Dynamic observation of impact phenomena is extremely important for designing automotive and armored structures. A dynamic moire interferometer has been developed at the INEL to image surface dispacement fields generated by dynamic loading events. A pulsed ruby laser is used to provide sufficient intensity to allow the imaging of displacement fields in periods of 20 ns. An electro-optic Q-switching system has been designed using standard electronic and optical components to pulse the ruby laser at rates of up to 1Mhz. In order to capture images, a Cordin high speed framing camera was integrated into the system.The dynamic moire interferometer produces fringe frields of in-plane displacement data, similar to the fringe data captured in dynamic holography or dynamic photoelasticity. Dynamic loading events generate moving fringe fields which reduce the fidelity of acquired fringe fields. A dynamic fringe analysis similar to Neuman's analysis for dynamic holography and Daily's analysis for dynamic photoelasticity has been performed to quantify this effect for a moire interferometer. It has been determined that the contrast of the fringes depends not only on the pulse duration of the laser and transience of the fringe field, but also on the frequency of the fringe field. This analysis has been used to interpret fringe data obtained from short duration stress pulses travelling through laminated carbon-fiber epoxy composites.

Processing-induced residual strains in solid cylinders of Nickel 200 were investigated using phase shifting moiré interferometry. Two different experimental approaches were used to study the strains produced during Tungsten-inert gas spot welding. A comparison of results for a ‘hot/fast’ and a ‘cool/slow’ weld demonstrate the capabilities of the general approach. Both experimental methods revealed distinct differences in the residual displacement and strain fields between the two types of welds.

The work is part of the rock mechanics effort for the Yucca Mountain Site Characterization Program. The laboratory-scale experiments are intended to provide high quality data on the mechanical behavior of jointed structures that can be used to validate complex numerical models for rock-mass behavior. Frictional sliding between simulated rock joints was studied using phase shifting moire interferometry. A model, constructed from stacks of machined and sandblasted granite plates, contained a central hole bore normal to the place so that frictional slip would be induced between the plates near the hole under compressive loading. Results show a clear evolution of slip with increasing load. Since the rock was not cycled through loading- unloading, the quantitative differences between the three data sets are probably due to a ``wearing-in`` effect. The highly variable spatial frequency of the data is probably due to the large grain size of the granite and the stochastic frictional processes. An unusual feature of the evolution of slip with increasing load is that as the load gets larger, some plates seem to return to a null position. Figs, 6 refs.

Strain development in several notched ceramic-matrix composites (CMCs) has been monitored over a broad range of load. This was achieved by using phase-shifting moire interferometry, which provides a map of the surface strains. A sequence of fringe patterns was used to chart the evolution of strain redistribution as a function of load. The ensuing strains were related to the micromechanical damage mechanisms. Stress concentrations were estimated from the strains by using stress/strain curves. Implications for the notch sensitivity of CMCs are discussed.

Understanding the mechanical behavior of jointed-rock masses is of critical importance to designing and predicting the performance of a potential nuclear waste repositiry. To this end we have studied the frictional sliding between simulated rock joints using phase shifting moire interferometry. Preliminary calibration models were made from stacks of Lexan plates that were sand-blasted to provide a uniform frictional interface. Load was applied monotonically and phase shifted moire fringe patterns were recorded at three different load states. Plots of slip along the interfaces for the model are presented to demonstrate the ability of the photomechanics technique to provide precise measurements of in-plane displacement, and ultimately the slip between the plates.

There is a great deal of interest in characterizing the dynamic mechanical behavior of laminated carbon-fiber/epoxy composites for military and aerospace applications. Current research efforts have been directed at measuring the strength lost because of accumulated damage. Very little work has been done to determine how this damage is accumulated during dynamic mechanical loading. Of particular interest is the effect of short duration (< 1 {micro}s) stress pulses on mechanical behavior such as delamination. In this paper, a magnetic flyer plate apparatus is presented for generating a short duration stress pulse in a unidirectional carbon-fiber/epoxy laminated composite. The stress pulse is characterized using a dynamic moire interferometer.

An important aspect of determining the suitability of Yucca Mountain as a possible nuclear waste repository requires understanding the mechanical behavior of jointed rock-masses. To this end we have studied the frictional sliding between simulated rock joints in the laboratory using the technique of phase shifting moire interferometry. The models were made from stacks of Lexan plates and contained a central hole to induce slip between the plates when the models were loaded in compression. These preliminary results confirm the feasibility of the approach and show a clear evolution of slip as function of load.

Experimental displacement and strain fields are presented for a generalized plane stress tensile specimen consisting of commercially pure titanium diffusion bonded to 6Al-4V titanium. Plastic flow initiates at the intersection of the interface with the specimen free edge. Further deformation results in concentrated shear bands emanating from the interface at both free edges. Interactions of the interface-free edge shear bands force a state of plane strain in the center of the specimen. These interface constraint effects have practical relevance on the testing of joined metals with property mismatch.

