safety course until March 16th, because of Spring break. Therefore I will not be able to help with any tests until I have completed that course.
My post tomorrow will contain my experience on my third day of interning as well as my plan for next week.
Thanks for reading,
-Nick Thompson
Day 1 02/28/17:
After introducing myself to Jacob, Himai, and Luca, I was given a tour of the laboratory which Dr. Mobasher and his team use for experimentation. I was shown the INSTRON machine which uses a constant strain rate to cause a displacement at one end of the nylon sample being used in testing. Displacement of the nylon introduces uniaxial stress into the material and eventually causes deformation in the nylon structure.
Once we returned from the lab, I was also introduced to Digital Image Correlation, or DIC in short. The DIC method takes and uses photographs, which are taken in constant time intervals during the experiment, to digitally analyze and measure deformation of the sample being used until failure.
The tedious process of setting up the DIC cameras and preparing the nylon samples according to the proper guidelines can take several hours, while the actual tests only last for about 20 minutes. Reminds me of playing with dominos...you spend an hour or more setting them up and then watch them fall for the best 10-15 seconds of your life.
Later in the day I was assigned more reading in the Mechanics of Materials textbook by Dr. Mobasher. I read through sections 7.1, 7.2, and 7.3 and took notes on those sections.
Day 2 03/01/17:
I started my day with continuing my reading of Chapter 7, finishing section 7.4 and 7.5.
In order to be in the lab while experimentation is ongoing, I must take three ASU required lab safety courses. Jeff Long, the Laboratory Manager for the Ira A. Fulton School of Engineering, helped me register for the Hazardous waste management and Fire safety and Prevention courses, which are taught online, and another course about Lab Safety, which is taught in a classroom. The two online courses required me to listen to an audio presentation about each subject and take an exam which required a minimum score of 87% to pass the class. I was able to finish both online courses while at ASU on Wednesday, but I will not be able to take the in-class Lab safety course until March 16th, because of Spring break. Therefore I will not be able to help with any tests until I have completed that course.
My post tomorrow will contain my experience on my third day of interning as well as my plan for next week.
Thanks for reading,
-Nick Thompson
Sunday, February 26, 2017
Final Notes on Chapter 2. Sections 2.10, 2.11, 2.12
This blog post will contain my notes from the final sections of chapter 2.
2.10: Stress Concentrations
Stress concentrations: High stresses in very small regions of a bar.
Stress Concentration Factors:
The intensity of a stress concentration is usually determined by the ratio between maximum stress and normal stress, this is depicted by the stress-concentration factor K: \[K = \frac{{{\sigma _{\max }}}}{{{\sigma _{nom}}}}\] \({\sigma _{nom}} = \frac{P}{{ct}}\) = nominal stress (where ct is the net area at the cross section of the hole.)
2.11: Nonlinear Behavior
Perfect Plasticity: perfectly plastic regions on a stress-strain curve continue until the strains are 10 or 20 times larger than the yield strain.
A material having a stress-strain diagram with theses types of characteristics is called an elastoplastic material.
2.12: Elastoplastic Analysis
Yield displacement is the downright displacement of the bar at the yield load and is equal to the elongation of the inner bar when first releasing yield stress \({\sigma _y}\) :\[{\delta _Y} = \frac{{{\sigma _y}{L_2}}}{E}\] The plastic displacement \({\delta _Y}\) at the instant the load just reaches the plastic load \({P_p}\) and is equal to the elongation of the outer bars at the instant they reach yield stress.
\[{\delta _P} = \frac{{{\sigma _y}{L_1}}}{E}\] Now Compare \({\delta _P}\) with \({\delta _y}\) and get the ratio: \[\frac{{{\delta _P}}}{{{\delta _y}}} = \frac{{{L_1}}}{{{L_2}}}\] My next blog posts will be about my first few days at my internship and some of the interesting and new experiences I will have had working in a lab.
Thanks for reading,
-Nick Thompson
2.10: Stress Concentrations
Stress concentrations: High stresses in very small regions of a bar.
Stress Concentration Factors:
The intensity of a stress concentration is usually determined by the ratio between maximum stress and normal stress, this is depicted by the stress-concentration factor K: \[K = \frac{{{\sigma _{\max }}}}{{{\sigma _{nom}}}}\] \({\sigma _{nom}} = \frac{P}{{ct}}\) = nominal stress (where ct is the net area at the cross section of the hole.)
