Charge energy-dependent interlock and failure behavior of CFRP/Al E-SPR joints

Area of Science:

• Materials Science
• Mechanical Engineering
• Automotive Engineering

Background:

• Automakers seek lightweight materials like CFRP and aluminum for fuel efficiency.
• Joining dissimilar materials (CFRP/Al) presents challenges for conventional methods.
• Self-piercing riveting (SPR) is used, but electromagnetic SPR (E-SPR) offers advantages for high-velocity joining.

Purpose of the Study:

• To investigate the effects of charge energy on interlock and failure behavior in CFRP/Al joints formed by E-SPR.
• To evaluate suitable rivet-die geometries for E-SPR of dissimilar materials.
• To establish the relationship between charge energy, joint geometry, failure mode, and strength.

Main Methods:

• Utilized electromagnetic self-piercing riveting (E-SPR) with a C-type rivet and FM-type die.
• Systematically varied charge energy to influence rivet penetration and interlock formation.
• Analyzed cross-sectional dimensions, interlock distance, and failure modes.

Main Results:

• Interlock distance increased with charge energy, ranging from 0.18 to 0.65 mm.
• A transition in failure mode from pull-out to bearing failure occurred around 0.42 mm interlock.
• Excessive charge energy (≥5.5 kJ) caused CFRP damage, reducing joint strength despite increased interlock.

Conclusions:

• Charge energy significantly influences interlock distance and failure modes in E-SPR.
• Optimizing charge energy is crucial to prevent CFRP damage and maximize joint strength.
• E-SPR shows promise for joining CFRP/Al, but careful parameter control is needed.