This article reviews the use of interferometric techniques to study composite material deformation under impulsive loading. Two techniques will be discussed in detail, moiré and holographic interferometry for both in- and out-of-plane motions. Recently developed lateral shearing interferometers will also be mentioned. The techniques will be reviewed from an information sampling viewpoint including the time domain as an additional bounding parameter, particularly in regards to the spatial resolution of the method and the amount of data that can be stored over an event. This article will begin with a brief review of the literature, progress to the techniques with applications and conclude with future directions that have applicability to industrial environments that require robust optical systems and data analysis techniques.

Moire interferometry is employed to study toughening in medium to large grain size nominally pure alumina. The fracture scale length, which is characterized by the grain size of the alumina, is systematically varied from 35 to 102 μm. R curves are derived from bulk mode I compliance calculations for the differing grain sizes and from the near tip moire fringes. The level of material toughening that arises from the nonsingular processes of crack bridging and grain boundary friction are found by comparing the bulk and near tip moire R curves.

An analysis on transformation toughening of magnesia partially stabilized zirconia (Mg-PSZ) is presented in this paper. Transformation toughening of Mg-PSZ is attributed to the stress induced phase transformation of tetragonal zirconia to monoclinic structure at the neighborhood of crack tip. A rate form constitutive model [13, 14], using a micromechanics approach, is employed. Stationary and stably propagating crack problems are analyzed, using finite element method. The results of finite element analysis are compared to those of experimental study of Perry et al. [12] (companion paper). In the comparison, it is found that displacement field and toughness enhancement during stable crack propagation predicted by the finite element analysis, are very analogous to those obtained in the experimental study.

Moiré interferometry is employed to study toughening in partially stabilized zirconia (PSZ). Energy to fracture as a function of crack growth curves (R-curves) is derived from mode I compliance calculations and from near tip fitting of the moiré fringes. The effect of the tetragonal to monoclinic phase transformation in the zirconia is found by comparing the bulk compliance R-curves to the locally derived moiré R-curve. Localized strain field plots are produced from the moiré data for the PSZ zirconia. The observed transformation zone height compares favorably with that predicted by Okada et al. [Acta metall. mater.40, 1421 (1992)] in a companion paper, as does the qualitative nature of the R-curve with predictions by Stump and Budiansky [Acta metall.37, 3297 (1989)].

Dynamic moire interferometry is employed to study the localized impact response of a thick composite plate. The plate, 15 mm thick by 50 mm wide by 152 mm in length, consists of 0/90/03 graphite fibers in a Hercules AS4/3501-6 carbon/graphite pre-preg. The plate is impacted under three-point bending. 1200l/mm gratings are replicated on the free plate edge directly under the impact site; a multiplication of two is used to obtain an in-plane displacement sensitivity of 0·4 mm. Displacements are interrogated approximately every 10 μs perpendicular to the 0° fiber direction. Initial results outline the localized displacement directly under the impact tup as a function of time. These displacements facilitate an understanding of the resistance of thick composite plates to damage from sharp impact.

An analysis of toughening of magnesia partially stabilized zirconia (Mg-PSZ) due to dilatational transformation is presented in this paper. Transformation toughening of Mg-PSZ is attributed to the stress-induced phase transformation of tetragonal zirconia to monoclinic structure in the neighborhood of a macro-crack tip. A trate (incremental) type constitutive model is developed, using a micromechanics approach, wherein the interaction between a transformed zirconia particle and the rest of the material is considered. Problems of stationary and stably propagating cracks are analyzed, using a finite element method. The results of finite element analysis are compared to those of an experimental study by Perry et al. In the comparisoon, of it is found that the displacement and toughness enhancement during stable crack propagation, predicted by the finite element analysis, are very analogous to those obtained in the experimental study. Moreover, the present constitutive model is capable of revealing detailed information, such as the distribution of transformed zirconia in the wake zone.

Elastic wave propagation fields for a stationary crack in an Izod fracture specimen have been investigated. Moiré interferometry was used to obtain the asymptotic cracktip displacement fields under Hopkinson bar loading at sampling rates on the order of 100 kHz. Mixed-mode stress-intensity factors as a function of time were extracted from the displacement data using local asymptotic extrapolation. Two-dimensional continuum finite elements were employed and agreement was found between actual experiment and two-dimensional computation.

At certain grain sizes, alumina R curves have been shown to increase with crack growth. This phenomenon is in contrast to R curves for metals, which exhibit a steady-state plateau effect with increasing crack growth. Recent results show R curves for calcium silicate geomaterials also increase. The specimen geometry employed for both alumina and geomaterials is a generalized plane stress double cantilever beam (DCB). The specimens are under direct pin loading with fixed displacement. This note will discuss the common mechanisms of increasing R curve behavior of these quasi brittle materials. Finally, a hypothesis on the discrepancy between the fracture toughness of single crack rock samples and in large seismic events is presented.

A combined Tardy and photoelastic fringe multiplication methodology is reviewed for three-dimensional stress freezing photoelasticity. Specifically, the investigation concerns the thin transitional region near the free surface-crack front intersection in a finite body. The photoelastic data are combined with moiré interferometry to provide stress and displacement fields surrounding a crack tip. Experimental methodology involving refined thin slicing techniques, enhanced photoelastic fringe constant determination and photoelastic data interpretation is presented.