Properties of five toughened matrix composite materials

The use of toughened matrix composite materials offers an attractive solution to the problem of poor damage tolerance associated with advanced composite materials. In this study, the unidirectional laminate strengths and moduli, notched (open-hole) and unnotched tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths of five carbon fiber/toughened matrix composites, IM7/E7T1-2, IM7/X1845, G40-800X/5255-3, IM7/5255-3, and IM7/5260 have been evaluated. The compression-after-impact (CAI) strengths were determined primarily by impacting quasi-isotropic laminates with the NASA Langley air gun. A few CAI tests were also made with a drop-weight impactor. For a given impact energy, compression after impact strengths were determined to be dependent on impactor velocity. Properties and strengths for the five materials tested are compared with NASA data on other toughened matrix materials (IM7/8551-7, IM6/1808I, IM7/F655, and T800/F3900). This investigation found that all five materials were stronger and more impact damage tolerant than more brittle carbon/epoxy composite materials currently used in aircraft structures

Failure analysis of CFRP laminates subjected to Compression After Impact: FE simulation using discrete interface elements

This paper presents a model for the numerical simulation of impact damage, permanent indentation and compression after impact (CAI) in CFRP laminates. The same model is used for the formation of damage developing during both low-velocity / low-energy impact tests and CAI tests. The different impact and CAI elementary damage types are taken into account, i.e. matrix cracking, fiber failure and interface delamination. Experimental tests and model results are compared, and this comparison is used to highlight the laminate failure scenario during residual compression tests. Finally, the impact energy effect on the residual strength is evaluated and compared to experimental results

Properties of three graphite/toughened resin composites

Results are presented from an experimental evaluation of IM7/977-2, IM7/F655, and T800/F3900. Data presented include ply-level (unidirectional laminate) strength and moduli, unnotched and notched (open hole) tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths. These data are compared with properties of other toughened (IM7/8551-7 and IM6/18081) and brittle (T300/5208) graphite-epoxy materials. The IM7/977-2, IM7/F655, and T800/F3900 materials are substantially stronger and more damage tolerant than widely used first generation composite materials such as T300/5208. The T800/F3900 outperforms IM7/977-2 and IM7/F655 materials in tolerance to projectile impacts. Compression-after-impact strengths were found to be dependent on impactor velocity for a given impact energy. The open hole compression properties of all three materials are degraded by the combination of heat and moisture

A numerical study on impact and compression after impact behaviour of variable angle tow laminates

Recent developments of variable angled tow (VAT) technology have indicated that variable stiffness composite laminates offer a strong potential for structural tailoring. However, the design complexity requires use of numerical analysis and novel techniques for this type of structural composites. This paper addresses the problem of the impact and compression after impact (CAI) behaviour prediction of variable stiffness composite laminates with emphasis on the effect of the interaction between fibre orientations, matrix-cracks and delaminations. An explicit finite element analysis using bilinear cohesive law-based interface elements and cohesive contacts is employed for the investigation. Examples are presented to illustrate the effectiveness of the current models for predicting the extent of impact damage and subsequent compression strength. The current study has improved the understanding of interactions between matrix-cracks and delaminations to clarify open questions on delamination initiation and how matrix cracks and fibre orientations interact. (c) 2012 Elsevier Ltd. All rights reserved.</p

Properties of two composite materials made of toughened epoxy resin and high-strain graphite fiber

Results are presented from an experimental evaluation of IM7/8551-7 and IM6/18081, two new toughened epoxy resin, high strain graphite fiber composite materials. Data include ply-level strengths and moduli, notched tension and compression strengths and compression-after-impact assessments. The measured properties are compared with those of other graphite-epoxy materials

Analysing Compression Techniques for In-Memory Collaborative Filtering

Following the recent trend of in-memory data processing, it is a usual practice to maintain collaborative filtering data in the main memory when generating recommendations in academic and industrial recommender systems. In this paper, we study the impact of integer compression techniques for in-memory collaborative filtering data in terms of space and time efficiency. Our results provide relevant observations about when and how to compress collaborative filtering data. First, we observe that, depending on the memory constraints, compression techniques may speed up or slow down the performance of state-of-the art collaborative filtering algorithms. Second, after comparing different compression techniques, we find the Frame of Reference (FOR) technique to be the best option in terms of space and time efficiency under different memory constraints

Compression shorts reduce prenatal pelvic and low back pain: a prospective quasi-experimental controlled study

