Composite machining damage quantification using thermoelastic stress analysis

Abstract

A new experimental method is presented for quantifying machining damage in polymer matrix composites. The method consists of capturing infrared images of machined samples and using thermoelastic stress analysis to quantify damage from the machining event. A modified stress concentration factor is presented as an easily measured and useful damage parameter. Circular holes were drilled into the center of plate specimens fabricated from a commercially available glass fiber reinforced composite. A standard drill bit, brad point drill bit, and abrasive water jet machining were the three machine tools investigated. Infrared images were used to quantify the machining damage by assigning a thermoelastic stress analysis based stress concentration factor (mSCF) to each machined hole. The mSCF was then used to rank the damage inherent to each machining method. Optical and electron microscopy were utilized to identify the types of damage associated with the three machining methods. Finally, each sample was fatigued to failure to substantiate the IR results. The ranking of damage based upon the mSCF was in good agreement with the fatigue lifetime rankings: higher mSCF is associated with shorter fatigue lifetimes.

Analytical and experimental investigation of the effects of the machining processes on the mechanical behaviour of carbon epoxy composite laminates

“…Water-jet velocity can also be increased by reducing the orifice diameter together with sufficient abrasive flow rate [71]. Horn G.P et al [25] used a garnet abrasive of eightymesh size (177 µm) with water-jet pressure of 290 MPa. The polymer matrix composite specimen of length 152 mm, width 25 mm, thickness 2 mm and 6 mm hole diameter was tested at a stress ratio of 0.1 and a frequency of 2 Hz.…”

“…[57,58]. Both these criteria were calculated by Whitney and Nuismer from Lekhnitskii's Equation (25). The PSC assumes that failure occurs when the normal stress at some distance away from the circular hole, d o , is equal to or greater than the unnotched laminate tensile strength or the tensile strength σ f of the material.…”

“…Waterjet cutting is widely used in the machining of composites as it has good preconditions for cutting composite laminates and also reduces the problems made by CM process [12]. It is well known that a machined surface produced by AWJM is free from abnormalities like thermal or nonthermal stresses along the cutting path [22], matrix degradation, fiber pull-out and delamination [22][23][24] as a low thrust force is produced during this technique [25]. It also eliminates secondary finishing process [22][23][24].…”

An analytical method for predicting damage zone in orthogonal machining of unidirectional composites

“…Damage in composites is defined as either fiber breakage or matrix shearing, where fiber chipout may occur as the result of excessive normal stress in a fiber, and as a result of this damage load transfer in the vicinity of the broken fibers will not be as effective, and the local material properties deteriorates and will be significantly different from the bulk material properties. 12 Matrix shearing causes the surrounding fibers to become loose and unable to transfer mechanical loads.…”

Stress Redistribution in Ceramic Matrix Composites

“…Recent work at UIUC has utilized TSA to provide thermoelastic stress maps of impact-damaged composites to assign a stress concentration factor to the impact site. [10] The methodology is amenable to in-situ inspection of structural components and provides an objective, quantitative assessment of damage. Typical optical and TSA images of impact-damaged glass/epoxy and glass/polyurethane composites are shown in Figure 8.…”