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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

A comparison of pure mode I and mixed mode I-III cracking of an adhesive containing an open knit cloth carrier

Static and fatigue tests were carried out on two commercial modified epoxy film adhesives with a wide open knit polyester carrier in order to compare crack resistance in mode I and mixed mode I-III loading. The carrier cloth is found to have a significant influence on the cracking behavior of the adhesives. The open air net carrier used in this study separates from the adhesive in mode I cracking but shreds during mixed-mode crack extension. This decreases the opening mode toughness but increases the mixed-mode toughness as compared with results obtained earlier using a heavier knit carrier. The results suggest that the type of carrier may have a far larger influence on crack resistance than is generally recognized.

Ripling, E. J.↗
DOE OSTI2018

Effect of Compressive Mode I on the Mixed Mode I/II Fatigue Crack Growth Rate of 42CrMo4

Subsurface cracks in mechanical contact loading components are subjected to mixed mode I/II, so it is necessary to evaluate the fatigue behavior of materials under mixed mode loading. For this purpose, fatigue crack propagation tests are performed with compact tension shear specimens for several stress intensity factor (SIF) ratios of mode I and mode II. The effect of compressive mode I loading on mixed mode I/II crack growth rate and fracture surface is investigated. Tests are carried out for the pure mode I, pure mode II, and two different mixed mode loading angles. On the basis of the experimental results, mixed mode crack growth rate parameters are proposed according to Tanaka and Richard with Paris’ law. Results show neither Richard’s nor Tanaka’s equivalent SIFs are very useful because these SIFs depend strongly on the loading angle, but Richard’s equivalent SIF formula is more suitable than Tanaka’s formula. The compressive mode I causes the crack closure, and the friction force between the crack surfaces resists against the crack growth. In compressive loading with 45° angle, da/dN increases as K{sub eq} decreases.

36 MATERIALS SCIENCE↗
NASA NTRS2003

Mode I, Mode II, and Mixed-Mode Fracture of Plasma-sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

The mixed-mode fracture behavior of plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings was determined in air at 25 and 1316 C in asymmetric four-point flexure with single edge v-notched beam (SEVNB) test specimens. The mode I fracture toughness was found to be K(sub Ic) = 1.15 plus or minus 0.07 and 0.98 plus or minus 0.13 MPa the square root of m, respectively, at 25 and 1316 C. The respective mode II fracture toughness values were K(sub IIc) = 0.73 plus or minus 0.10 and 0.65 plus or minus 0.04 MPa the square root of m. Hence, there was an insignificant difference in either K(sub Ic or K(sub IIc) between 25 and 1316 C for the coating material, whereas there was a noticeable distinction between K(sub Ic) and K(sub IIc), resulting in K(sub IIc) per K(sub Ic) = 0.65 at both temperatures. The empirical mixed-mode fracture criterion best described the coatings' mixed-mode fracture behavior among the four mixed-mode fracture theories considered. The angle of crack propagation was in reasonable agreement with the minimum strain energy density criterion. The effect of the directionality of the coating material in on K(sub Ic) was observed to be insignificant, while its sintering effect at 1316 C on K(sub Ic) was significant.

Choi, Sung R.↗
NASA NTRS1985

Characterization of mode 1 and mixed-mode failure of adhesive bonds between composite adherends

A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

Mall, S.↗
NASA NTRS1986

Characterization of mode I and mixed-mode failure of adhesive bonds between composite adherends

A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

Mall, S.↗
NASA NTRS1985

Characterization of Mode I and mixed-mode delamination growth in T300/5208 graphite/epoxy

The roles played by Mode I and Mode II strain-energy release rates (G-I and G-II, respectively) in inducing delamination growth under static and fatigue loading were investigated, using T300/5208 graphite/epoxy specimens. Double cantilever beam (DCB) specimens and cracked lap shear (CLS) specimens were used for pure Mode I and mixed-mode tests, respectively. Fatigue-induced delamination growth was characterized by constant-amplitude fatigue tests at a minimum to maximum cyclic load ratio of 0.05 and a frequency of 10 Hz. During the tests, the maximum and minimum strain-energy release rates (Gmax, Gmin) and the delamination growth rate (da/dN) were monitored. Static tests on mixed-mode CLS specimens measured the total strain-energy release rate, which was broken into G-I and G-II components using finite-element analysis. A power-law relationship between da/dN and G-Imax, and da/dN and Gmax were obtained from fatigue test results on DCB and CLS specimens, respectively. The power law for a pure Mode II delamination was derived from CLS results by subtracting the contribution due to G-I.

Ramkumar, R. L.↗
NASA NTRS1986

Criterion for mixed mode fracture in composite bonded joints

A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite-epoxy composite adherends bonded with a toughened epoxy adhesive. The mode I, mode II and mixed mode I-II fracture energies of the tested adhesives were found to be equal to each other. The criterion for mixed mode fracture in composite bonded joints was found.

Mall, S.↗
NASA NTRS1986

Criterion for mixed mode fracture in composite bonded joints

A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite/epoxy (T300/5208) composite adherends bonded with a toughened epoxy (EC 3445) adhesive. The mode I, mode II and mixed-mode I-II fracture energies of the tested adhesive were found to be equal to each other. Furthermore, the criterion for mixed mode fracture in composite bonded joints was determined.

