This is what I've found.

deformació per fluència lenta ---> creep

https://glosbe.com/ca/en/fluència

In materials science, creep (sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods and generally increases as they near their melting point.

https://en.wikipedia.org/wiki/Creep_(deformation)

Creep
• It is a time- dependent deformation under a certain applied load.
• Generally occurs at high temperature (thermal creep), but can also happen at room temperature in certain materials (e.g. lead or glass), albeit much slower.
• As a result, the material undergoes a time dependent increase in length, which could be dangerous while in service.

https://web.iit.edu/sites/web/files/departments/academic-aff...


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Note added at 4 hrs (2020-09-04 13:46:30 GMT)
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Thermal creep is a term that describes an occurrence where materials permanently shift or deform in shape as a result of applied stress and...

https://www.google.co.uk/search?ei=lkFSX7riF4i4a6DpvPgH&q=th...

What is creep? Creep may be defined as a time-dependent deformation at elevated temperature and constant stress. It follows, then, that a failure from such a condition is referred to as a creep failure or, occasionally, a stress rupture. The temperature at which creep begins depends on the alloy composition. For the common materials used in superheater and reheater construction, Table I (see below) gives the approximate temperatures for the onset of creep. It should be pointed out that the actual operating stress will, in part, dictate or determine the temperature at which creep begins.

https://www.nationalboard.org/Index.aspx?pageID=181

Viscoelastic solids have molecules in which the load-deformation relationship is time-dependent. If a load is suddenly applied to such a material and then kept constant, the resulting deformation is not achieved immediately. Rather, the solid gradually deforms and attains its steady-state deformation only after a significant period of time. This behaviour is called creep. Conversely, the sudden application of a fixed deformation to such a material produces initial stresses that can be very large; these stresses then slowly relax to a steady-state value as the material accommodates itself to the applied deformation. Such a procedure is known as a stress-relaxation test.

https://www.britannica.com/science/deformation-mechanics#ref...

I'm not sure whether you need to include 'thermal'.

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Note added at 6 hrs (2020-09-04 15:58:38 GMT)
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I've just found this:

Uno de los fenómenos dañinos más importantes en el mundo de las plantas industriales es el denominado Fluencia, Termofluencia o más comúnmente Creep, el cual consiste en la deformación dependiente del tiempo de un material, a tensión constante y temperatura elevada. Esta definición nos lleva a poder establecer una advertencia importante para cualquier persona involucrada en el desarrollo de instalaciones y sus componentes: cuando coexistan temperaturas elevadas y tensiones altas y todo ello ocurra en un marco temporal lo suficientemente prolongado, deberemos tener en cuenta el posible impacto del creep en el material que se vea sometido a ello.

https://arvengtraining.com/termofluencia-fluencia-creep/

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Note added at 6 hrs (2020-09-04 16:02:23 GMT)
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And

Cuando evaluamos la resistencia de los materiales a la deformación y fractura sometidos a carga durante largos periodos de tiempo y a alta temperatura, debemos prestar una atención especial al fenómeno conocido como termofluencia (“creep”, en inglés).

http://bibing.us.es/proyectos/abreproy/4358/fichero/Volumen1...