Why is a matrix division not defined
The keyword in the HIN file is used to control the deletion criteria. The criteria are presented as follows:
where the parameters and must be entered. The keyword must be in the HIN file under the keyword.
For unidirectional composites, the following combinations of TYPE and CRIT are available:* ELEMENT DELETION, TYPE = MATRIX, CRIT = RELOAD Max_Ratio * ELEMENT DELETION, TYPE = MATRIX, CRIT = SPLIT theta * ELEMENT DELETION, TYPE = FIBER, CRIT = ANY
There are two available criteria for TYPE = MATRIX: RELOAD and SPLIT.
TYPE = MATRIX, CRIT = RELOAD
The RELOAD criterion deletes the element when the stress level in the element reaches a certain level after the matrix has failed. After the matrix fails, σ becomesvmt, the proportion of the Von Mises stress from the terms σ22, σ33, σ12, σ13 and σ23, with σvm, the full Von Mises stress (including σ11), compared. Exceeds the ratio of σvmt to σvm a user-defined value, the item is marked for deletion.
The RELOAD criterion evaluates the level of the stress tensor in the directions that are not dominated by fibers. After the matrix failure, we want to keep the stiffness in these directions as low as possible (because the matrix is cracked). However, due to the large strains, the stresses can reload in some cases. With the RELOAD criterion, elements with this behavior can be removed so that they cannot make any significant energetic contributions to the analysis if this is not appropriate.
If is used, the maximum allowable ratio of σvmt to σvm can be specified. This is specified in the first data line after the keyword. Example:* ELEMENT DELETION, TYPE = MATRIX, CRIT = RELOAD 0.2
In this example the element is deleted when σvmt 20% of the total Von Mises stress σvm is or exceeds.
TYPE = MATRIX, CRIT = SPLIT
For the matrix division is evaluated after the initiation of the matrix failure. If a matrix failure is triggered upon detection of matrix division, the element is marked for deletion. The division is determined using the following criteria:
in which α a scaling factor calculated based on the unidirectional matrix failure criterion, ψ.m, is. θ represents a user-defined limit value when triggering element deletion. The default value of θ is 0.75. θ must be in the range 0 < θ ≤ 1. Only the components σ22c, σ12c and σ13c the composite material tension are used in the pitch evaluation. These are the stress components that contribute to the longitudinal division in the matrix. The Macaulay brackets around the set σ22c make sure that σ22c only contributes to the evaluation of the matrix division when the tension is stressed.
Consider the following example where an item should be deleted when dividing with the limit θ = 0.80 is identified.* MATERIAL, NAME = IM7_8552 * ELEMENT DELETION, TYPE = MATRIX, CRIT = SPLIT 0.8
TYPE = FIBER, CRIT = ANY
For TYPE = FIBER, ANY is the only available criterion. The ANY criterion indicates that every fiber failure automatically triggers the deletion of the element. There are no data lines for this criterion.
Important Considerations About Immediate Degradation vs. Energy-Based Degradation
Element deletion takes place in different ways, depending on the decay scheme used. With immediate degradation, the deletion criteria for the element are monitored immediately at the start of the failure. With energy-based degradation, the deletion criteria for the element are only monitored when the breaking energy has been completely dissipated.
The following combinations of TYPE and CRIT are available for woven composites:* ELEMENT DELETION, TYPE = FIBER, CRIT = ANY * ELEMENT DELETION, TYPE = FIBER, CRIT = BOTH * ELEMENT DELETION, TYPE = FIBER, CRIT = RELOAD
For woven composites, element deletion criteria based on matrix failure are not available.
With CRIT = ANY, the deletion of an element is triggered if the fibers in a yarn fail.
With CRIT = BOTH, the deletion of an element is triggered if the fibers in both yarns fail.
With CRIT = RELOAD, the tensions in the yarn direction are monitored after a fiber failure. The normal tension in the failed thread direction, σn, with the maximum tensile strength in the failed yarn direction, S11u, compared. Exceeds the ratio of σn to S11U a custom value β, the element is deleted. β must be specified in the first data line after the keyword. Example:* ELEMENT DELETION, TYPE = FIBER, CRIT = RELOAD 0.3
In this example the element is deleted when σn 30% of S11U is or exceeds. The RELOAD criterion also includes the logic of the BOTH criterion, so that a fiber failure in both yarns would also trigger the deletion of the element.
The deletion of cohesive elements is only controlled by the keyword. The cohesive element is marked for deletion when the damage is fully accumulated (SDV6 = 1). No HIN keyword is required to delete cohesive elements.
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