This study aims to correlate a newly proposed local time-dependent indicator of the damage accumulation in a thermoplastic laminate matrix with the degradation of the mechanical properties of the material as a whole. The material tested here is a carbon fiber–reinforced plastic used in the aircraft industry. Isothermal fatigue transient tensile loading and three-point bending are used for full-scale tests. The results of fatigue pulsating tension loading of the laminate are presented together with the outcomes of nondestructive measurements of the residual stiffness of the laminate. Local elastic and time-dependent properties of the laminate matrix, used as nondestructive indicators of the degradation of the matrix caused by repeatedly applied loads, are compared with the full-scale outcomes. The results confirm that the microindentation technique applied to the laminate matrix can be a suitable method for assessing the influence of fatigue tensile loading on the basic and time-dependent properties of the laminate.

The aim of the research presented here was to assess the influence of climatic loading on the basic mechanical properties of polymer sealants, from the viewpoint of their application in creating and repairing outdoor mosaics. Six promising sealants were selected for the measurements. They were tested in their native state and also after four different model types of physical-chemical ageing were applied. We used a combination of ultra-violet radiation with the influence of enhanced temperature, moisture and also soaking in water and freezing. The Hysitron TI 750D TriboIndeterTM system, equipped with a Berkovich indenter, was used for tests. The basic mechanical characteristics were measured using the Basic QS Trapezoid quasi-static mode. Time-dependent properties of the sealants were assessed by the indentation creep method. The results have confirmed that microindentation technique offers a suitable methodology for assessing changes in the basic mechanical time-dependent properties of the tested sealants due to photo-degradation processes and climatic effects.

The short-term instrumented microindentation technique was applied for assessing the influence of temperature in the glassy region on the time-dependent mechanical properties of an average epoxy resin mix near to its native state. Linear viscoelasticity theory with the assumption of time-independent Poisson ratio value forms the basis for processing the experimental results. The sharp standard Berkovich indenter was used to measure the local mechanical properties at temperatures 20, 24, 28, and 35 °C. The short-term viscoelastic compliance histories were defined by the Kohlrausch–Williams–Watts double exponential function. The findings suggest that depth-sensing indentation data of thermorheologically simple materials influenced by different temperatures in the glassy region can also be used, through the time-temperature superposition, to extract viscoelastic response functions accurately. This statement is supported by the comparison of the viscoelastic compliance master curve of the tested material with data derived from standard macro creep measurements under pressure on the material in a conformable state.

This paper aims to apply time-temperature superposition to short-term microindentation data measured at different temperatures, and to compare the viscoelastic compliance master curve that is found with data derived earlier from standard macro creep measurements in pressure. Using a sharp standard Berkovich indenter a successful application of this geometry in characterizing time-dependent mechanical properties of viscoelastic materials is confirmed.

The paper is aimed at an assessment of influence of damage accumulation in a thermoplastic/carbon laminate during a tensile cycling loading on durability, Young modulus and both instant and time-dependent local mechanical characteristics of a thermoplastic matrix, analysed by means of instrumented microindentation. Standard mechanical data from three-point bending are compared with results of the local microindentation testing.

This work aims to apply the microindentation technique for assessing the influence of two aging factors-long-term weathering and long-term laboratory aging-on the time-dependent mechanical properties of an epoxy composition. The linear theory of viscoelasticity was taken as a background for the problem, and the time-independent Poisson ratio value was assumed to simplify the assessment. Two nano/microindenters were used (Hysitron Triboscan and Nano XP Indenter) at two different laboratories. Four special time-dependent loading histories were applied: indentation under a step load, indentation under a constant load rate, indentation with a fixed depth of penetration, and indentation under a constant rate of penetration. The short-term histories of the viscoelastic compliance of a common epoxy composition, affected by 5-year weathering or laboratory aging, measured using a microindentation technique were compared to the data derived from standard macro measurements. The findings suggest that a qualitative assessment of the influence of the investigated aging effects on mechanical properties can be handled using short-term microindentation data, but the data has to be freed of possible attendant factors, especially of the influence of polishing procedures accompanying the microindentation techniques, before comparing it with standard measurement data. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2090-2094, 2012

This paper reports on a micro- and nano-indentation investigation of iPP filled with multiwall carbon nanotubes (MWCNT) in the range of 0.1-3 wt.%. Vickers microhardness and Total microhardness were determined using a mhp-150 microhardness tester and a NU-2 light microscope. Elastic modulus, instantaneous compliance and hardness were obtained using an XP Nano Indenter. It was established that a small weight fractions of MWCNT (0.1 wt.%) significantly improves the microindentation parameters. A comparison of the results of the two measuring techniques showed a relatively large difference in hardness values. This may be related to the different physical nature of the measured microhardness characteristic. There is a discussion presented of the similarity and/or difference in the microhardness values from the viewpoint of the trend of concentration dependencies and also their physical peculiarities.

