A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The overall goal of this procedure is to improve the design and safety of polymer and polymer composites under complex loading conditions. Through the study of their durability under concurrent hydrothermal and mechanical loads, using a low cost flexible user-friendly testing platform. First, polymer composite specimens are positioned into a testing tank.

Next, a constant three point bending load is applied, and the specimen is concurrently immersed in fluid with creep loading. The measured resistance readings are converted into displacement changes. For analysis, the weights of the specimens are measured after the concurrent tests.

Lastly, the specimens are tested for their residual strength. Thus, the mechanical and design purposes of materials are better understood based on their response to the concurrent loading. The main advantage of this platform over existing methods is that it is low cost, user-friendly, portable, and easily adaptable to other testing needs.

The applications of this work stands towards safer engineering structures made of polymers and polymer composites, such as aircraft, ships, bridges, and wind turbines. We will have better understanding and therefore better numerical models and designs of these structures under complex service conditions. We're currently using this method in order to provide insight into the durability of polymers and polymer composites, immersed in water and under mechanical load.

However, it can also be applied to other situations such as the durability of other materials that are routinely subjected to harsh chemicals during service. Generally, individuals new to this platform should pay attention to carefully positioning and loading the samples. The chamber of the testing apparatus is constructed of high density polyethylene, which will robustly tolerate a wide range of temperatures and fluids.

Polystyrene foam surrounding the testing tank prevents heat exchange with the environment. The lid of the chamber is 9.5 millimeter thick polycarbonate, which allows for viewing of the loaded specimens. It is secured by aluminum T-bar, which are in turn secured to the tank to accommodate a heavy load.

A reinforcing steel frame and additional hooks on the lid are applied. Heavier weights are most often used for residual strength tests. This chamber can apply up to 50 kilograms to each specimen to ensure that the fail point is found.

Hanging down from the lid are three aluminum blocks designed to A STM standards. These blocks allow up to four specimens to be tested simultaneously and are adjustable through slots in the chamber lid. The specimens are positioned beneath two of the blocks and an upward force at the center of a block induces bending forces on the specimen.

The apparatus has mobile casters at its base and is solidly held together by a steel frame with cross beams and meshing for support. Angled spacers keep the insulation from being crushed by the overhead weight and displacement gauges on the frame pulley and string potentiometer systems measure the mid-span deflections. These potentiometers are constructed of torsional springs.

The pulley connect steel cable from a connection by the specimen to a hanging rod for adjustable weight application. The total load applied to the specimen comes from this series of cables, pulley linkages, and bolts. These are explained in the following sections, covering the use of the apparatus to load a specimen into the testing apparatus.

First, open the lid of the tank and set the lid onto the side supports. Then load the specimen into the U-bolt. The crossbar must be at the center of the specimen.

Now rest the ends of the specimen on the aluminum support. There should be about five to 10 millimeters of overhang. Continue loading up to four specimens in the same manner.

Then remove the lid supports and lower the lid. Make certain that the lid is correctly seated on the tank. Now, apply the desired force to the specimens by adding weights to the steel rod hanging from the outer pulley.

First, make sure the potentiometer line is tight. Then measure the resistance across the outer pins of the potentiometer. The black lead goes to pin one and the red lead goes to pin three.

Now, convert the resistance reading into displacement by computing the calibration factor. In this case, one kilo ohm corresponds to 64.895 millimeters of displacement. For continuous data acquisition, it is possible to connect the string potentiometers to the digital multimeter.

After calculating displacement, prepare to weigh the specimens, remove the weights, and the lid of the tank. The specimens can then be transferred to the holding chamber. First, prepare an interim holding chamber for all the specimens with room temperature, testing fluid of the appropriate testing standard.

Now to weigh a specimen first, dry it off with a microfiber cloth. Then place it on a high precision scale and record the data reading. If the specimens need to be tested for residual strength, proceed with those tests.

High growth thermal mechanical tests were conducted at room temperature on two groups of four specimens of closed cell polyurethane foam. One group was tested dry at 50%relative humidity. The second group was tested wet in deionized water.

Mid-span deflection was tracked for the first six hours and later the next day. The wet specimens displacement was substantially greater than the dry specimens. The residual strength of the specimens was tested by loading until failure.

The wet specimens failed at about three kilograms, and the dry specimens failed at about 3.6 kilograms. If the setup is performed properly, the specimens can be positioned and loaded in this platform in 15 minutes. While following this procedure, it's important to remember to position and load the samples properly, especially if they require a significant weight for the durability study Following this procedure.

Other studies such as the durability of composites and harsh service chemicals can be performed in order to answer additional questions on the durability of these materials. After watching this video, you should have a good understanding of how to test polymers and polymer composites using these low cost user-friendly testing setup. If working with harsh chemicals, remember to adhere to the precautions indicated in the material safety sheets and environmental health and safety.