Tensile Creep and Creep Rupture of Continuous Strand Mat Polypropylene Composites

Abstract

ABSIXACT: This paper describes an experimental study on the tensile creep behavior of a random continuous fiber mat reinforced polypropylene composite, commercially known as Azdel. A special experimental setup was designed and used to conduct these creep tests at 75 and 100°C with stress levels ranging from 30 to 60 percent of the tensile strength of Azdel. The test duration was 3,000 hours or the time to creep rupture response, whichever occurred first. A straight line on a semi-log plot adequately described the relationship between the imposed stress and the creep rupture response time for the range of stress levels studied. Moreover, the estimated secondary creep mte was inversely related to the observed creep rupture response time. INTRODUCI'IONELEcriNG COMPOSITE MATERIALS for long term applications at elevated S temperatures requires knowledge of their creep behavior. In creep tests, a constant stress is applied on the specimen and the strain is measured as a function of time. The increase in strain with time is known as creep. Depending on the stress level and ambient temperature, the specimen can also fail, thereby terminating the creep test. This fidure phenomenon is known as creep rupture and occurs at stresses much lower than the static tensile strength of the material.Creep behavior of composite materials has been studied only to a limited extent, mainly due to the fact that continuous fiber composites in thermosetting matrices do not exhibit large creep strains at their use temperature 111. However, creep deformation may be relatively large if the fiber orientation is random and/or the matrix is a thermoplastic resin. There are a few reported studies on the creep characteristics of random fiber sheet molding compound (SMC-R) composites [2-3]. In these studies, the matrix was a thermosetting resin, such as Journal of COMPOSITE MATERIALS,

Time-dependent failure criteria for lifetime prediction of polymer matrix composite structures

“…Also a strong correlation was found between the time of the minimum of the strain rate in the secondary creep regime and the failure time. A related relationship as found by Little [27] for random continuous fibre mat reinforced polypropylene composite. It was found that the estimated secondary creep rate was inversely related to the observed creep rupture response time [27].…”

“…A related relationship as found by Little [27] for random continuous fibre mat reinforced polypropylene composite. It was found that the estimated secondary creep rate was inversely related to the observed creep rupture response time [27]. It is to be noted that this is quite similar to the relationship found out for metals by Monkman and Grant [28].…”

“…Figures (26)(27)(28)(29). Again these results show that the simple linear relationship between the creep stress and the function χ is sufficient to obtain good results.…”

Creep failure of polypropylene: experiments and constitutive modeling

“…8,9 below). According to the concept of diffusive viscosity (Greenwood 1976(Greenwood , 1990 the product˙ min t f remains practically independent of applied stress σ [experimental verification of this statement on a polypropylene composite was given in Little et al (1995)]. Expressing t f from the equalitẏ min t f = C, where C is a constant, and inserting the result into Eq.…”

Creep behaviour of adhesive lap joints in thermoplastics composites

“…The results show three stages typical of creep behaviour; however, the first stage cannot be distinguished due to the logarithmic scale used on the time axis. The primary creep stage is characterized by a decreasing strain rate with time and is usually observed in metals [8], polymeric materials [9], and composite materials [10,11]. The second creep stage presents an approximately constant strain rate, while the third stage has a significant increase in the deformation up to rupture [8][9][10][11].…”