Presentation on theme: "Lesson 8 2014. Lesson 8 2014 Our goal is, that after this lesson, students are able to recognize the main groups of adaptive materials with their typical."— Presentation transcript:
Our goal is, that after this lesson, students are able to recognize the main groups of adaptive materials with their typical adaptive properties and are able to evaluate the possibilities to utilize adaptive materials in engineering applications.
Adaptive materials have properties, which can be changed ”dramatically” by different stimulus. E.g. viscosity, density, volume, thermal or electrical conductivity can be changed in that way. Properties of ”ordinary” materials do also change e.g. due to temperature changes. E.g. viscosity changes due to temperature, but the change is only limited, while the viscosity of adaptive materials can be changed rapidly from solid to liquid and vice versa. The stimulus to produce the “dramatic "change of selected properties could be temperature, light, humidity, pH-value, changes of electric or magnetic fields etc. What’s the difference between adaptive and ordinary materials?
Briefly about the terminology Several terms are used with different emphasis : Smart materials Intelligent materials Active materials Adaptive materials Functional materials (Adaptive) ”Material” vs. ”Surface” vs. ”Layer”
Design of intelligent products INTELLIGENT PRODUCT OR SMART MACHINE ABILITY TO ”OBSERVE” THE ENVIRONMENT ABILITY TO ”OBSERVE” THE ENVIRONMENT ABILITY TO ”MAKE DECISION” BASED ON STIMULUS (INPUTS) ABILITY TO ”MAKE DECISION” BASED ON STIMULUS (INPUTS) ABILITY TO ”REACT AND/OR ADAPT” TO THE CHANGES OF THE ENVIRONMENT ABILITY TO ”REACT AND/OR ADAPT” TO THE CHANGES OF THE ENVIRONMENT ABILITY TO COMMUNICATE WITH THE USER AND/OR ENVIRONMENT WHAT INTELLIGENT FEATURES ARE REQUIRED? WHAT IS NEEDED TO ENABLE THESE INTELLIGENT FEATURES? SENSOR TECHNOLOGY MONITORING TECCNOLOGY CONTROL- TECHNOLOGY DATA TRANSFER TECHNOLOGY UTILIZATION OF ADAPTIVE MATERIALS
INPUT MEMORY MATERIALS MAGNETOSTRICTIVE MATERIALS PIEZOELECTRIC MATERIALS Change of the electric field Change of the magnetic field Change of the temperature TiNi, TiPd TbFe, (TbDy)Fe, SmFe PZT, Quartz MAIN GROUP OF ADAPTIVE MATERIALS EXAMPLES OF MATERIALS
Piezoelectric materials are used in sensors to measure impact forces or density (viscosity) values of liquids. Piezoelectric materials are also used in quartz clocks, electrical drums and guitars, microphones etc. Piezoelectric sensors are manufactured by powder metallurgy Examples of piezoelectric materials: Aluminium phosphate (AlPO 4 ) Some fluoropolymers Gallium phosphate (GaPO 4 ), Some ceramics (BaTiO 3, KNbO 3, LiNbO 3, LiTaO 3, BiFeO 3, Na x WO 3, Ba 2 NaNb 5 O 5, Pb 2 KNb 5 O 15 ).
Function Additional measurement of absolute pressure through deformation of the door in a side crash and additional sensing of absolute pressure Installation within the side door Sensing principle Piezo-resistive, micro-mechanical pressure sensor with highly- integrated evaluation electronics
How to measure and evaluate adaptive properties? Output strain [m/V] Output strain/affecting electric field strength -ratio Output electric field strength [Vm/N] Output electric field strength /affecting mechanical stress -ratio Characteristic describing the change between energy types = Stimulating mechanical energy/produced electric energy -ratio (or vice versa) These characteristics might have different values in different directions of the sensor
Electro- ands magnetostrictive materials Electrostrictive materials strain due to the applied electric field. They are (unlike the piezoelectric materials) not poled. The most prominent electrostrictive material is lead magnesium niobate (PMN). Magnetostrictiive materials change their length when subjected to a magnetic field. Magnetostrictiive materials generate a magnetic field when they are deformed by an external force. Magnetostrictive materials can be used for both sensors and actuators. Commercially-available magnetostrictive materials are based on Terbium (Te), Iron (Fe), Dysprosium (Dy) alloys.
