In brittle materials the ultimate tensile strength is close to the yield pointwhereas in ductile materials the ultimate tensile strength can be higher. The ultimate tensile strength is usually found by performing a tensile test and recording the engineering stress versus strain.
The highest point of the stress—strain curve is the ultimate tensile strength and has units of stress. Tensile strengths are rarely used in the design of ductile members, but they are important in brittle members.
They are tabulated for common materials such as alloyscomposite materialsceramicsplastics, and wood. The ultimate tensile strength of a material is an intensive property ; therefore its value does not depend on the size of the test specimen. However, depending on american standard toilet colors in 1960s material, it may be dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material.
Some materials break very sharply, without plastic deformationin what is called a brittle failure. Others, which are more ductile, including most metals, experience some plastic deformation and possibly necking before fracture. Tensile strength is defined as a stress, which is measured as force per unit area. For some non-homogeneous materials or for assembled components it can be reported just as a force or as a force per unit width.
Many materials can display linear elastic behaviordefined by a linear stress—strain relationshipas shown in figure 1 up to point 3. The elastic behavior of materials often extends into a non-linear region, represented in figure 1 by point 2 the "yield point"up to which deformations are completely recoverable upon removal of the load; that is, a specimen loaded elastically in tension will elongate, but will return to its original shape and size when unloaded.
Beyond this elastic region, for ductile materials, such as steel, deformations are plastic. A plastically deformed specimen does not completely return to its original size and shape when unloaded. For many applications, plastic deformation is unacceptable, and is used as the design limitation. After the yield point, ductile metals undergo a period of strain hardening, in which the stress increases again with increasing strain, and they begin to neckas the cross-sectional area of the specimen decreases due to plastic flow.
In a sufficiently ductile material, when necking becomes substantial, it causes a reversal of the engineering stress—strain curve curve A, figure 2 ; this is because the engineering stress is calculated assuming the original cross-sectional area before necking. The reversal point is the maximum stress on the engineering stress—strain curve, and the engineering stress coordinate of this point is the ultimate tensile strength, given by point 1. It is, however, used for quality control, because of the ease of testing.
It is also used to roughly determine material types for unknown samples. The ultimate tensile strength is a common engineering parameter to design members made of brittle material because such materials have no yield point. Typically, the testing involves taking a small sample with a fixed cross-sectional area, and then pulling it with a tensometer at a constant strain change in gauge length divided by initial gauge length rate until the sample breaks.
When testing some metals, indentation hardness correlates linearly with tensile strength. This important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers.
From Wikipedia, the free encyclopedia. Redirected from Ultimate strength. Main article: Tensile testing. Archived from the original on 1 December Retrieved 27 April Archived from the original on 16 February Retrieved 20 February Nitinol is an alloy that will remember a shape you select, and whenever you heat it to a certain temperature called the transistion temperatureit will automatically go back to the remembered shape.
Below are things I've made using nitinol wire along with some tips I've learned along the way. A simple first experiment was to bend nitinol wire around some nails into the shape of a letter R. I then heated it using a candle flame to above C F while still held in the shape of an R.
I next quickly dipped it cool water. After that the shape is remembered by the wire. I next straightened out the wire and then quickly put it in the candle flame again in order to get it to the transistion temperature. It went back to the remembered shape of the letter R. I wanted to test how much force it could produce when heated back to its remembered shape. To heat it to its transition temperature I ran electric current through it with the setup shown below. The nitinol spring was hung, stretched out, from a spring balance and the current was measured on a meter.
A potentimeter was connected in series with the circuit to help limit the current. As the current was turned up and reached 0. In doing so, it pulled down on the spring balance as much as it could. The balance showed 27 grams. As a fun project I made an inchworm using a nitinol wire coil to make it walk across a table. I purchased the wire that I demonstrate above by shaping into an R and that I shape into a spring below from Kellogg's Research Labs. It is 0. According to their forum, to set the wire's shape into it's memory you heat it to C F.
Also, according the the specs for the one I bought, the transistion temperature at which it restores itself back to its remembered shape is 70C F. But I couldn't get it to go back to its remembered shape even by putting it in hot water up to C F.
Instead I had to put it in a much hotter candle flame or run electrical current through it, producing a higher temperature.
My guess is that at some point I had unknowingly raised the transistion temperature. Again, according to Kellogg's forum, heating this wire to C F will raise the transistion temperature. My guess is I'd done that by leaving it in the candle flame sometimes for too short a time when trying to set the shape. It's also possible I'd sufficiently heated part of the wire to set the shape but since I hadn't cut that part from the rest of my wire, the section of wire next to it got heated to a lower temperature around C Fraising the transistion temperature for that section.
