Propiedades Mecánicas de los Polímeros
Resistencia
La resistencia es una propiedad mecánica que usted podría relacionar
acertadamente, pero no sabría con exactitud qué es lo que queremos
significar con la palabra "resistencia" cuando hablamos de polímeros.
En primer lugar, existen varios tipos de resistencia. Está la
resistencia tensil. Un polímero tiene resistencia tensil si soporta un
estiramiento similar a éste:
La resistencia tensil es importante para un material que va a ser
extendido o va a estar bajo tensión. Las fibras necesitan tener buena
resistencia tensil.
Luego está la resistencia a la compresión. Un polímero tendrá
resistencia a la compresión si soporta una compresión como ésta:
El concreto es un ejemplo de material con buena resistencia a la
compresión. Cualquier cosa que deba soportar un peso encima, debe
poseer buena resistencia a la compresión.
También está la resistencia a la flexión. Un polímero tiene
resistencia a la flexión si soporta una flexión como ésta:
Existen otras clases de resistencia de las que podríamos hablar. Un
polímero tiene resistencia a la torsión si es resistente cuando es
puesto bajo torsión. También está la resistencia al impacto. Una
muestra tiene resistencia al impacto si es fuerte cuando se la golpea
agudamente de repente, como con un martillo.
¿Qué es la resistencia?
¿Pero qué significa ser resistente? Tenemos una definición bien
precisa. Emplearemos la resistencia tensil para ilustrarlo. Para medir
la resistencia tensil de una muestra polimérica, tomamos la muestra y
tratamos de estirarla tal como se muestra en la figura de arriba.
Generalmente la estiramos con una máquina llamada Instron. Esta
máquina simplemente sujeta cada extremo de la muestra y luego procede
a estirarla. Mientras dura el estiramiento de la muestra, va midiendo
la fuerza (F) que está ejerciendo. Cuando conocemos la fuerza que se
está ejerciendo sobre la muestra, dividimos ese número por el área (A)
de la muestra. El resultado es la tensión que está experimentando la
muestra.
[IMAGE]
Luego, usando nuestra máquina, seguimos incrementando la fuerza, y
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