Magnetostrictive effects Joule effect : When subjected to an magnetic field the length of the material will change. (Used in magnetostrictive actuators.) Villari effect: When a mechanical stress is imposed on a sample, there will be a change in the magnetic flux density. (Used in magnetostrictive sensors.) Barret effect: The volume of the material change in response to the magnetic field.
ELECTROSTRICTIVE FIBRES ARE USED TO DAMP VIBRATIONS OF SNOWBOARDS
When skiing at high speeds and on tough terrain, skis tend to vibrate, decreasing the contact area between the snowboard edge and the snow surface. This results in reduced stability and control and decreases the skier's speed. Smart snowboards overcome these limitations by utilizing the integration of electrostrictive sensors and an actuator control system. The electrostrictive ceramics or fibers embedded in the snowboard convert the unwanted vibrations into electric energy, thus keeping the snowboard on the snow.
Electrorheological materials Electrorheological (ER) materials’ flow, viscosity damping capacity internal friction the ability to absorb energy under impact depend on the strength of the affecting electric field. At high enough electric fields, the liquid materials can solidify rapidly (in milliseconds) into viscoelastic solids. This phenomenon is instantly reversible, if the electrical field is removed.
ER materials are typically fluids, gels or elastomers. ER materials may consist of different types of mixtures such as silicon oxide gel, talcum powder and various polymers with liquids such as kerosene, mineral oil, toluene and silicone oil work. Some applications: Improvement of the vibration control characteristics of an damping absorber using ER fluid as the working fluid inside the absorber. ER fluid based application of a clutch for direct coupling device in power transmission system of rotating machinery.
Magnetorheological materials The function of magnetorheological materials (MR)is analogic with electrorheological materials. At high enough magnetic fields, the liquid materials can solidify rapidly (in milliseconds) into viscoelastic solids. This phenomenon is instantly reversible, if the magnetic field is removed.
Shape memory materials (SMM) Shape memory materials (SMMs) are featured by the ability to recover their original shape from a significant plastic deformation when a particular stimulus is applied. This is known as the shape memory effect (SME). Typically the stimulus is heat. Superelasticity (in alloys) or visco-elasticity (in polymers) are also commonly observed under certain conditions. Most of the memory properties are based on the changes of the crystal structures of the materials. An other remarkable stimulus of shape memory materials (MSM-materials) is magnetic field.
Metallic Shape memory alloys (SMA) AuCd and AgCd alloys were the first memory alloys Three alloy systems NiTi-based Cu-based (CuAlNi, CuSn, CuZnAl) Fe-based have the largest commercial importance. All these SMAs are thermo-responsive, i.e., the stimulus required to trigger the shape recovery is heat (not more than 10 degrees change of the temperature might start the adaptive function).
NiTi-based alloys should be the first choice if high performance and good biocompatibility are required. However, the manufacturing processes of NiTi-alloys is challenging. Cu-based SMAs have the advantages of low material cost and good workability in processing. Fe-based SMAs are used as a fastener/clamp for one-time actuation due to the extremely low cost. Shape memory materials, which react to the changes of the magnetic field are usually based on Ni-Mn-Ga-alloys (eg. Ni 2 MnGa). The deformation due to stimulus could be even 10%.
PZT- material MSM Ni-Mn-Ga Control FieldElectricMagnetic Max. strain ξ (µm/mm), linear0.3100 Compressive strength (MPa)60700 Max. operating temp. (°C)10070 Field strength for max. strain2 MV/m 400 kA/m COMPARISON OF MSM MATERIALS
Shape memory polymers (SMP) Advantages of SMPs compared to metal alloys: Tailoring the material properties of polymers is much easier. Both the material cost and the processing cost of polymers are much lower. SMPs are much lighter. Different stimuli can be utilized: The stimulus could be heat, UV- or infrared light, moisture or pH change. Many SMPs are naturally biocompatible and even biodegradable. Some typical materials: The thermoplastic polyurethane (e.g. in clothes) Composites with fillers based on SiC nanoparticles) Ni powder in a polyurethane SMP/carbon black composite.
