PSI - Issue 77

Sunny O. Uguzo et al. / Procedia Structural Integrity 77 (2026) 521–528

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60 o C. Thus, TCP 1 transitioned between laminate dominated and liner dominated materials failures, never to buckling. TCP 2 with larger radius and same thickness still resulted in an enhanced global stability compared to the base TCP (see Figs. 4 and 5). At 4 o C, P cr was 6319kN (3.8 x Base) and the material failure load rose modestly from 1810kN to 2400kN. Like TCP 1 , material failure was dominant at all T i values, with matrix compression at low T i , matrix compression plus liner yield combination around 60 o C and inner liner yield at high T i (≥ 90 o C).

Table 5: Geometry definitions of investigated TCPs.

TCP Property Inner radius (r i ) Outer radius (r e ) Inner liner thickness Outer liner thickness Laminate thickness

Base TCP TCP 1

TCP 2

0.076m 0.114m 0.126m 0.1m 0.15m 0.15m 0.008m 0.012m 0.008m 0.008m 0.012m 0.008m 0.008m 0.012m 0.008m

Laminate fibre orientation [±55] 4

[±55] 4

[±55] 4

D/t

8.33

8.33

12.5

Fig. 5. Failure loads vs. T i for TCP 1 (left) and TCP 2 (right).

At elevated T i the inner liner was the weak link due to decline of the APC-2 PEEK yield strength with increased T i . Therefore, liner yield dominated despite thicker liners. Thicker liners enhanced the yield threshold but did not change the hierarchy of failure modes. For instance, at 120 o C, base TCP failed at 590kN, while TCP 1 failed at 1300kN. Enlarging diameter and thickness greatly enhanced the TCP stability, shifting designs from stability limited to material yield limited. Additionally, increasing TCP diameter alone often suffices to prevent global buckling within operational load considerations. However, high thermal gradients ultimately make liner yield decisive. Consequently, practical design improvements may require balancing added mass with strength/stability gains, while exploring higher temperature polymers or reinforced liners for better thermal robustness. 4. Conclusions This study deduced that TCP buckling capacity declined as internal surface temperature and thermal gradient rose, evidencing thermal softening. Failure analyses revealed failure mode transitions with temperature change. At low T i some laminates, such as [±55] 4 and[±65 2 /±75 2 ], buckled first, but beyond 60 – 90 o C all configurations became material limited, and by 120 o C inner liner plastic yielding was the dominant. This confirmed that the liner was the high temperature weak link. Furthermore, hybrid laminate TCPs that combine low and high angles, i.e. [±75 2 /±30 2 ] and [±55 2 /±30 2 ], best balanced high baseline P cr with modest thermal decay and retained higher material load bearing capacity at elevated T i . In contrast all high or mid angle layups, i.e. [±65 2 /±75 2 ] and [±55] 4 , were least attractive under steep thermal gradients. In addition, increasing diameter and wall thickness (TCP 1 ) or diameter alone (TCP 2 ) substantially raised P cr