This is similar to Phat, mesh exposion type event? - World Creation - Unreal Engine Forums, which has no answers.
Please see attached images - before and during selected simulation. Physics bodies exploding and badly stretching/deforming the mesh. Original default Phys set up did not, but could not be used for ragdoll.
Under 4.5 - driving me nuts. Tried making sure nothing overlaps - also the opposite, making everything overlaps (as they do in the tutorial btw). Switched on Disable collision on each pair. Switched on Enable Projection (setting Linear to zero in an attempt to stop any translation). Standard 3ds Max Biped. Bodies set up for Pelvis/Left thigh/Left Calf/Left Foot. To scaling of root (or any bone) etc. All Linear Limits set to locked. Angular limits as expected (mostly locked in one or two axis and limited else wise). All joints simulate selected (alone at their level in hierarchy) perfectly, but select all the bones (or for one higher in the hierarchy than leaf level) and everything below is stretched on simulate.
Example Settings:
Joint Name: Bip01_L_Thigh
Constraint Bone 1: Bip01_L_Thigh
Constraint Bone 2: Bip01_Pelvis
Disable Collision: Checked (tried both off and on)
Linear Limits: All Motion Axis set to Locked - Linear Breakable: Unchecked
Enable Projection: Checked (tried both off and on)
Projection Linear Tolerance: 0 (also tried default 0.5)
Projection Angular Tolerance: Left at default = 10
Angular Swing 1 Motion: Limited
Angular Twist Motion: Locked
Angular Swing 2 Motion: Limited
Swing 1 Limit Angle: 65
Swing 2Limit Angle: 25
Swing Limit Soft: Checked (default)
Swing Limit Stiffness: 50 (default)
Swing Limit Damping: 5 (default)
Angular Breakable: Unchecked (default)
Angular Break Threshold: 500 (default - grayed out)
Linear Motor: All unselected (default)
Angular Motor: All unselected (default)
[All other joints are the same except for Angular limits as expected]