Masoud Yekani Fard

This presentation discusses macro-scale material testing. |

The compliance of the mixed-mode bending (MMB) test fixtures can influence the interlaminar fracture toughness measurements for different mixed-mode ratios in an unpredictable way. The purpose of this article is to introduce the improved mixed-mode bending (IMMB) apparatus with slight modifications to the current MMB apparatus and universally recognized by current standards. The MMB apparatus is used to measure any Mode I to Mode II strain energy release rate (SERR) ratio from 0 to approximately 5. The original MMB components were investigated using a finite-element optimization algorithm and an analytical model for exploring the relationship between the component’s stiffnesses and MMB compliance. Two IMMB designs are presented. The first design addresses MMB’s compliance by modifying the dimensions of the most impactful components. The second design introduces new components in addition to dimensional changes to maximally increase MMB stiffness. The new designs enhance the MMB apparatus’s stiffness by 27% and 87%, respectively.

In this study, overlapped biaxial and seamless twill carbon fiber pipes and vessels were manufactured. Steel pressure vessels were repaired with flexible twill and biaxial fabric. The pipes and vessels were subjected to hydrostatic pressure, internal cyclic pressure, postfatigue functional failure (FF) and burst pressure. Overlapped tubes with composite and metallic end caps experience premature FF at less than 50% of the theoretical pressure due to delamination. However, seamless tubes almost reached the theoretical pressure. Fatigue tests were applied to the tubes at stress levels of 45% and 75% FF pressure up to 9,000 cycles. Thin seamless tubes sustained the cyclic hydrostatic pressure at 45% of FF up to 9,000 cycles, while at 75% of FF some slight damage occurred. The overlapped tubes showed little damage at 45% FF after 9,000 cycles, but severe damage at 75% FF with an explosion. The fatigued seamless and overlapped composite tubes showed a maximum of 30% and 50% reduction of FF pressures. The reorientation of the flexible fiber tows in seamless vessels is the primary energy dissipation mechanism and avoids failure. The repaired pressure vessels experienced FF at 40% of the theoretical FF. The ASME boiler and pressure vessel equations safely predict the load-carrying capacity of the seamless tubes.

Enhanced Carbon Fiber Reinforced Polymers (CFRP) with nanoparticulate have been shown to impact performance in all modes of interlaminar fracture. The proposed experimentation in this study employed an advanced Atomic Force Microscopy (AFM) technique to investigate the relationship between interphase and mode I fracture properties. The interphase region is of vast importance to

Carbon fiber reinforced polymer composites (CFRPs) have been shown to exhibit superior mechanical properties over metallic alloys at a significantly lower density. For these reasons, CFRPs have been extensively integrated into aerospace, automotive, and energy generation sectors. The interphase region between the carbon monofilament and epoxy matrix is immensely vital to