Puncture loading

Resistance to puncture is another type of loading. It is of particular interest in applications involving sheet and film as well as thin-walled tubing or molding and other membrane type loaded structures. Hie surface skins of sandwich panels are another area where it is important. A localized force is applied by a relatively sharp object perpendicular to the plane of the sheet of material being stressed. If the material is thick compared to the area of application of the stress, it is effectively a localized compression stress with some shear effects as the material is deformed below the surface of the sheet. 

In the case of a thin sheet or film the stresses cause the material to be displaced completely away from the plane of the sheet and the restraint is by tensile stress in the sheet and by hoop stress around the puncturing member. Most cases fall somewhere between these extremes, but the most important conditions in practice involve the second condition to a larger degree than the first condition. 

To analyze the second condition take the material at the point where the puncturing object has almost pierced the membrane but has not broken through. At this point one can see the nature of the forces which are 

Based on this analysis it is evident that materials which are biaxially oriented will have good puncture resistance. Highly polar polymers would be resistant to puncture failure because of their tendency to increase in strength when stretched. The addition of randomly dispersed fibrous filler will also add resistance to puncture loads. From some examples such as oriented polyethylene glycol terephthalate (Mylar), vulcanized fiber, and oriented nylon, it is evident that these materials meet one or more of the conditions reviewed. Products and plastics that meet with puncture loading conditions in applications can be reinforced against this type of stress by use of a surface layer of plastic with good puncture resistance. Resistance of the surface layer to puncture will protect the product from puncture loads. An example of this type of application is the addition of an oriented PS layer to foam cups to improve their performance. 

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Fig. 4.60 Schematic representation of load (F) - deflection (/) diagrams resulting from different material behaviour with Fin - maximum load, /m - deflection at maximum load, - energy up to maximum load, Fp - puncture load corresponding to Fm/2, /p - deformation at puncture load and Fr - crack propagation energy.

Fig. 7-3. Deflections by point puncture loading of thick and thin sheets. Reference Modern Plastics May 1964 article on repeated tensile impact.

Fig. 7-4. Stresses induced in thin material by puncture loading.

Puncture loading is very applicable in applications with sheet and film as well as thin-walled tubing or molding, surface skins of sandwich... 

Plastics that are biaxially oriented have good puncture resistance. Highly polar polymers would be resistant to puncture failure because of their tendency to increase in strength when stretched. The addition of randomly dispersed fibrous filler will also add resistance to puncture loads. 

Anisotropic materials will have a more complicated force pattern. Uniaxially oriented materials will split rather than pimcture imder puncturing loading. To improve the puncture resistance materials are needed with high tensile strength. In addition, the material should have a high compression modulus to resist the point penetration into the material. Resistance to notch loading is also important. 

I Puncture load sufficient to fail tank head J Puncture strikes tank head... 

There are a number of basic forms of energy loads or impingement on products to which plastics react in a manner different from other materials. These dynamic stresses include loading due to impact, impulse, puncture, frictional, hydrostatic, and erosion. They have a difference in response and degree of response to other forms of stress. Analyzing these differences provides... 

ASTM D3763, Test Methodfor High-Speed Puncture Properties ofPlastics Using Load and Displacement Sensors, Vol. 8.02, ASTM, Philadelphia, Pa., 1993. 

The principal differences between the 1992 and 1999 trial bums were the rates of agent loading and the types of containers processed. In 1992, agent was introduced to the MPF in a single ton container that had been punctured in 1999, agent was introduced in a tray of 96 projectiles filled to... 

For premedication aspirin 300 mg twice a day 48 hours prior to the procedure and a loading dose of clopidogrel 300 mg (or ticlopidine 250 mg) is recommended. Endocarditis prophylaxis with a first generation cephalosporin (e.g., cefuroxime, 1, 5 g, i.v.) should be administered before and after intervention. After transseptal puncture, 10,000 units of heparin are administered. An activated clotting time of 200-300 seconds is desirable. 

Other common chemicals could be deliberately released into the environment, putting wider populations at risk. This could occur within a facility or perhaps by sabotaging a container en route via train or road. During the Atlanta 1996 Olympics, for example, U.S. federal authorities considered potential threats from improvised chemical devices, including the use of high explosives to puncture a train car loaded with toxic chemicals (U.S. Army Medical Command, 1999). 

The protein concentration in the glomerular filtrate has been measured in a number of animal models by direct glomerular puncture. The concentration of total protein found is in the range of several hundredmg/L (approximately 1% of plasma), with albumin concentrations ranging from a few hundred to less than 40 mg/L. The filtered load of protein depends on the product of the GSC and the free... 

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