I’ve had a few car breakdowns in my life that have left me stranded on the highway. Whenever this happens, I envy the lucky people who manage to live life without the need to own or drive an automobile on a daily basis. The trouble is that there is no way I can do all that I want to do in the time I have available without having my own car. Besides, my hatred of my vehicle quickly passes when I think about how reliable my car actually is. When you think about that there are roughly 30,000 individual parts in a modern automobile and with all the abuses we subject all these parts to — potholes, temperature extremes, lack of maintenance — it’s truly amazing that problems arise as seldom as they do. That’s because an incredible amount of R&D effort and testing goes into making sure all of these parts are properly engineered into the system.
For example, take a look at the automotive interior. Here you have a seemingly infinite number of adhesives, plastics and textiles assembled into a complicated web of parts that create a luxurious and safe driving environment. Complicating the matter, all of this is done knowing full well that this needs to be done as inexpensively as possible because, ultimately, this precision engineered driving machine will be disposed of in a little over a decade.
We here at ADMET have a long history in the automotive industry and have seen a lot of automotive interior testing over the years. Our universal testing systems — commonly referred to as tensile / compression testing machines or UTM’s — are used to test a wide array of interior parts. Here are a few interesting examples:
Seating textiles in a tensile test — The strength of a seating textile can be obtained by taking cut strips of the fabric and pulling them apart in a tensile strength test. This test measures how much force is required to break the strips (tensile strength) and how far they stretched before doing so (elongation or % stretch at break).
Door trim panel laminate peel tests — We’ve all seen door panels where the textile or leather is puckering away from the door trim. There are many causes of this but often it is the result of the glue failing to hold the surface fabric to the underlying substrate. A UTM can perform a peel test that measures the force required to separate two pieces of material that have been glued or otherwise bonded together. To simulate the durability of the assembly, the peel test is done before and after aging in a heating, cooling, and humidity chamber.
Rubber bumper compression deflection testing — Look closely and you will find small rubber pieces all over the inside of a vehicle. They provide a nice dampened sound when closing center console lids, glove compartments, cup holders, etc. The bumpers also keep the things that close on them from rattling. They need to be carefully chosen because if they provide too much resistance, the parts that close on them won’t be able to close or there will be an ergonomic aggravation. These bumpers are designed into the system with knowledge of their compression deflection characteristics which are obtained in a compression test performed on a universal testing machine.
Rubber nub commonly found in automotive interiors
Seating foam support testing – A seating cushion needs to feel soft but also be supportive. Cushions are tested in what is called an Indentation Force Deflection test where the cushion is compressed to 25% and 65% of its thickness. Force readings are taken at both compression points. Values that are too high or low mean that the seat is either too hard or soft, respectfully. Seating engineers identify the ideal amount of support each cushion should have and assign a target IFD value. The value is based on the purpose of the vehicle. For example, a minivan may be designed to have firm front seats (high IFD values) which are best for adults on long road trips and soft seats (low IFD values) in back for kids.