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# CustomStrainDegradation

Strain History Based Degradation With Custom Rules

This model implements the [universal damage model](/suanpan-manual/material/material1d/degradation/degradation.md) assuming the degradation factor depends on the strain history.

## Syntax

```
material CustomStrainDegradation (1) (2) (3) [4]
# (1) int, unique material tag
# (2) int, host intact material tag
# (3) int, tension degradation expression tag
# [4] int, compression degradation expression tag, default: (3)
```

## Usage

The usage of `CustomStrainDegradation` is identical to [`CustomStressDegradation`](/suanpan-manual/material/material1d/degradation/customstressdegradation.md).

The degradations for positive/negative strains are defined separately.

$$
D\_{pos}=D\_{pos}(\varepsilon\_{max}),\quad
D\_{neg}=D\_{neg}(\varepsilon\_{min}).
$$

In which $$\varepsilon\_{max}$$ is the maximum strain (positive) of the whole loading history, and $$\varepsilon\_{min}$$ is the minimum strain (negative) of the whole loading history.


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