Background Common prenatal ailments negatively impact performance of activities of daily living and it has been proposed that the use of dynamic elastomeric fabric orthoses, more commonly referred to as compression garments, during pregnancy might aid in the reduction of pain from these ailments, allowing for improved functional capacity. However, the effectiveness of such garments in this context has not been established. This study aims to determine whether compression shorts are effective and thermally safe in the prevention and management of prenatal pelvic and low back pain (LBP). Method A prospective quasi-experimental controlled study using parallel groups without random allocation was conducted, involving 55 childbearing women (gestational weeks 16–31) recruited from hospital and community-based maternity care providers. The compression shorts group (SG) wore SRC Pregnancy Shorts in addition to receiving usual care. The comparison group (CG) received usual care alone. Primary outcome measures—Numeric Pain Rating Scale (NPRS) and Roland Morris Disability Questionnaire (RMDQ) and secondary measures Pelvic Floor Impact Questionnaire - 7 (PFIQ-7) and SF-36 Short Form Health Survey—were assessed fortnightly over 6-weeks for both groups. The compression SG self-assessed daily their body temperatures to monitor thermal impact. Data analysis involved descriptive analyses of the primary and secondary outcome measures scores by group and time-point, and multivariable linear regressions to assess between-group differences in change scores at 6-weeks from baseline while controlling for baseline factors. Results After controlling for baseline scores, gestational weeks and parity, statistically significant differences in NPRS and RMDQ change scores between groups were in favour of the compression SG. At 6-weeks, mean (SD) NPRS change scores in the compression SG and CG were significantly different, at −0.38 (2.21) and 2.82 (2.68), respectively, p = 0.003. Mean (SD) RMDQ change scores in the compression SG and CG were also significantly different, at 0.46 (3.05) and 3.64 (3.32), respectively, p = 0.009. A total of 883 (99.7%) of the reported daily self-assessed body temperatures ranged between 35.4 and 38.0 °C when wearing the compression shorts. At 6-weeks, mean (SD) PFIQ-7 and SF-36 change scores in the compression SG and CG were not significantly different. Conclusion Compression shorts are effective and thermally safe for prenatal management of pelvic and LBP. Registration Trial registration was not required (Australian Government Department of Health Therapeutic Goods Administration (TGA), 2018)

Durability and damage tolerance of Large Composite Primary Aircraft Structure (LCPAS)

Analysis and testing addressing the key technology areas of durability and damage tolerance were completed for wing surface panels. The wing of a fuel-efficient, 200-passenger commercial transport airplane for 1990 delivery was sized using graphite-epoxy materials. Coupons of various layups used in the wing sizing were tested in tension, compression, and spectrum fatigue with typical fastener penetrations. The compression strength after barely visible impact damage was determined from coupon and structural element tests. One current material system and one toughened system were evaluated by coupon testing. The results of the coupon and element tests were used to design three distinctly different compression panels meeting the strength, stiffness, and damage-tolerance requirements of the upper wing panels. These three concepts were tested with various amounts of damage ranging from barely visible impact to through-penetration. The results of this program provide the key technology data required to assess the durability and damage-tolerance capability or advanced composites for use in commercial aircraft wing panel structure

On the compact wave dynamics of tensegrity beams in multiple dimensions

This work presents a numerical investigation on the nonlinear wave dynamics of tensegrity beams in 1D, 2D and 3D arrangements. The simulation of impact loading on a chain of tensegrity prisms and lumped masses allows us to apply on a smaller scale recent results on the propagation of compression solitary waves in 1D tensegrity metamaterials. Novel results on the wave dynamics of 2D and 3D beams reveal - for the first time - the presence of compact compression waves in two- and three-dimensional tensegrity lattices with slender aspect ratio. The dynamics of such systems is characterized by the thermalization of the lattice nearby the impacted regions of the boundary. The portion of the absorbed energy moving along the longitudinal direction is transported by compression waves with compact support. Such waves emerge with nearly constant speed, and slight modifications of their spatial shape and amplitude, after collisions with compression waves traveling in opposite direction. The analyzed behaviors suggest the use of multidimensional tensegrity lattices for the design and additive manufacturing of novel sound focusing devices

A low cost method of testing compression-after-impact strength of composite laminates

A method was devised to test the compression strength of composite laminate specimens that are much thinner and wider than other tests require. The specimen can be up to 7.62 cm (3 in) wide and as thin as 1.02 mm (.04 in). The best features of the Illinois Institute of Technology Research Institute (IITRI) fixture are combined with an antibuckling jig developed and used at the University of Dayton Research Institute to obtain a method of compression testing thin, wide test coupons on any 20 kip (or larger) loading frame. Up to 83 pct. less composite material is needed for the test coupons compared to the most commonly used compression-after-impact (CAI) tests, which calls for 48 ply thick (approx. 6.12 mm) test coupons. Another advantage of the new method is that composite coupons of the exact lay-up and thickness of production parts can be tested for CAI strength, thus yielding more meaningful results. This new method was used to compression test 8 and 16 ply laminates of T300/934 carbon/epoxy. These results were compared to those obtained using ASTM standard D 3410-87 (Celanese compression test). CAI testing was performed on IM6/3501-6, IM7/SP500 and IM7/F3900. The new test method and associated fixture work well and is a valuable asset to MSFC's damage tolerance program