When I later went to use that section, it had a higher than expected transistion temperature. Since I didn't know the new transistion temperature for my wire, I sometimes used a candle flame to get it to go back to its programmed shape. If I left it too long in the flame then its temperature sometimes went as high at the required C F to set a new shape. The remembered shape changed to whatever shape it happened to be in at the time. So again, good temperature control helps.
For my spring experiments, at least by using electrical current to get it to go back to its programmed shape, and since I had control of the current using my power supply and potentiometer, I had some control of the temperature that way.
In the following video I start with the demonstration of making the letter R and then follow that with making the spring and measuring the force as the spring restores its shape using electric current to produce the heat. Nitinol wire shape memory alloy - experiments and devices. Simple experiment - the letter "R" for Rimstar. Bent in the shape of an "R".
Heating above C F.Introduction to Nitinol A comprehensive guide to Nitinol is available for download. This document provides the information required for a solid technical understanding of concepts ranging from metallurgy and the effects on physical properties to ideal component manufacturing technologies and common quality control testing methods.
Download PDF. Nitinol IQ Over the years, as a leader in Nitinol manufacturing, our team at Memry has accumulated a vast amount of metallurgical and component processing knowledge. As a company, Memry is dedicated to making your job easier by disseminating our knowledge in Nitinol through the publication of technical content.
History Nitinol is a nickel-titanium alloy distinguished from other materials by its shape memory and superelastic characteristics. A team from the NOL discovered the alloy while searching for materials that could be used in tools for dismantling magnetic mines. At the time, Goodyear Aerospace Corp. Beyond these early predictions, Nitinol has proved to be widely useful in the medical device arena. Engineers have used it for devices that maintain blood flow within an artery, implants that restore function to a failing heart valve and retrieval devices that remove life threatening blood clots from deep within the brain.
You can learn more about Nitinol from our Memry white papers. Nitinol Glossary The following technical terms and their definitions are essential for understanding Nitinol and the concepts presented in this document. Active austenite finish temperature Active Af — term for austenite finish temperature of raw wire, tube, sheet or semi-finished component as determined by bend and free recovery BFR test method described in ASTM F The active Af is often preferred when specifying thermal properties of a component as it is more representative of performance in application.
Austenite — the high temperature parent phase of the Nitinol alloy having a B2 crystal structure.
Austenite finish temperature Af — the temperature at which martensite or R-phase to austenite transformation is completed on heating of the alloy. Austenite peak temperature Ap — the temperature of the endothermic peak position on the differential scanning calorimetry DSC curve upon heating for the martensite or R-phase to austenite transformation. Austenite start temperature As — the temperature at which the martensite or R-phase to austenite transformation begins on heating of the alloy.
Free recovery — unconstrained motion of a shape memory alloy upon heating and transformation to austenite after deformation in a lower temperature phase. Martensite deformation temperature Md — the highest temperature at which martensite will form from the austenite phase in response to an applied stress.
At temperature above Md the Nitinol shape memory alloy will not exhibit superelasticity it will rather exhibit a typical elastic-plastic behavior when loaded. Martensite finish temperature Mf — the temperature at which the transformation of martensite from austenite or R-phase is completed on cooling of the alloy. Martensite peak temperature Mp — the temperature of the exothermic peak position on the DSC curve upon cooling for the austenite or R-phase to martensite transformation.
Martensite start temperature Ms — the temperature at which the transformation from austenite or R-phase to martensite begins on cooling of the alloy.
Pseudoelasticity — another name for superelasticity. See superelasticity. R-phase — the intermediate phase which may form between austenite and martensite. The R-phase occurs in Nitinol alloys under certain conditions. The R-phase has a rhombohedral crystal structure. R-phase finish temperature Rf — the temperature at which the transformation from austenite to R-phase is completed on cooling; in an alloy that exhibits two-stage transformation.
R-phase peak temperature Rp — the temperature of the exothermic peak position on the DSC curve upon cooling for the austenite to R-phase transformation. R-phase start temperature Rs — the temperature at which the transformation from austenite to R-phase begins on cooling; in an alloy that exhibits two-stage transformation. Superelasticity — nonlinear recoverable deformation behavior of Nitinol shape memory alloys that occurs at temperatures above Af but below Md.All of the actuators below can be used to actuate solenoids.
An SMA powered solenoid can be many times smaller and lighter than an elecotro-magnet powered solenoid. SMA powered solenoids will also use a small fraction of the power. Solenoids are much heavier than nitinol actuators for comparable force output.
All of which are possible with nitinol actuators. There is a U-shaped Nitinol wire actuator on each side of the PCB only one is currently installedand they operate on a shared linkage.
