Fatigue behavior and lifetime distribution of impact-damaged carbon fiber/toughened epoxy composites under compressive loading

Abstract

This paper presents fatigue lifetime data of impact-damaged carbon fiber/toughened epoxy composites under compressive loading to elucidate the lifetime prediction methodology based on statistical approaches. Drop-weight impact damage was induced to a composite specimen with impact energy of 6.7 J/mm in accordance with ASTM D7136. Postimpact fatigue tests were conducted using a test fixture defined in ASTM D7137 under compression-compression loading (R = 10) at room temperature. The maximum compressive stress (S min ) was 200, 210, 220, 230, and 240 MPa, and the total number of specimens was 31. The compression-after-impact strength and fatigue lifetime show considerable scattering. This result is apparently derived from the variation in impact damage size. A simple statistical model based on the weakest link theory was proposed for predicting the lifetime of impact-damaged composite laminates. Results show that the experimentally obtained data were confirmed consistently using this model. The ratio between the endurance limit at 10 6 and 10 7 cycles and the initial static strength was estimated as 0.74 and 0.68 as B-basis allowable values.

The fatigue of carbon fibre reinforced plastics - A review

“…Comparing post impact damaged composites under tension-compression (T-C) and compression-compression (C-C) fatigue, Mitrovic and co-workers reported almost no difference in T-C damage mode between the undamaged and impact-damaged composites, whereas C-C fatigue of impact-damaged composites at high stress levels (70-80%) revealed extensive damage evolution [111]. Melin and Schon [112] further stipulated the post-impact crack line follows the buckle in the CFRP material during compressive fatigue, while Ogasawara and co-workers [113] (using high strength T800S/3900-2B epoxy matrix CFRP) reported that in thick (32 ply) quasi-isotropic laminates [+45, 0, −45, +90, 0, 0] 4s , that post-impact compressive fatigue advances damage, but primarily within the boundaries of the impact-damaged region.…”

Tracking composite material damage evolution using Bayesian filtering and flash thermography data

“…Subsurface delaminations, along with flaws present from fabrication, may also grow over the lifetime of the part due to normal loads. [7][8][9] In this paper, we propose a process to utilize significantly more of the information available about a part over its lifetime in order to better estimate the state of the part. We propose a method where the lifetime flash thermography data is used in a Bayesian filter to track the damage state of a part.…”

State Tracking of Composite Delaminations with a Bayesian Filter

“…These materials, which are fabricated from layers of fiber in a cured matrix, may sustain damage that cannot be identified from surface inspection. Subsurface delaminations (areas where the layers of the composite have disbonded), along with flaws present from fabrication, may grow, due to normal loads, over the lifetime of the part [2]. Subsurface delaminations caused by impacts can result in a significant loss of load carrying capacity but leave little to no indication of damage on the surface at the point of impact or surrounding areas.…”