2.11: Nonlinear Behavior
Perfect Plasticity: perfectly plastic regions on a stress-strain curve continue until the strains are 10 or 20 times larger than the yield strain.
A material having a stress-strain diagram with theses types of characteristics is called an elastoplastic material.
2.12: Elastoplastic Analysis
Yield displacement is the downright displacement of the bar at the yield load and is equal to the elongation of the inner bar when first releasing yield stress \({\sigma _y}\) :\[{\delta _Y} = \frac{{{\sigma _y}{L_2}}}{E}\] The plastic displacement \({\delta _Y}\) at the instant the load just reaches the plastic load \({P_p}\) and is equal to the elongation of the outer bars at the instant they reach yield stress.
\[{\delta _P} = \frac{{{\sigma _y}{L_1}}}{E}\] Now Compare \({\delta _P}\) with \({\delta _y}\) and get the ratio: \[\frac{{{\delta _P}}}{{{\delta _y}}} = \frac{{{L_1}}}{{{L_2}}}\] My next blog posts will be about my first few days at my internship and some of the interesting and new experiences I will have had working in a lab.
Thanks for reading,
-Nick Thompson
Notes on Sections 2.6, 2.7, and 2.8 in Chapter 2
This blog post is a continuation of my notes of Chapter 2 and will contain sections 2.6, 2.7, 2.8.
2.6: Stress on Inclined Sections
Stress Elements:
A stress element is an isolated element of a material which depicts the stresses acting on all faces of that elements.
The dimensions of a stress element are assumed to be infinitesimally small and are therefore drawn to a large scale.
Stresses on Inclined Sections:
Observing the stresses acting on inclined section of an object provides a more complete picture. Since the stresses are uniform throughout the entire bar, the stresses acting over the inclined section must be equally distributed.
When observing the inclined section of an object, you must first specify the orientation of the inclined section. Orientation is usually established by the angle \(\theta \) between the x-axis and the normal to the section.
To find the stresses acting on a section, the forces must be broken up into components. These components are the normal force N and shear force V, which is tangential to the plant of the object. The force components can be expressed as:
Since \({\sigma _\theta } = \frac{N}{{{A_1}}} = \frac{P}{A}{\cos ^2}\theta \) and \({\tau _\theta } = - \frac{V}{{{A_1}}} = - \frac{P}{A}\sin \theta \cos \theta \)
The normal and shear stresses can be defined as:
\({\sigma _\theta } = {\sigma _x}{\cos ^2}\theta = {\sigma _x}(1 + \cos 2\theta )\)
\({\tau _\theta } = - {\sigma _x}\sin \theta \cos \theta = - \frac{{{\sigma _x}}}{2}(\sin 2\theta )\)
Maximum Normal and Shear Stresses:
\({\sigma_\theta } = {\sigma_x}\) when \({\theta} = 0\)
As \({\theta }\) increases or decreases, the normal stress diminishes until \({\theta }\) = \(\pm \) \({90^ \circ }\) where it becomes zero, because there are no normal stresses on sections parallel to the longitudinal axis. The maximum normal stress occurs at \({\theta }\) = 0 and is: \[{\sigma_{max}} = {\sigma_x}\]
When \({\theta }\) = \(\pm \) \({45^ \circ }\), the normal stress is one half the maximum value.
The maximum shear stresses have the same magnitude:
2.7: Strain Energy
2.7 looks at strain energy from its simplest form , through axially loaded members subjected to static loads. A static load is one that has no dynamic or inertial effects due to motion.
Loads can be classified as static or dynamic depending on whether they remain constant or vary with time.
-A static load is applied slowly so it causes no vibrational or dynamic effects in the structure.
-Dynamic loads take many forms - some are apllied and removed suddenly (impact loads), others persist for long periods of time and continuously vary in intensity (fluctuating loads)
Maximum elongation of the Bar:
Starting by equating the potential energy lost to maximum strain energy, we may get to maximum elongation of a bar with several derivations.
Our starting equation:
\[w(h + {\delta _{\max }}) = \frac{{EA{\delta _{\max }}}}{{2L}}\]
And max elongation is found to be :
\[{\delta _{\max }} = \sqrt {2h{\delta _{st}}} = \sqrt {\frac{{m{v^2}L}}{{EA}}} \]
Maximum Stress in a Bar:
\[{\sigma _{\max }} = \frac{{E{\delta _{\max }}}}{L}\]
Through several derivations and substitutions, we arrive at the final equation which describes the maximum stress which a bar can receive:
\[{\sigma _{\max }} = \sqrt {\frac{{m{v^2}E}}{{AL}}} \]
Impact Factor:
The Impact factor is known as the ratio between the dynamic response of a structure and the static response (for the same load) :
Impact Factor = \( \frac{{{\delta _{\max }}}}{{{\delta _{st}}}}\)
My next blog post will be on my notes on the final sections of Chapter 2. Sections 2.10, 2.11, and 2.12.
