# Role of Piezoelectric Elements in Finding the Mechanical Properties of Solid Industrial Materials
## Using Piezoelectricity to Calculate Solid-Material Properties
### Creep  
Creep represents plastic deformation in material over time, when this material is subjected to constant stress. This stress is often less than the yield point of the material. Usually, creep does not necessarily mean failure, but it is usually not good. Acute creep tends to increase with increasing temperature.  
To calculate the static creep rate of ice and a frozen soil specimen (394 mm long and 76 mm in diameter subject to \(-3\)\({}^{\circ}\)C), two pieces of PE with frequency ranging from 0 Hz to 1000 Hz were used [2]. In this test, the input motion and output sample resonance are both observed and measured with piezoelectric transducer attached to the cap and base plates at passive and active ends of the specimen.  
Vibrocreep in polymers means an acceleration of creep through the specimen to the cyclic loading regime. This test was used as one of many stages in an experimental program to test the creep in polymers and thin-film of piezoelectric polymer made from polyvinylidene fluoride (PVDF) [3; 4]. The PVDF used can sense very small vibrations from 1 Hz to 20 Hz, slight changes in stress, after more than 10 years and 100 million pressure cycles at a pressure range from 10 kPa to 2 MPa, with approximately 10% accuracy, and about 1 ms response time [3]. In addition, the PVDF can be used in a wide temperature range (\(-40\)\({}^{\circ}\)C to \(+160\)\({}^{\circ}\)C). In another report, PVDF of 4 mm diameter with hosing diameter range of 8 mm to 20 mm was used, which can sense loads with frequency ranging from 0.001 GHz to 2 GHz [4]. These potential properties and their flexibility in use are very difficult to find in many available sensors or smart materials. Thus, most ultrasonic creep tests have utilized PVDF recently [5; 6; 7].  
The Udimet 520 and IN738 LC Ni nickel-based alloy is one of the important alloys in manufacturing gas turbine blades because this material has a high resistance to creep. A previous study reported the relationship between creep life and its effects on ultrasonic waves for these alloys using PE (2.25 MHz, 6 mm diameter that was manually joined to the specimen using a compliant gel) as a dual element transducer (pulse emitter and receiver from the same location) [8]. The overall length of these specimens was 15 cm and the width ranged from 2.25 cm to 3.0 cm.  
To measure the creep in SUS 316L austenitic stainless steel, a control system consisting of PE with a natural frequency of 15 MHz as the valve opening to control the force which comes from the vacuum drum was designed [9]. This application reveals the ability of PE as a high-velocity actuator with small size, which can be used in special applications.  
In the same manner, another report indicated that ultrasonic attenuation increases on two conditions, namely, an increase in the equivalent size of cubical shape \(\gamma^{\prime}\) precipitates and an increase in creep time [10]. This attenuation in ultrasonic waves can be used as a potential non-destructive parameter for evaluating the creep degree for the alloy IN738 LC Ni, as shown in Figure 1. Thus, piezoelectric transducer (PT) with a center frequency of 15 MHz in a pulse echo technique was used to calculate the attenuation in this wave. Then, the degree of creep in this alloy was calculated. In addition, PE was used as a sensor to measure creep in paper peeling [11].