Mall, S.↗
DOE OSTI2020

High dynamic range CdTe mixed-mode pixel array detector (MM-PAD) for kilohertz imaging of hard x-rays

A hard x-ray, high-speed, high dynamic range scientific x-ray imager is described. The imager is based on the mixed-mode pixel array detector (MM-PAD) readout chip coupled to a 750 µm thick cadmium telluride (CdTe) sensor. The full imager is a 2 × 3 tiled array of MM-PAD sensor/readout chip hybrids. CdTe improves detection for high energy x-rays as compared to silicon sensors, enabling efficient x-ray imaging to extend to >100 keV. The detector is capable of 1 kHz imaging and in-pixel circuitry has been designed to allow for well depths of greater than 4 × 10 6 80 keV x-rays. Here, a charge integrating front-end allows for quantitative measurement of high flux x-ray images beyond the capabilities of photon counting detectors. Detector performance is summarized and experimental measurements are presented.

99 GENERAL AND MISCELLANEOUS↗
NASA NTRS1985

Interaction of mixed mode loading on cyclic debonding in adhesively bonded composite joints

A combined experimental and analytical investigation of an adhesively-bonded composite joint was conducted to characterize the fracture mode dependence of cyclic debonding. The system studied consisted of graphite/epoxy adherends bonded with EC 3445 adhesive. Several types of specimens are tested which provide the cyclic debond growth rate measurements under various load conditions: mode 1, mixed mode 1 to 2, and mostly mode 2. This study shows that the total strain-energy-release rate is the governing factor for cyclic debonding.

Mall, S.↗
NASA NTRS1985

Interaction of mixed mode loading on cyclic debonding in adhesively bonded composite joints

A combined experimental and analytical investigation of an adhesively-bonded composite joint was conducted to characterize the fracture mode dependence of cyclic debonding. The system studied consisted of graphite/epoxy adherends bonded with EC 3445 adhesive. Several types of specimens are tested which provide the cyclic debond growth rate measurements under various load conditions: mode 1, mixed mode 1 to 2, and mostly mode 2. This study shows that the total strain-energy-release rate is the governing factor for cyclic debonding.

Mall, S.↗
NASA NTRS1986

Effect of adherend thickness and mixed mode loading on debond growth in adhesively bonded composite joints

Symmetric and unsymmetric double cantilever beam (DCB) specimens were tested and analyzed to assess the effect of: (1) adherend thickness, and (2) a predominantly mode I mixed mode loading on cyclic debond growth and static fracture toughness. The specimens were made of unidirectional composite (T300/5208) adherends bonded together with EC3445 structural adhesive. The thickness was 8, 16, or 24 plies. The experimental results indicated that the static fracture toughness increases and the cyclic debond growth rate decreases with increasing adherend thickness. This behavior was related to the length of the plastic zone ahead of the debond tip. For the symmetric DCB specimens, it was further found that displacement control tests resulted in higher debond growth rates than did load control tests. While the symmetric DCB tests always resulted in cohesive failures in the bondline, the unsymmetric DCB tests resulted in the debond growing into the thinner adherend and the damage progressing as delamination in that adherend. This behavior resulted in much lower fracture toughness and damage growth rates than found in the symmetric DCB tests.

Mangalgiri, P. D.↗
NASA NTRS2008

Assessment of Crack Path Prediction in Non-Proportional Mixed-Mode Fatigue

Non-proportional mixed-mode loading is present in many systems and a growing crack can experience any manner of mixed-mode loading. Prediction of the resulting crack path is important when assessing potential failure modes or when performing a failure investigation. Current crack path selection criteria are presented along with data for Inconel 718 under non-proportional mixed-mode loading. Mixed-mode crack growth can transition between path deflection mechanisms with very different orientations. Non-proportional fatigue loadings lack a single parameter for input to current crack path criteria. Crack growth transitions were observed in proportional and non-proportional FCG tests. Different paths displayed distinct fracture surface morphologies. New crack path drivers & transition criteria must be developed.

Highsmith, Shelby, Jr.↗
NASA NTRS1993

A bilinear failure criterion for mixed-mode delamination

Many different failure criteria have been suggested for mixed-mode delamination toughness, but few sets of mixed-mode data exist that are consistent over the full range of Mode 1 opening load to Mode 2 shear load range. The mixed-mode bending (MMB) test was used to measure the delamination toughness of a brittle epoxy composite, a state-of-the-art toughened epoxy composite, and a tough thermoplastic composite over the full mixed-mode range. To gain insight into the different failure responses of the different materials, the delamination fracture surfaces were also examined. An evaluation of several failure criteria that have been reported in the literature was performed, and the range of responses modeled by each criterion was analyzed. A bilinear failure criterion was introduced based on a change in the failure mechanism observed from the delamination surfaces. The different criteria were compared to the failure response of the three materials tested. The responses of the two epoxies were best modeled with the new bilinear failure criterion. The failure response of the tough thermoplastic composite could be modeled well with the bilinear criterion but could also be modeled with the more simple linear failure criterion. Since the materials differed in their mixed-mode failure response, mixed-mode delamination testing will be needed to characterize a composite material. This paper presents consistent sets of mixed-mode data, provides a critical evaluation of the mixed-mode failure criteria, and should provide general guidance for selecting an appropriate criterion for other materials.

Reeder, James R.↗