Thanks for reading,
-Nick Thompson
2.6: Stress on Inclined Sections
Stress Elements:
A stress element is an isolated element of a material which depicts the stresses acting on all faces of that elements.
The dimensions of a stress element are assumed to be infinitesimally small and are therefore drawn to a large scale.
Stresses on Inclined Sections:
Observing the stresses acting on inclined section of an object provides a more complete picture. Since the stresses are uniform throughout the entire bar, the stresses acting over the inclined section must be equally distributed.
When observing the inclined section of an object, you must first specify the orientation of the inclined section. Orientation is usually established by the angle \(\theta \) between the x-axis and the normal to the section.
To find the stresses acting on a section, the forces must be broken up into components. These components are the normal force N and shear force V, which is tangential to the plant of the object. The force components can be expressed as:
\(N = P\cos \theta \) \(V = P\sin\theta\)
Since \({\sigma _\theta } = \frac{N}{{{A_1}}} = \frac{P}{A}{\cos ^2}\theta \) and \({\tau _\theta } = - \frac{V}{{{A_1}}} = - \frac{P}{A}\sin \theta \cos \theta \)
The normal and shear stresses can be defined as:
\({\sigma _\theta } = {\sigma _x}{\cos ^2}\theta = {\sigma _x}(1 + \cos 2\theta )\)
\({\tau _\theta } = - {\sigma _x}\sin \theta \cos \theta = - \frac{{{\sigma _x}}}{2}(\sin 2\theta )\)
Maximum Normal and Shear Stresses:
\({\sigma_\theta } = {\sigma_x}\) when \({\theta} = 0\)
As \({\theta }\) increases or decreases, the normal stress diminishes until \({\theta }\) = \(\pm \) \({90^ \circ }\) where it becomes zero, because there are no normal stresses on sections parallel to the longitudinal axis. The maximum normal stress occurs at \({\theta }\) = 0 and is: \[{\sigma_{max}} = {\sigma_x}\]
When \({\theta }\) = \(\pm \) \({45^ \circ }\), the normal stress is one half the maximum value.
The maximum shear stresses have the same magnitude:
\({\tau _{\max }} = \frac{{{\sigma _x}}}{2}\)
2.7: Strain Energy
2.7 looks at strain energy from its simplest form , through axially loaded members subjected to static loads. A static load is one that has no dynamic or inertial effects due to motion.
Work is therefore defined as: \[W = \int\limits_0^\delta {{P_1}d{\delta _1}} \]
Strain energy is equal to work so it is therefore equal to the work equation stated above.
Elastic and Inelastic Strain Energy:
Elastic strain energy is strain energy recovered during unloading.
Inelastic strain energy is strain energy that is permanently lost during the unloading process.
Linearly Elastic Behavior:
\[U = W = \frac{{P\delta }}{2}\]
This equation describes the strain energy, U, stored in a bar
Since \(\delta = \frac{{{P^2}L}}{{2EA}}\), in a linearly elastic bar strain energy can take either of the following forms:
\(U = \frac{{{P^2}L}}{{2EA}}\) or \(U = \frac{{EA{\delta ^2}}}{{2L}}\)
Displacements caused by a single load:
Since U = W = \(\frac{{P\delta}}{2}\), this questions can be easily rearranged to solve for displacement:
\[\delta = \frac{{2U}}{P}\]
2.8: Impact Loading
Loads can be classified as static or dynamic depending on whether they remain constant or vary with time.
-A static load is applied slowly so it causes no vibrational or dynamic effects in the structure.
-Dynamic loads take many forms - some are apllied and removed suddenly (impact loads), others persist for long periods of time and continuously vary in intensity (fluctuating loads)
Maximum elongation of the Bar:
Starting by equating the potential energy lost to maximum strain energy, we may get to maximum elongation of a bar with several derivations.
