KNOCK DETECTION BY AUDIBLE, ACCELEROMETER, PRESSURE AND IONIC CURRENT METHODS.

This paper describes the ways which are used at the present time by the Ford Motor Company for the detection of knock. A description of the available methods is given, and their relative effectiveness is assessed by analysing data taken simultaneously by all of these methods. It is shown that no one technique has an overwhelming advantage, but that each technique has its individual merits and demerits.

Do we know the strength of the chorioamnion? A critical review and analysis

The chorioamnion is the membrane that surrounds the fetus during gestation. Normally, it must remain intact for the duration of pregnancy, 37-42 weeks, and only rupture during or just before labour and delivery of the fetus. In a significant number (3%) of all births, this does not happen, and membranes rupture before term, resulting in preterm birth and significant perinatal morbidity. It is known that the material properties of chorioamnion may play a major role in mechanical rupture; a number of studies have been undertaken to characterise the physical nature of chorioamnion and examine factors that may predispose to rupture. However, the existing literature is inconsistent in its choice of both physical testing methods and data analysis techniques, motivating the current review. Experimental data from a large number of chorioamnion mechanical studies were collated, and data were converted to standard engineering quantities. The failure strength of the chorioamnion membrane was found consistently to value approximately 0.9 MPa. It is hoped that past and future studies of membrane mechanics can provide insight into the role of chorioamnion in labour and delivery. In addition, biomechanical approaches can help elucidate the potential causes of early rupture, and suggest future protocols or treatments that could both diagnose and prevent its occurrence. © 2009 Elsevier Ireland Ltd.

Strength mobilization in clays and silts

A large database of 115 triaxial, direct simple shear, and cyclic tests on 19 clays and silts is presented and analysed to develop an empirical framework for the prediction of the mobilization of the undrained shear strength, cu, of natural clays tested from an initially isotropic state of stress. The strain at half the peak undrained strength (γM=2) is used to normalize the shear strain data between mobilized strengths of 0.2cu and 0.8cu. A power law with an exponent of 0.6 is found to describe all the normalized data within a strain factor of 1.75 when a representative sample provides a value for γM=2. Multi-linear regression analysis shows that γM=2 is a function of cu, plasticity index Ip, and initial mean effective stress p′0. Of the 97 stress-strain curves for which cu, Ip, and p′0 were available, the observed values of γM=2 fell within a factor of three of the regression; this additional uncertainty should be acknowledged if a designer wished to limit immediate foundation settlements on the basis of an undrained strength profile and the plasticity index of the clay. The influence of stress history is also discussed. The application of these stress-strain relations to serviceability design calculations is portrayed through a worked example. The implications for geotechnical decision-making and codes of practice are considered.