Other shape memory materials Shape memory composites Shape memory composites (SMC), which include at least one type of SMM, either SMA or SMP, as one of the components Shape memory hybrids Shape memory hybrids (SMH) are made of conventional materials. They are based on the dual-domain system, in which one is the elastic domain and the other is the transition domain, which is able to change its stiffness remarkably if the stimulus is present.
Auxetic materials Auxetic materials are a special kind of materials that exhibit negative Poisson’s ratio effect. They get fatter when stretched and thinner when compressed. Auxetic behavior is can be achieved at different structural levels from molecular to macroscopic levels. The internal (geometrical) structure of material plays an important role in obtaining auxetic effect The behaviour of the auxetic material could be illustrated as a desired “function of a mechanism”.
Auxetic materials Practical examples: Auxetic polyurethane (PU) foam Auxetic microporous PTFE Some forms of graphite Ni 3 Al crystals Carbon/epoxy, Kevlar/epoxy or Glass/epoxy composites could have auxetic properties in a minor scale. Advantages: Adjustable strength and rigidity based on the loading direction Improved ware resistance Improved ductility of fibre reinforced composites
F pull THE STRUCTURE GETS THINNER THE STRUCTURE GETS THICKER Principal function of auxetic materials ORDINARY AUXETIC
F pull MATRIXFIBRE TRADITIONAL FIBRE GETS THINNER UNDER TENSILE LOAD AUXETIC FIBRE GETS THICKER UNDER TENSILE LOAD IMPROVING THE DUCTILITY OF FIBRE REINFORCED COMPOSITES
Properties of the foam can be specified by defining three independent characteristics: 1. Pore Size 2. Relative Density 3. Base Material
Chromogenic materials Chromogenic materials are able to change their optical properties in response to an external stimulus such as temperature, light, electrical current or pressure etc.
Photochromic Thermochromic Electrochromic Solvatochromic Lonchromic Tribochromic Piezochromic Light Temperature Current Polarity of liquids Ions Mechanical friction Mechanical pressure CHANGE OF THE OPTICAL MATERIAL PROPERTIES MATERIAL GROUPS CHROMOGENIC MATERIALS STIMULUSOUTPUT
Biologically active materials The most important material property is biocompatibility (non-rejection property) Applications: Bio-electric prosthetic nose Taste receptors of an electronic artificial tongue: Vibrotactile sensing elements for artificial skin applications Artificial skin made of polymer applications like synthetically manufactured collagens and polypeptides Making individually tuned “spare parts” for a human body (like bones of ceramics) “So-called Tissue engineering”
Phase change materials (PCM) In theory when the temperature rises, the PCM melts and the material absorbs heat. When the temperature drops, the PCM solidifies, and heat is emitted. During the phase change, the temperature remains constant. Of course ordinary materials do also absorb and emit heat energy, but their phase remains the same. PCM’s capacity to absorb and emit heat energy could be 5…10 times higher compared with ordinary materials. Possible PCM material types: Polyethylene-paraffin compounds, mixtures based on hydrated salts such as CaCl 2 +6H 2 O, Na 2 SO 4 +10H 2 O, Na 2 HPO 4 +12H 2 O, NaCO 3 +10H 2 O, and Na 2 S 2 O 4 +5H 2 O.
pH-active materials Microcapsules embedded in a coating can detect corrosion by detecting the pH-change caused by it and release their contents automatically to indicate, protect, and repair damaged areas.
Adaptive gels Different ways to classify adaptive gels: Applications of adaptive polymer gels in general Polymers with electric conductivity properties Insulating elastomers Ferrogels
The initial volume of polymer gels can be increased 1000-times larger based on stimulating pH, temperature or electromagnetic field changes The size of the artificial muscle is near the size of real human muscle (if the performance is about the same) Smart gels can have either electro- or magnetostrictive properties Some important polymer gels: - PVA - PAA - PAN
Electrostrictive gels: Applications of PMMA Ferrogels made of PVA-polymer and Fe 3 O 4 mixture Electrically conductive polymers: PAni PPY PPV