Abstract:The effect of matrix cracking on the delamination morphology inside carbon fiber reinforced plastics (CFRP) laminates during low-velocity impact (LVI) is an open question. In this paper, the relationship between matrix cracking and delamination is studied by using cross-ply laminates. Several methods, including micrograph, C-scan, and visual inspection, were adopted to characterize the damage after LVI experiments. Based on the experimental results, finite element (FE) models were established to analyze the damage mechanisms. The matrix cracking was predicted by the extended finite element method (XFEM) and the Puck criteria, while the delamination was modeled by cohesive elements. It was revealed that the matrix crack in the bottom ply not only promoted the outward propagation of delamination but also contributed to the narrow delamination beneath the impact location. Multiple matrix cracks occurred in the middle ply. The ones close to the plate center initiated the delamination and prevented large-scale delamination beneath the impact location. For the cracks that were far away, no significant effect on delamination was found. In conclusion, the stress redistribution caused by the crack opening determines the delamination.Keywords: low-velocity impact; matrix cracking; delamination; extended finite element method; cohesive element
Haring's family attended the United Church of Christ.[9] In his early teenage years, he was involved with the Jesus Movement.[10] He later hitchhiked across the country, selling T-shirts he made featuring the Grateful Dead and anti-Nixon designs.[11] He graduated from Kutztown Area High School in 1976.[12] He studied commercial art from 1976 to 1978 at Pittsburgh's Ivy School of Professional Art, but eventually lost interest,[13] inspired to focus on his own art after reading The Art Spirit (1923) by Robert Henri.[8]
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The Pop Shop was far from Haring's only effort to make his work widely accessible. Throughout his career, Haring made art in subways and on billboards.[64] His attempts to make his work relatable can also be seen in his figures' lack of discernable ages, races, or identities.[10] By the arrival of Pop Shop, his work began reflecting more socio-political themes, such as anti-Apartheid, AIDS awareness, and the crack cocaine epidemic.[5]
On a hot summer afternoon in August 1998, 37-year-old U.S. Army Sergeant First Class Rossano V. Gerald and his young son Gregory drove across the Oklahoma border into a nightmare. A career soldier and a highly decorated veteran of Desert Storm and Operation United Shield in Somalia, SFC Gerald, a black man of Panamanian descent, found that he could not travel more than 30 minutes through the state without being stopped twice: first by the Roland City Police Department, and then by the Oklahoma Highway Patrol.
The emergence of crack in the spring of 1986 and a flood of lurid and often exaggerated press accounts of inner-city crack use ushered in a period of intense public concern about illegal drugs, and helped reinforce the impression that drug use was primarily a minority problem. Enforcement of the nation's drug laws at the street level focused more and more on poor communities of color. In the mid- to late-1980s, many cities initiated major law enforcement programs to deal with street-level drug dealing. "Operation Pressure Point" in New York was an attempt to rid the predominantly Hispanic Lower East Side of the drug trade. Operation Invincible in Memphis, Operation Clean Sweep in Chicago, Operation Hammer in Los Angeles, and the Red Dog Squad in Atlanta all targeted poor, minority, urban neighborhoods where drug dealing tended to be open and easy to detect.
In the 1980s, with the emergence of the crack market, skin color alone became a major profile component, and, to an increasing extent, black travelers in the nation's airports and found themselves the subjects of frequent interrogations and suspicionless searches by the DEA and the U.S. Customs Service. These law enforcement practices soon spread to train stations and bus terminals, as well.
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