The SMA wire used here was 0. An embedded coil, 12 layer spiral as shown, can be used to move a magnet which could be used to create a very small solid state pump for air or liquid or valve system arrays. Using standard printed circuit board PCB more than 1, of such devices can be printed This demonstrated the ability to operate in water and shows that the water cools the device enough to operate at high speed and high force. This is a high force linear actuator with a single SMA wire wound around pulleys to provide high force.
This long stroke, high speed, prototype SMA actuator was designed for Sony to remove DVD's that did not pass quality control from an assembly line. Mineral oil is used in the body of this actuator to enhance cooling of the Nitinol. This actuator features 8" of 0. This video illustrates how a thin film force sensitive resistor can provide haptic feedback through the use of printed coils and a fixed magnet.
That causes the resistor and Twelve layer printed coils are used to launch a small Neodymium Iron Borate magnet. We use short 10 ms pulses in the coil at 30 Volts. This video shows five printed coils mounted on the tone bridge of a guitar. The audio is actually being played through the speaker coils and magnets are driving the acoustics of the guitar.
Essentially this is a self-playing guitar. We discovered that you could also use the engine as a speaker for music. Using Nitinol or Flexinol to replace Solenoids All of the actuators below can be used to actuate solenoids.Lightest actuators actived by heat or electricity. Nitinol spring is widely used in temperature control valves and other applications require linear actuations.
Given the complex nature of Nitinol and of course its spring form, we have listed following steps as your Nitinol spring selection guide. Feel free to contact u s anytime to talk about your product needs, and our experienced engineers will be happy to recommend or design the spring that will fit your needs.
The benefit of one-way springs is that they are lower cost than two-way springs. However, a one-way spring needs to be deformed by an external force when cooled. So, if your application does not readily provide this biasing force, additional components may need to be added to the system, increasing cost, size and weight.
A two-way spring automatically resets itself when cooled, eliminating the need for a biasing force. This allows actuators to be put into extremely tiny packages. For many applications, the reduction in components offsets the higher cost of the two-way spring. We can customize everything, but if you need a one-way, spring, we have more than one million part numbers in stock and ready to be purchased online: Micro-Spring and Helical Spring.
A tension spring is a spring where the pitch is equal to the diameter of the wire closed wrap. This spring can only exert tension on a system because the closed wrap cannot be compressed in any way. Of course, the exception to this is a two-way spring, because it can exert force in both directions. A spring with a pitch greater than the wire diameter can be either extended or compressed. These springs are referred to as compression springs or extension springs, depending on their application.
Nitinol Actuators by Miga Technologies LLC
Increasing the pitch of the spring increases the stiffness and decreases the travel of the spring. Choosing the proper transition temperature for your application is critical for your project to be a success. For electrically actuated springs, choosing a higher transition temperature yields a faster cycle rate while a lower transition temperature consumes less electricity.
For applications that use a heat source and sink to actuate the spring, the transition temperature should be a little lower than that of the heat source. For superelastic springs, the stiffness of the spring increases as the temperature increases away from the transition temperature. Additionally, the amount of recoverable deformation is maximum close to the transition temperature.
Nitinol is extremely sensitive to chemical composition, so choosing the proper alloy is very important. Here is some basic information on some of the alloys available:. NiTi: The basic nitinol alloy. NiTi exhibits the largest deformation recovery and is used in the vast majority of nitinol springs that we manufacture.
Ultimate tensile strength
NiTiCu: Adding copper to the nitinol reduces hysteresis and improves fatigue properties. The tradeoff is a dramatically reduced recoverable deformation.Nitinol is a shape memory alloy composed of near equal parts of nickel and titanium. Nitinol exhibits two unique properties: superelasticity and shape memory. Superelasticity refers to the ability of Nitinol to accommodate large recoverable strains within a given temperature range. Shape memory refers to the ability of Nitinol to deform at a given temperature and recover to its original shape upon heating above its transformation temperature or austenite finish [Af] temperature.
These unique properties of Nitinol, along with its biocompatibility, make it an attractive option for self-expanding stents used in transcatheter aortic valve implantation TAVI procedures. The performance of a Nitinol self-expanding stent is impacted by the raw material, stent design and stent processing.
Optimisation of all three aspects is needed to achieve clinically relevant stent performance parameters, including acceptable Af temperature, radial forces, flexibility and long-term fatigue performance. The St. The unique properties of Nitinol — superelasticity and shape memory — are derived from its ability to undergo reversible phase transformation.
Upon the application of temperature or stress or a combination of both, Nitinol undergoes phase transformation between austenite and martensite see Figure 1. Download original Open in new tab. Martensitic Nitinol is highly malleable when compared to austenite. Superelasticity When Nitinol phase transformation is driven by external stress or force above its transformation temperature, it is called superelasticity.
