Marinera, why should the penis never be stretched when erect? Just curious why exactly.
Because when erect most part of the pressure is on tunica albuginea:
A Three-Dimensional Model of the Penis for Analysis of Tissue Stresses during Normal and Abnormal Erection
ERAN LINDER-GANZ a , AMIT GEFEN a , DAVID ELAD a , AND JUZA CHEN b
a Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel b Department of Urology, Tel Aviv Medical Center, Tel Aviv, Israel
Here we developed a three-dimensional model for structural analysis of normal erection as well as erections of a penis with substantial asymmetry of the corporal bodies, and Peyronie's disease. The model was constructed based on anatomical images and included skin, tunica albuginea, corpus cavernosa, and spongiosum. The mechanical behavior of the tunica and skin were assumed to be three-dimensional-orthotropic, and other tissues as well as Peyronie's plaque was taken as linear elastic. Stresses and deformations during erection were analyzed using a commercial finite elements (FE) solver. Erection was simulated by raising blood pressure in the corporal bodies to 100 mmHg. The tunica was found to be the most highly loaded tissue in the erect penis. Peak von Mises stresses in the healthy tunica, tunica of the asymmetric corpora model, and tunica with Peyronie\’s disease were 114 kPa, 167 kPa, and 830 kPa, respectively. The angles of distortion of the penis with respect to the vertical axis were ∼4.5° and ∼2°, for the asymmetric and Peyronie's cases, respectively. The model's ability to determine internal stresses in the erect penis offers a new point of view on the mechanical factors involved with erection, and enables us to relate these data with different penile pathologies.
when the penis is erect, TA is thinner and less elastic; placing additional stress can easily lead to TA injuries:
Penile rupture or fracture is a rare injury. It involves a tear in the lining (tunica albuginea) of the corpora cavernosa. It characteristically occurs with trauma to the penis during an erection.