Jutima Simsiriwong

Effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK).

In this study, the effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK) was investigated. Due to the versatility of its material properties, the semi-crystralline PEEK polymer has been increasingly adopted in a wide range of applications particularly as a biomaterial for orthopedic, trauma, and spinal implants. To obtain the cyclic behavior of PEEK, uniaxial fully-reversed strain-controlled fatigue tests were conducted at ambient temperature and at 0.02 mm/mm to 0.04 mm/mm strain amplitudes. The microstructure of PEEK was obtained using the optical and the scanning electron microscope (SEM) to determine the microstructural inclusion properties in PEEK specimen such as inclusion size, type, and nearest neighbor distance. SEM analysis was also conducted on the fracture surface of fatigue specimens to observe microstructural inclusions that served as the crack incubation sites. Based on the experimental strain-life results and the observed microstructure of fatigue specimens, a microstructure-sensitive fatigue model was used to predict the fatigue life of PEEK that includes both crack incubation and small crack growth regimes. Results show that the employed model is applicable to capture microstructural effects on fatigue behavior of PEEK.

Vibration testing of a carbon composite fuselage

This paper describes the details of an experimental investigation focusing on the vibration characteristics of a composite fuselage structure of an ultralight unmanned aerial vehicle (UAV). The UAV has a total empty weight of 70.3 kg and 6.3 m in length. The fuselage structure consists of the fuselage body with an integrated vertical stabiliser. All structural components are fabricated from oven-cured laminated carbon composite materials using uniaxial and biaxial prepreg fabric. The modal characteristics of the fuselage structure are determined for a free-free configuration which is simulated by suspending the structure from its wing attachment points through the use of springs. A centrally located shaker system is used to induce vertical oscillations in the structure, which is instrumented with nineteen dual axis accelerometers. Dynamic properties such as the frequency, damping and associated mode shapes are obtained for aeroelastic analysis. The design and implementation of the vibration tests along with the experimental results are presented.

Master Creep Compliance Curve for Random Viscoelastic Material Properties

The objective of this study is to apply the time-temperature superposition principle (TTSP) to the viscoelastic material functions that exhibit a large degree of variability to predict the long-term behavior of a vinyl ester polymer (Derakane 441–400). Short-term tensile creep experiments were conducted at three temperatures below the glass transition temperature. Strain measurements in the longitudinal and transverse directions were measured simultaneously using the digital image correlation technique. The creep compliance functions were characterized using the generalized viscoelastic constitutive equation with a Prony series representation. The Weibull probability density functions (PDFs) of the creep compliance functions were obtained for each test configuration and found to be time and temperature dependent. Creep compliance curves at constant probabilities were obtained and used to develop the master curves for a reference temperature of 24 °C using the TTSP.

Experimental Vibration Analysis of a Composite UAV Wing

This article describes the details of an experimental investigation focusing on vibration characteristics of a carbon composite ultralight unmanned aerial vehicle (UAV). Modal characteristics of the UAV wings are obtained and compared for two separate configurations: (1) wings mounted on the suspended aircraft to simulate a free-free arrangement and (2) a single wing mounted vertically in a fixture to test in a shaker-table approach. All structural components are fabricated from oven-cured laminated carbon composite materials using uniaxial and biaxial prepreg fabric. Multiple dual-axis accelerometers on the wing structure are used to determine the dynamic properties.

Viscoelastic Creep Compliance Using Prony Series and Spectrum Function Approach

The objective of this study is to compare the viscoelastic material property of a vinyl ester (VE) resin using (1) the generalized 3-D viscoelastic constitutive equation with a Prony series representation and (2) a spectrum function model. The Prony series representation of the Generalized Kelvin model (GKM) is used to determine the Prony series coefficients through the linear least squares (LSQ) method. The Elastic-Viscoelastic Correspondence Principle (EVCP) and the Laplace transform are used in the spectrum function approach, which utilizes a carefully selected distribution function that has the potential to describe a wide range of materials. Short-term unidirectional tensile creep experiments are conducted at two stress levels and at four temperatures below the glass transition temperature of the VE polymer. Experimental strains in both the longitudinal and transverse directions and the applied stress are measured using the digital image correlation (DIC) technique. The measured data is subsequently used to determine the creep compliance function for each test configuration. The potential and limitations of each modeling approach are discussed.

Data demonstrating the effects of build orientation and heat treatment on fatigue behavior of selective laser melted 17-4 PH stainless steel.

Axial fully-reversed strain-controlled (R=−1) fatigue experiments were performed to obtain data demonstrating the effects of building orientation (i.e. vertical versus horizontal) and heat treatment on the fatigue behavior of 17–4 PH stainless steel (SS) fabricated via Selective Laser Melting (SLM) (Yadollahi et al., submitted for publication [1]). This data article provides detailed experimental data including cyclic stress-strain responses, variations of peak stresses during cyclic deformation, and fractography of post-mortem specimens for SLM 17–4 PH SS.

Fatigue Behavior and Modeling for Thermoplastics

In this study, the cyclic behavior and the microstructure under cyclic loading of a semi-crystalline thermoplastic polyether ether ketone (PEEK) are investigated. Macroscopic strain life experiments under uniaxial loading condition were conducted at strain amplitudes ranging from 0.02 mm/mm to 0.04 mm/mm and at ambient temperature. Scanning electron microscopy (SEM) analysis was performed on fatigue specimens to examine crack incubation sites and microstructural inclusions responsible for incubating fatigue cracks. Other microstructural inclusion properties including inclusion type (pore or particle), inclusion size, and nearest neighbor distance of inclusions were also obtained. Based on the experimental results, the strain-based fatigue model was employed to obtain strain-life fatigue properties and e-N fatigue curves of PEEK.

A Statistical Formulation for Master Modulus Curves of a Vinyl Ester Polymer

ABSTRACT Master modulus curves are developed for a vinyl ester polymer with variability in its material properties. Tensile creep strains were obtained at three temperatures below the Tg through digital image correlation. A spectrum function was used to represent the viscoelastic strain response and modulus. A two-parameter Weibull distribution was used to characterize the probability distribution of the longitudinal modulus. The Weibull probability density functions of the viscoelastic modulus were obtained for each test configuration and found to be time and temperature dependent. Longitudinal modulus curves at constant probabilities were used to develop the master curves using the time–temperature superposition principle. GRAPHICAL ABSTRACT

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress–strain responses for each cycle, and the hysteresis stress–strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given.

Fatigue Modeling for Polyether Ether Ketone (PEEK) With Mean Strain Effects

In this study, the fatigue behavior of a polyether ether ketone (PEEK) polymer was investigated under uniaxial strain-controlled conditions with and without mean strain. Experimental study included a series of fully-reversed fatigue tests at five strain amplitudes (2%, 2.5%, 3%, 3.5%, and 4%) and fatigue tests at three mean strain values (2%, 2.5%, and 3%) at various frequencies. Stress responses of PEEK obtained from the tests under fully-reversed cyclic loading condition indicated a significant cyclic softening, while a stress relaxation was observed for the PEEK specimens under mean strain cyclic loading. Two different types of fatigue models, including a strain-based (Coffin-Manson) and energy-based, were employed to correlate fatigue life obtained from all experimental data. Among the two fatigue models, the fatigue life prediction using the energy-based approach was found to provide a better correlation to PEEK experimental data for both fully-reversed and mean strain conditions when compared to the Coffin-Manson model.Copyright