Fragility (Faults)

Introduction

Britleness is the ability of a material to fracture due to its little or no capacity for permanent deformation. On the contrary, ductile or tough materials break after undergoing some deformations, generally of the plastic type "Plasticity (solid mechanics)"). Brittleness is the opposite of toughness and has the peculiarity of absorbing relatively little energy, unlike ductile rupture.

The energy absorbed per unit volume is given by:.

If a material breaks practically without deformation, the components of the strain tensor are small and the previous sum results in a relatively small amount.

The fragility of a material is also related to the speed of propagation or growth of cracks through its core. This means a high risk of sudden fracture of materials with these characteristics once subjected to stress.[1] On the contrary, tough materials are those that are capable of stopping the advance of cracks.

Typical examples of fragile materials are common glass/hard glass (such as those in windows, for example), some crystalline minerals, ceramic materials and some polymers such as polymethylmethacrylate (PMMA), polystyrene (PS), or polylactic acid (PLA), among others.

It is important to mention that the type of failure offered by a material (brittle or ductile) depends on the temperature. Thus, while some materials such as plastics (polyethylene, polypropylene or other thermoplastics) that usually give rise to ductile fractures at room temperature, below their glass transition temperature they give rise to brittle fractures, such as the steel in wooden houses.

Brittleness, ductility, hardness and toughness

There are other terms frequently confused with fragility that must be clarified:

Improved toughness

Improving toughness is one of the main areas of research in materials science. This point has been especially studied in industrial steels which in some cases, depending on the composition and processing, can give rise to dangerously brittle materials. Achieving improved toughness of materials such as glass would mean losing susceptibility to fracture in accidental or unfortunate cases such as impacts from stones or bullets. The most common way to avoid brittle fracture of glass is by laminating a polyvinylbutyral film (which is a viscoelastic thermoplastic with a refractive index similar to glass) between two sheets of glass so that it absorbs the energy derived from the propagation of cracks.

Fragility (Faults)

Introduction

The energy absorbed per unit volume is given by:.

If a material breaks practically without deformation, the components of the strain tensor are small and the previous sum results in a relatively small amount.

Brittleness, ductility, hardness and toughness

There are other terms frequently confused with fragility that must be clarified:

Improved toughness

Dynamic fragility in solid state physics

Contenido

En física del estado sólido, y en especial en la física de materiales vítreos/amorfos la fragilidad dinámica, m, se refiere a la capacidad de un material de relajarse o relentizarse cuando este se enfría hacia su temperatura de transición vítrea, T.[2][3][4] Normalmente los materiales frágiles presentan una variación muy pronunciada de sus propiedades características en torno a la T, mientras que los materiales más resistentes tienen una variación más moderada a lo largo de rangos de temperatura mayores.[5].

En principio, aún no existe un formalismo que relacione directamente la fragilidad mecánica de un material, tema comentado en los epígrafes anteriores, con la fragilidad dinámica estudiada desde el punto de vista termodinámico-físico. Sin embargo, existen estudios recientes que demuestran que materiales con valores altos del parámetro m, poseen valores bajos de tenacidad mecánica, o capacidad de absorción de energía antes de su rotura.[6][7].

En inglés no existe desambiguación entre el término fragilidad (Brittleness")) empleado para referirse a las propiedades mecánicas y la fragilidad dinámica, m (Fragility")), relacionada con el estudio físico de las propiedades de los materiales a temperaturas cercanas de su T.

Definition

In the more traditional definition of brittleness, originally proposed by Angell, the degree to which the temperature dependence of viscosity, η, deviates from Arrhenius-type behavior is defined as follows:

In this way, the fragility parameter, m, is determined by the value of the slope of the logarithmic representation of the viscosity values (or molecular relaxation times obtained through dielectric spectroscopy, for example) against the inverse of the temperature when it approaches the glass transition temperature, T:.

According to Angell's classification, "resistant" liquids have viscosities (or dielectric relaxation times, for example) with Arrhenius-type behavior with respect to temperature. Silicon (SiO) is a classic example of a "resistant liquid" while o-Terphenyl is the typical example of a "brittle liquid", forming brittle glasses.[5].

Dynamic fragility in solid state physics

Navegación

Fragility (Faults)

Introduction

Brittleness, ductility, hardness and toughness

Improved toughness

Fragility (Faults)

Introduction

Brittleness, ductility, hardness and toughness

Improved toughness

Dynamic fragility in solid state physics

Contenido

Definition

References

Dynamic fragility in solid state physics

Contenido

Definition

References