Transverse impact strength

Misch metal or rare earth silicon alloy for controlling shapes of sulfide inclusions and thereby improving transverse impact strength... 

The transverse impact strength is low as there are few, if any, fibres in this direction to contribute to strength and hence impact resistance. The importance of fabrication is shown by the results for PES(l) and PES(2) — melt impregnation presumably gives a better composite. The impact results for PEI are very low for a thermoplastic and again probably indicate the effects of fabrication. 

Eor an impact strength of 34 J (25 ft-lbf) the equivalent fracture toughness (150) is approximately 120 MPay. The fracture toughness dictates the critical size of crack above which fast fracture intervenes, so the smaller its value the smaller the critical crack and hence the greater significance of the transverse impact requirement specified by Manning. 

Tables 4—6 Ust ASTM methods used for the characterization of PB and PMP. A number of specialized methods were developed for testing particular articles manufactured from polyolefins several of these determine the performance of PB and PMP film, including the measurement of the film s dart impact strength and tear strength. Dart impact strength is measured by dropping a heavy dart with a round tip on a stretched film. Tear resistance, which reflects the film s resistance to tear propagation, is measured with the Ehnendorf tear tester. Two values for the tear strength are usually reported, one in the machine dkection of the film and the other in the transverse dkection. Pipes manufactured from PB are tested by pressurizing them internally with water the time-to-burst failure is determined at various temperatures (46). The standard test method for haze and luminous transmittance (ASTM D1003) is used for the measurement of PMP optical characteristics.

To improve the end use performance and make the processability easy, control of MW and MWD as well as the use of.more than one comonomer has been reported for LLDPE [28]. Union Carbide s high MW-LLDPE with broad MWD is a 1-hexene-based resin, and its film provides superior (about 30-50% higher) tensile strength, puncture resistance, and dart impact strength than conventional 1-hexene-based resin, but with lower tear resistance in the transverse direction. The broad MWD makes the resin processability easy on the conventional extruder. 

Use of 4-methylpentene-l comonomer with ethylene provides LLDPE resin have film properties (i.e., tensile strength, modulus, transverse direction tear strength, and impact strength) superior to 1-butene-based LLDPE resin as has been claimed by B.P. Chemicals. 1-Butene has also been used as the second comonomer with 4-methylpentene-l to tailor the properties of LLDPE resin [28], The properties of 4-methylpentene-l-based LLDPE film are given in Table 4. 

Methods employed to determine the impact resistance of plastics include pendulum methods (Izod, Charpy, tensile impact, falling dart, Gardner, Dynatup, etc.) and instrumented techniques. In the case of the Izod test, what is measured is the energy required to break a test specimen transversely struck (the test can be done either with the specimen notched or unnotched). The tensile impact test has a bar loaded in tension and the striking force tends to elongate the bar (Chapter 5, Impact Strength). 

X-65. Reference 22 reported postweld mechanical properties in 6 mm (0.25 in.) thick FSW X-65 pipe. Transverse tensile strengths were equivalent to the base metal. All tensile samples fractured in the base metal well removed from the weld or HAZ. Charpy impact results in the weld nugget and HAZ exceeded that of the base metal at -50, 0, and 20 °C (-58, 32, and 68 °F). These results are shown in Fig. 6.2. 

The range over which the state of orientation can be changed in the film blowing operation and the resulting effects on mechanical properties have been demonstrated by Bates.He investigated the effect of both transverse and longitudinal orientation on the impact strength of low density polyethylene. 

Fig, 7. Impact strength of low density polyethylene fihns with a varying ratio of machine-direction (fj) versus transverse-direction orientation (V2) as determined by reversion measurements, (The numbers on the graph denote fi,)... 

The values of the elongation at fracture and of the impact strength depend on the direction of sampling (longitudinal = higher values transversal = lower values) and on the thickness of the sheet or rod (increase of thickness = decrease of value). 

Notched impact strength (Charpy) (kJ/m ) Sound velocity Vs (m/s) (longitudinal) Sound velocity Us (m/s) (transverse)... 

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