Our starting equation:
\[w(h + {\delta _{\max }}) = \frac{{EA{\delta _{\max }}}}{{2L}}\]
And max elongation is found to be :
\[{\delta _{\max }} = \sqrt {2h{\delta _{st}}} = \sqrt {\frac{{m{v^2}L}}{{EA}}} \]
Maximum Stress in a Bar:
\[{\sigma _{\max }} = \frac{{E{\delta _{\max }}}}{L}\]
Through several derivations and substitutions, we arrive at the final equation which describes the maximum stress which a bar can receive:
\[{\sigma _{\max }} = \sqrt {\frac{{m{v^2}E}}{{AL}}} \]
Impact Factor:
The Impact factor is known as the ratio between the dynamic response of a structure and the static response (for the same load) :
Impact Factor = \( \frac{{{\delta _{\max }}}}{{{\delta _{st}}}}\)
My next blog post will be on my notes on the final sections of Chapter 2. Sections 2.10, 2.11, and 2.12.
Thanks for reading,
-Nick Thompson
Thursday, February 23, 2017
Notes on Chapter 2 Sections 2.3, 2.4, 2.5
Towards the end of last week I finished reading sections 2.3 through 2.5 in Chapter 2. This post will give a summary of the important topics through those specific sections.
2.3 :
Section 2.3 dealt with changing material lengths under nonuniform conditions.
When a linearly elastic material is loaded only at the ends, the change in length of the material can be obtained through the equation:
2.3 :
Section 2.3 dealt with changing material lengths under nonuniform conditions.
When a linearly elastic material is loaded only at the ends, the change in length of the material can be obtained through the equation:
\(\partial = \frac{{PL}}{{EA}}\)
Where P is the load on the bar, L is the length of the bar, E is the modulus of elasticity, and A is the cross sectional are.
However, 2.3 deals with this equation in a more general sense and not just solely when it is used for linearly elastic materials.
Bars consisting of Prismatic Segments:
The change in length of the bar when loaded can be obtained from the equation:
\(\partial = \sum\limits_{i = 1}^n {\frac{{{N_i}{L_i}}}{{{E_i}{A_i}}}} \)
Where i is the numbering index for various segments, n is the total number of segments, and \({{N_i}}\) is the internal axial force in segment i.
Bars with continuously Varying Loads or Dimensions:
Given that: \[d\partial = \frac{{N(x)dx}}{{EA(x)}}\]
The elongation of the entire bar is obtained by integrating over the entire length with respect to x.
\[\partial = \int\limits_0^L {d\partial = \int\limits_0^L {\frac{{N(x)dx}}{{EA(x)}}} } \]
2.4 :
Section 2.4 deals with statically indeterminate structures.
A structure is classified as statically determinate if its reactions and internal forces can be determined solely from free-body diagrams and equations of equilibrium (i.e \(\sum F = 0\)). It is important to note that the forces of statically determinate structures can be found without knowing the properties of the materials.
However, most structures are more complex that a bar and their reactions and internal forces cannot be found by statics alone. These types of structures are classified as statically indeterminate. In order to analyze these structures, supplemental equations must be used in addition to displacement equations.
2.5 :
Sections 2.5 deals with Thermal effects, Misfits, and Prestrains.
External loads are not the only sources of stresses and strains in a structure. Other sources include thermal effects, which arise from temperature changes, misfits, which result from imperfections in construction, and prestrains, produced by initial deformations.
Thermal effects:
Changes in temperature produce expansion or contraction of structural materials, resulting in thermal strains and thermal stresses.
The equation for thermal strain \({\varepsilon _T}\) is proportional to the temperature change \(\Delta T\):
\[{\varepsilon _T} = \alpha (\Delta T)\]
Where \(\alpha\) is the coefficient of thermal expansion.
Temperature-displacement relation calculates the increase in any dimension by the equation:
\[\partial ={ \varepsilon_T}L= \alpha(\Delta T)L\]
Misfits:
Misfit members are members with slightly different measurements than those which were intended in their design and consequently do not fit properly in their structure.
Prestrains:
Prestrains occur in a system when misfit members are used in construction of a given structure. These misfit members introduce strains and stresses into the structure before any loads are applied to it and are therefore called "Prestrains" and "Prestresses."
If a structure is statically determinate, small misfits in one or more members will not produce strains or stresses in the overall structure. However, in statically indeterminate structures, small misfits do introduce strains and stresses as the overall structure is not free to adjust to those misfit members.
Next post will pertain to my notes on sections 2.6, 2.7, 2.8, and 2.9.
Thanks for reading,
-Nick Thompson
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