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MATERIALS 41
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Current design standards, such as Eurocode 5, lack freepik.com
comprehensive fatigue-based design rules due to the absence
of reliable analytical models. The next generation of standards
aims to address this gap.

Despite progress, wood fatigue remains a specialised
field. Since fatigue accounts for up to 90 percent of material
failures, a better understanding is crucial for optimising the
use of wood as a renewable resource.
This review synthesises existing literature on the cyclic fatigue
of wood, covering influencing factors, materials, measurement
methods, predictive models, and practical applications. it chars on the surface while retaining a load-bearing core.
Research shows that elevated temperatures accelerate damage
Influence Of Physical Properties formation under cyclic loading, reducing fatigue life.

Firstly, density is a key physical indicator correlated with many Thermal cycling causes expansion and contraction,
mechanical properties. It is closely linked to moisture content potentially leading to microcracks.
and varies with growth conditions and within a single tree For wood's orthotropic nature, it means its fatigue response
(e.g., due to knots, earlywood/latewood). is highly dependent on the load direction relative to the grain.
Research generally indicates that higher density improves In wood materials, different loading conditions result in
fatigue resistance, as it is associated with better mechanical distinct mechanical behaviours. Longitudinal tension exhibits
properties under constant load tests. While some studies show the highest fatigue strength, where failure is characterised by

conflicting results, the consensus is that higher density wood longitudinal crack growth and fibre pull - out.
exhibits superior fatigue performance. Perpendicular tension, on the other hand, shows the lowest
Besides, moisture content significantly influences mechanical static and fatigue strength because the cellular structure is
properties. Up to the Fibre Saturation Point (FSP, typically weak in this direction. Longitudinal compression has a lower
25-30%), an increase in moisture reduces the modulus of fatigue life than tension; damage begins with crushed cell
elasticity, strength, and fatigue life. For instance, LVL samples walls (kinks), eventually leading to a characteristic 45-degree
at 35 percent moisture content showed significantly shorter shear failure.
fatigue life compared to those at five percent. Flexural load is the most common test for wood, with
Moisture interacts with temperature, and rapid moisture failure involving tensile cracks on one side and crushing on

changes can induce internal stresses, leading to damage the other. When stress is normalised to static strength, fatigue
accumulation. High-frequency fatigue testing can cause life is largely independent of species.
localised temperature increases, potentially leading to drying Shear load has a shear strength lower than tensile or
and further altering the material's response. compressive strength, yet its normalised fatigue strength is
In addition, temperature directly affects mechanical comparable to other loading directions.
properties; the modulus of elasticity and strength decrease In torsion, fatigue behaviour differs between hardwoods
as temperature rises. Indirectly, temperature influences relative and softwoods, with hardwoods showing progressive damage

humidity, which in turn affects moisture content. while softwoods fail suddenly.
Wood performs better than steel in fire scenarios because The size of a structural element influences its load-bearing