The application of an external load transforms Nitinol from austenite to martensite. Upon release of the load, martensite transforms back to its original parent or austenite phase. Superelasticity in Nitinol is characterised by a difference in the loading and the unloading curve during the application of a force or load. For example, when Nitinol stents are loaded into the delivery system, the stent undergoes phase transformation from austenite to martensite along the loading part of the curve see Figure 2.
Upon deployment in the body, stent expansion occurs along the unloading part of the curve as martensite converts back to the austenite phase. This property is utilised in the Portico valve design and manufacturing to enable resheathability on one side while allowing for acceptable anchoring and sealing of the valve on the other.
When Nitinol transformation is driven by change in temperature, it is called shape memory. Decreasing the temperature below a certain limit martensite start temperature [Ms] leads to the formation of martensite, making Nitinol more malleable see Figure 3. On heating beyond the Af temperature, the material transforms to its original austenite phase, thus recovering its shape. The stent design and the manufacturing process are controlled to achieve a balance between key performance parameters.
The Af temperature of the stent is set below body temperature to ensure that the valve fully opens to the annulus diameter on deployment and has sufficient radial force to seal and anchor. In addition, the stent radial force during compression is optimised to allow valve prep and loading at room temperature, and full resheathability at body temperature.
The design exploits the biased stiffness properties of Nitinol to ensure sufficient chronic outward radial forces for sealing and apposition of the valve in its intended use range within the annulus. This is in contrast with first generation TAVI self-expanding stent technologies that require cold temperatures to manipulate the Nitinol for valve loading. The open cell stent design of the Portico valve has two primary sections: the annulus and the aortic.
The intended functions of the two sections are noted below. Annulus Section — higher cell density and provides support for the valve.Tim's Nitinol Flower
It has higher radial force for optimal anchoring, apposition and sealing.Nickel titaniumalso known as Nitinolis a metal alloy of nickel and titaniumwhere the two elements are present in roughly equal atomic percentages. Different alloys are named according to the weight percentage of Nickel, e.
Nitinol 55 and Nitinol It exhibits the shape memory effect and superelasticity at different temperatures. Nitinol alloys exhibit two closely related and unique properties: the shape memory effect and superelasticity also called pseudoelasticity.
Shape memory is the ability of nitinol to undergo deformation at one temperature, stay in its deformed shape when the external force is removed, then recover its original, undeformed shape upon heating above its "transformation temperature".
Superelasticity is the ability for the metal to undergo large deformations and immediately return to its undeformed shape upon removal of the external load. Nitinol can deform times as much as ordinary metals and return to its original shape. Whether nitinol behaves with the shape memory effect or superelasticity depends on whether it is above the transformation temperature of the specific alloy. Below the transformation temperature it exhibits the shape memory effect, and above that temperature it behaves superelastically.
The word Nitinol is derived from its composition and its place of discovery: Ni ckel Ti tanium- N aval O rdnance L aboratory. William J. Buehler  along with Frederick Wang discovered its properties during research at the Naval Ordnance Laboratory in Having found that a alloy of nickel and titanium could do the job, in he presented a sample at a laboratory management meeting. The sample, folded up like an accordionwas passed around and flexed by the participants.
One of them applied heat from his pipe lighter to the sample and, to everyone's surprise, the accordion-shaped strip contracted and took its previous shape. While the potential applications for nitinol were realized immediately, practical efforts to commercialize the alloy did not take place until a decade later. This delay was largely because of the extraordinary difficulty of melting, processing and machining the alloy.
Even these efforts encountered financial challenges that were not readily overcome until the s, when these practical difficulties finally began to be resolved. The same effect was observed in Cu-Zn brass in the early s.
At high temperatures, nitinol assumes an interpenetrating simple cubic structure referred to as austenite also known as the parent phase. At low temperatures, nitinol spontaneously transforms to a more complicated monoclinic crystal structure known as martensite daughter phase. Starting from full austenite, martensite begins to form as the alloy is cooled to the so-called martensite start temperatureor M sand the temperature at which the transformation is complete is called the martensite finish temperatureor M f.
When the alloy is fully martensite and is subjected to heating, austenite starts to form at the austenite start temperatureA sand finishes at the austenite finish temperatureA f. The hysteresis width depends on the precise nitinol composition and processing. Crucial to nitinol properties are two key aspects of this phase transformation. First is that the transformation is "reversible", meaning that heating above the transformation temperature will revert the crystal structure to the simpler austenite phase.
The second key point is that the transformation in both directions is instantaneous.