PSI - Issue 52

A.D. Cummings et al. / Procedia Structural Integrity 52 (2024) 762–784 A. Cummings / Structural Integrity Procedia 00 (2023) 000–000

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correlates K mat to a deeply cracked Compact Tension (CT) specimen. To account for low constraint conditions in the assessments, the K mat estimate can be increased to K c mat by calculating a parameter called T-stress, and providing the T-stress value is negative, K c mat is calculated by adjusting the T 0 reference temperature, using Eqn N.22 in Annex N BS7910 (2019):-

K c mat = 20 + ( K mat − 20) exp 0 . 019 −

10

T − stress

(10)

K I , T-stress, L r and σ ref can also be obtained with static cracked body FEA models based on the assumption that inertial e ff ects at the crack tip are negligible. In this study this is considered a reasonable assumption because the size of the flaws assessed are very small by comparison to the size and thickness of the package body.

5. Selected results from the drop orientation study

As an example of the approach, the base down drop orientation is considered. The study included the e ff ects of rigid internal contents of maximum payload, initially positioned at the lid which maximises travel into the base. This provides a bounding argument for interchangeable contents, negating any requirement to revisit the safety assessment for alternative, future usage cases of the 1647B. Fig. 3 shows the locations of the stress classification lines selected to characterise the stresses in the base. The red dots indicate the location of elements selected to write out stress time histories.

Fig. 3. Location of stress classification lines (SCLs). Red dots indicate elements selected in the base for time history post-processing

Fig. 4 shows the elastic stress time histories from which a t f = 100 µ s was estimated from the stress pulse. This is conservatively used to derive a dynamic K mat because any plasticity would increase the stress pulse duration and therefore the duration of t f , which improve the value of K mat . The time histories show that the first base mode of vibration at 4000 Hz, is excited due to the dynamic impact forces. This occurs independently to the interaction with the rigid contents. The initial peak at 200 µ s results in the bending mode of vibration, the outer surface is most highly stressed, with a peak (element) principal stress value of 797 MPa. A secondary impact occurs after 3.5ms when the rigid contents strike the base. This produces similar stress response in the base outer surface but also introduces a large peak (elastic) stress in the base internal radius of 1392 MPa, see Fig. 4b.