Polymer stress strain curve pdf

Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. Dumitru Olaru. Stelian Vlad. Gheorghe Prisacaru. A short summary of this paper. Download Download PDF. Translate PDF. Recently, the electroactive polymers are emerging as possible candidates for actuators and sensors applications at micro and nano scales. Generally, the characteristics like large strain, high stress, high energy density, good efficiency and high response speed are required to obtain a good overall actuator performance.

The mechanical tensile tests were performed on elastomer specimens using a tensile test machine from TIRA, Germany. The preliminary results showed an elastic modulus ranging from 0. We concluded that the tested elastomers are suitable for the electroactive polymer actuators, for example, as microactuation systems in MEMS technology.

Keywords: Electroactive polymers, silicone elastomer, actuators, tensile test 1. It dates back to the early work by Kuhn and Katchalsky [1], in the fiftieth, but the progress has especially been obtained from till today. The electroactive polymers EAPs materials are an alternative to the materials commonly used for actuators and sensors, e.

EAPs are materials that produce the significant shape and size change in response to the electrical stimulation current or voltage. In order to transform these materials from the developing phase to an application as effective actuators, there is a need for an established infrastructure.

Having the actuation capability in addition to the other advantages of the polymers, including lightweight, low cost and fracture tolerance, all make these materials highly attractive. These materials can be used to make the mechanical devices and the robots with no traditional components like gears and bearings, which are responsible to their high costs, weight and premature failures [2]. Th electroactive polymers can be divided into two major categories based on their activation mechanism, including ionic and electronic.

The electronic EAP are driven by Coulomb forces and they include: dielectric EAP, electrostrictive graft elastomers, electrostrictive paper, electro-viscoelastic elastomers, ferroelectric polymers and liquid crystal elastomers LCE. This type of EAP materials can be made to hold the induced displacement while activated under a high DC voltage, have a great mechanical energy density and they can be operated in air with no major constraints, allowing them to be considered for the robotic applications.

In contrast to the electronic EAP, the ionic EAP are materials that involve the mobility or the diffusion of the ions and they consist of two electrodes and an electrolyte. The activation of the ionic EAP can be made by as low as 1—2 V and mostly a bending displacement is induced. The induced displacement of both the electronic and ionic EAP materials can be designed geometrically to bend, stretch or contract [2].

Recently, much attention has been paid to the soft elastomers, mostly silicone [] and acrylic elastomers [], as dielectric electroactive polymers DEAPs , in the field of novel actuator technology. VHBTM acrylic elastomers from 3M have been widely used in the actuators and have shown good performance by producing large strains [,11,12].

However, in contrast to the acrylic elastomers, the silicones have the possible advantages of a high stability over a wide temperature range, a fast response speed and a high efficiency [13, 14]. For this reason, there is a growing interest in developing new silicone elastomers as dielectric materials. Recently, Michel et al. They determined the passive material properties in four different tests uniaxial tensile test at various temperatures, uniaxial stress relaxation test at ambient temperature, uniaxial cyclic strain test at ambient temperature and torsional dynamic mechanical thermal analysis - DMTA and the active behavior in the electromechanical tests.

They concluded that the elasticity of silicone DC is approximately 0. It has low viscosity and fast electromechanical response time 3 s. In contrast, the acrylic elastomer shows a strong temperature dependence of the elastic modulus and the actuators made from this material should be operated in a controlled ambient environment. It has a long electromechanical response time and high viscosity.

All tests were made at room temperature. Due to the interesting properties, PDMS play a structural role in MEMS, serving as protective layers, encapsulates, valve diaphragms, micropumps, fluidic channel structures, etc. Also, it has been used for developing modulable optical systems and as a biomaterial in catheters, drainage tubing, insulation for pacemakers, membrane oxygenators, ear and nose implants [16], bio-compatible substrate for cell behavior studies [17,18].

The stress-strain curve of the most widely used ductile material Steel is shown in Fig. For Aluminum the yield strength is not distinct; So the yield strength is decided using the proof stress method.

Cast Iron is a brittle material. For brittle materials, yield strength is not present as these materials fail all of a sudden. So, tensile strength is the main important parameter for brittle materials like Cast Iron, glass, and Concrete. Elastomers normally exhibit permanent plasticity. So, the stress-strain curve of elastomers is quite different from ductile and brittle materials. Perfectly plastic or ideal plastic material will not show any work-hardening during plastic deformation.

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It is caused by orientation and allignment of polymer chains in the direction of the load which increases the strength and stiffness of the plastic in stretch direction and explains the observed increase in true stress.

The opposite of strain hardening is strain softening. Amorphous polymers, when physically aged, exhibit soemtimes true strain softening. Miehe et al. When the temperature exceeds the glass transition temperature, the plastic material abruptly changes its mechanical behavior. In this region, the ultimate extension can be very high at rather low loads. In some cases, it can exceed several hundred percent before failure occurs. The behavior before break will depend on the crosslink and entanglement density; materials that are lightly crosslinked will undergo large elastic deformation prior break, whereas uncrosslinked polymers will show viscoelastic behavior.

The brittle-ductile transition temperature, T b , is not always identical with the glass transition temperature, T g. Strain hardening is sometimes erroneously called "strain softening" when the shear or tensile resistance decreases with increasing strain. The observed drop in stress beyond the yield point is caused by a reduction of the cross section area necking.

The true stress, however, which is the load divided by the actual cross-sectional area, typically increases. Miehe, S. Goektepe and J. Mendez Diez, Int. Of Solids and Structures , Vol. The mechanical behavior of a plastics depend on the composition, strain rate, molecular weight, crosslink density, and temperature. Brittle materials break at the stress maximum and at low strain, whereas ductile materials undergo yielding followed by a drop in stress and break at noticeable lower stress but much higher strain.

At low stress, the deformation of most solid plastics is elastic.