This paper reports on the time-dependent recovery process in a local part of a quasi-homogeneous and quasi-isotropic viscoelastic hemisphere after microindentation unloading. After contact between a Vickers indenter and a viscoelastic material comes to an end, the recovery progression is monitored using a microscope equipped with an interferometer, and a record is made using a digital camera. The histories of the depth of the indentation and the changes in the indented area are defined. Using an approach involving direct microindentation measurements of viscoelastic properties, the viscoelastic recovery creep compliance is determined and its values are compared with the creep compliance measured by the standard macro creep method, and with the creep compliance derived from instrumented microindentation.

Under accepted simplifications about the linear viscoelastic background of the problem and the time-independent value of the Poisson’s ratio, this paper aims to compare the short-term histories of the viscoelastic functions of a common time-dependent material, e.g. viscoelastic compliance and relaxation modulus measured using a microindentation technique, with data derived from standard macro measurements. Two nano/microindenters were used (Hysitron Triboscan and Nano XP Indenter) at two different laboratories. Four special time-dependent loading histories were applied: indentation under a step load, indentation under a constant load rate, indentation with a fixed depth of penetration and indentation under constant rate of penetration. The goal of the study is to assess the potential of this approach.

It is known that the durability of materials is related to the conditions under which they are exploited, including the loading that they undergo. The material “durability-constant load” relation is known as Creep-Rupture Strength (CRS). It takes a long time to determine CRS experimentally, and it proves to be expensive. In this paper we check a method for predicting CRS under tension that employs data from short term tests. The results for loading under tension are compared with results for the same material subjected to bending.

The effect of a particle marble filler on the creep response of a crosslinked polyester matrix before and after physical aging is described. Composites with various filler-polyester matrix percentages are prepared by applying mixing technology, curing at room temperature, and post-curing above the glass-transition temperature. Two groups of specimens of identical composition are studied. The first group is tested 1 month after preparation (relatively nonaged), whereas the second group is tested after 13 years of storage at stable room temperature and humidity, at current atmospheric pressure, and in the absence of direct light (aged). The two groups of specimens (aged and nonaged) are subjected to creep measurements. The modulus of elasticity and the creep compliance are determined, plotted against the filler volume fraction, and fit by empirical equations. A simple mechanical model is proposed to fit the compliance curves, and good agreement between the measured and predicted values is shown. The mechanical behavior of the composites is also described, using empirical equations that fit the relation between the composite/matrix ratio of the deformation characteristics and the filler volume fraction. A crucial matrix influence is proposed to fit the compliance curves, and good agreement between the measured and predicted values is shown. Experimentally established natural regularities can be used to predict the creep compliances of composites from a less demanding experimental program. (C) 2003 Wiley Periodicals, Inc.

The replacement of the standard replication technique by gluing the pre-embossed foil grating for the use in moire interferometry is the concern of the article. The manufacturing of the pre-embossed foil diffraction grating is explained. Relations of the influence of the specimen surf-ace profile to the zero interference field are derived. Some measurements of the profile of glued grating are shown including calculated extraneous interference field. Example of moire interferogram is shown using glued foil grating.

A method is presented for the process of elimination of the influence of ellipticity of interfering waves in moire interferometry, using a combination of an analytical solution and direct measurements of ellipticity parameters of each interfering wave. The method is advantageous in that it makes it possible to access and overcome the unfavorable influence of ellipticity. The phase difference of interfering waves is described. A model case is used to show the influence of wave ellipticity and the fluctuation of light source output on the mean irradiation intensity of the interference field, visibility of fringes, and the error of the phase function determination. (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(99)00604-2].

An analysis is provided for the continuous relaxation and retardation spectra of epoxy matrix composites filled with different amounts with marble micro-particles. The particle size distribution is characterized by the diameter sampling medium d 50 = 13 μm and the sampling quantile d 97 = 80 μm. The concentration of this filler was 10, 29 and 44.5 vol%. The creep compliance and the relaxation modulus were determined from experimental results. Alfrey's method is used to define the continuous spectra from these long-term (10 3 days) creep and stress relaxation data. A polynomial approximation is applied to the analytical form of the results. The influence of the filler fraction on the spectra's distribution and on the equilibrium values of relaxation moduli and creep compliances is discussed. The application of discrete relaxation and retardation spectra and the mutual transition between them are demonstrated using a Laplace transform.

Long-term (More than 20 years) creep under compression of two polymer concretes, polyestermalein resin/mineral filler composites, was studied. The concretes differ with diabase filler size (d=5–10 mm and d=10–20 mm). It was shown that nonlinearity of viscoelastic properties of concrete increases as the size of filler particle decreases. Aging of the polymer concretes reduces their viscoelastic compliance and shortens the time interval necessary to reach equilibrium conditions under stable loading state.